• Aucun résultat trouvé

IHP-III man's

N/A
N/A
Protected

Academic year: 2022

Partager "IHP-III man's"

Copied!
73
0
0

Texte intégral

(1)
(2)

Methodology for distinguishing between man's influence and climatic effects

on the hydrological cycle

J.C. Refsgaard,

W.M. Alley and

V.S.

Vuglinsky

IHP-III Project 6.3

Unesco, Pans, 1989

s c -

8

9/."3-

2 2

(3)

of any country, territory, city or o f its authorities, or concerning t h e delimitation of its frontiers or boundaries.

(4)

PREFACE

A l t h o u g h t h e t o t a l amount o f w a t e r on E a r t h i s g e n e r a l l y assumed t o h a v e r e - mained v i r t u a l l y c o n s t a n t during r e c o r d e d h i s t o r y , p e r i o d s o f f l o o d and d r o u g h t have c h a l l e n g e d t h e i n t e l l e c t o f man t o have t h e c a p a c i t y t o c o n t r o l t h e w a t e r r e s o u r c e s a v a i l a b l e t o h i m . C u r r e n t l y , t h e r a p i d g r o w t h o f popu- l a t i o n , t o g e t h e r w i t h t h e e x t e n s i o n o f i r r i g a t e d a g r i c u l t u r e and i n d u s t r i a l development, a r e s t r e s s i n g t h e q u a n t i t y and q u a l i t y a s p e c t s o f t h e n a t u r a l system. Because o f t h e i n c r e a s i n g problems, man has begun t o r e a l i z e t h a t he can no l o n g e r f o l l o w a "use and d i s c a r d " p h i l o s o p h y

--

e i t h e r w i t h w a t e r r e - s o u r c e s o r any o t h e r n a t u r a l r e s o u r c e . As a r e s u l t , t h e need f o r a c o n s i s t e n t p o l i c y o f r a t i o n a l management o f w a t e r r e s o u r c e s h a s become e v i d e n t .

R a t i o n a l w a t e r management, however, s h o u l d b e founded upon a t h o r o u g h u n d e r s t a n d i n g o f w a t e r a v a i l a b i l i t y and movement. Thus, as a c o n t r i b u t i o n t o t h e s o l u t i o n o f t h e w o r l d ' s w a t e r p r o b l e m s , Unesco, i n 1985, began t h e f i r s t w o r l d w i d e programme o f s t u d i e s o f t h e h y d r o l o g i c a l c y c l e

--

t h e I n t e r n a t i o n a l H y d r o l o g i c a l Decade ( I H D ) . The r e s e a r c h programme was complemented by a m a j o r e f f o r t i n t h e f i e l d o f h y d r o l o g i c a l e d u c a t i o n and t r a i n i n g . The a c t i v i t i e s u n d e r t a k e n during t h e Decade p r o v e d t o b e o f g r e a t i n t e r e s t and v a l u e t o Member S t a t e s . B y t h e end o f t h a t p e r i o d , a m a j o r i t y o f U n e s c o ' s Member S t a t e s h a d formed I H D N a t i o n a l Committees t o c a r r y o u t t h e r e l e v a n t n a t i o n a l a c t i v i - t i e s and t o p a r t i c i p a t e i n r e g i o n a l and i n t e r n a t i o n a l c o - o p e r a t i o n w i t h i n t h e I H D programme. The knowledge o f t h e w o r l d ' s w a t e r r e s o u r c e s as a n i n d e p e n d e n t p r o f e s s i o n a l o p t i o n and f a c i l i t i e s f o r t h e t r a i n i n g o f h y d r o l o g i s t s h a d b e e n developed.

Conscious o f t h e need t o expand upon t h e e f f o r t s i n i t i a t e d d u r i n g t h e I n t e r n a t i o n a l H y d r o l o g i c a l Decade, and, f o l l o w i n g t h e recommendations o f Member S t a t e s , Unesco, i n 1975, l a u n c h e d a new l o n g - t e r m i n t e r g o v e r n m e n t a l programme

,

t h e I n t e r n a t i o n a l H y d r o l o g i c a l Programme (IHP)

,

t o f o l l o w t h e De- cade.

A l t h o u g h t h e I H P i s b a s i c a l l y a s c i e n t i f i c and e d u c a t i o n a l programme, Unesco has been aware f r o m t h e b e g i n n i n g o f a need t o d i r e c t i t s a c t i v i t i e s t o w a r d s t h e p r a c t i c a l s o l u t i o n s o f t h e w o r l d ' s v e r y r e a l w a t e r r e s o u r c e s p r o b - lems. A c c o r d i n g l y , and i n l i n e w i t h t h e recommendations o f t h e 1977 U n i t e d N a t i o n s Water Conference, t h e o b j e c t i v e s o f t h e I n t e r n a t i o n a l H y d r o l o g i c a l Programme have been g r a d u a l l y expanded i n o r d e r t o c o v e r n o t o n l y h y d r o l o g i c a l p r o c e s s e s c o n s i d e r e d i n i n t e r r e l a t i o n s h i p w i t h t h e environment and human ac- t i v i t i e s , but a l s o t h e s c i e n t i f i c a s p e c t s o f m u l t i - p u r p o s e u t i l i z a t i o n and c o n s e r v a t i o n of w a t e r r e s o u r c e s t o meet t h e needs o f economic and s o c i a l de- velopment. Thus, w h i l e m a i n t a i n i n g I H P ' s s c i e n t i f i c c o n c e p t , t h e o b j e c t i v e s have s h i f t e d p e r c e p t i b l y t o w a r d s a m u l t i d i s c i p l i n a r y approach t o t h e assess- m e n t , p l a n n i n g and r a t i o n a l management o f w a t e r r e s o u r c e s .

As p a r t o f IJnesco's c o n t r i b u t i o n t o t h e o b j e c t i v e s o f t h e I H P , t w o pub- l i c a t i o n s e r i e s a r e i s s u e d : " S t u d i e s and R e p o r t s i n H y d r o l o g y " and " T e c h n i c a l Papers i n H y d r o l o g y " . I n a d d i t i o n t o t h e s e p u b l i c a t i o n s , and i n o r d e r t o ex- p e d i t e exchange o f i n f o r m a t i o n , some works a r e i s s u e d i n t h e f o r m o f T e c h n i c a l Documents.

(5)

The h y d r o l o g i c a l c y c l e i s i n f l u e n c e d b o t h b y t h e c l i m a t e and by catchment c h a r a c t e r i s t i c s such as t o p o g r a p h y , g e o l o g y , s o i l , v e g e t a t i o n , and w a t e r development. A methodology i s p r e s e n t e d f o r d i s t i n g u i s h i n g between t h e e f f e c t s o f man's a c t i v i t y and c l i m a t e on t h e h y d r o l o g i c a l c y c l e , i n p a r t i c u l a r stream- f l o w and g r o u n d w a t e r . The methodology i s b a s e d on j o i n t a p p l i c a t i o n o f s t a t i - s t i c a l t r e n d t e s t i n g methods and h y d r o l o g i c a l ( o r s t a t i s t i c a l r e g r e s s i o n ) models o f s t r e a m f l o w o r g r o u n d w a t e r . The methodology i s i l l u s t r a t e d b y two

case s t u d i e s .

(6)

TAIjLE OF CONTENTS

P a g e FOREWORD

1.

2 .

3.

4.

5.

INTRODUCTION 1.1 B a c k g r o u n d

1 . 2 F a c t o r s A f f e c t i n g t h e H y d r o l o g i c a l C y c l e 1 . 3 C o n t e n t s o f t h e R e p o r t

SUMMARY AND RECOMMENDATIONS

2 . 1 M e t h o d o l o g y 2.2 S t a t e o f t h e A r t 2 . 3 R e c o m m e n d a t i o n s HYDROLOGICAL TOOLS 3 . 1 I n t r o d u c t i o n

3 . 2 D e t e r m i n i s t i c M o d e l s 3 . 2 . 1 E m p i r i c a l m o d e l s

3.2.2 Lumped, c o n c e p t u a l m o d e l s

3.2.3 D i s t r i b u t e d , p h y s i c a l l y based m o d e l s 3.2.4 S e l e c t i o n o f a p p r o p r i a t e m o d e l t y p e 3 . 2 . 5 V a l i d a t i o n o f h y d r o l o g i c a l m o d e l s 3 . 3 S t a t i s t i c a l M o d e l s

S T A T I S T I C A L METHODS 4 . 1 I n t r o d u c t i o n 4.2 S t e p T r e n d s 4 . 3 M o n o t o n i c T r e n d s 4.4 C o m p l i c a t i o n s

METHODOLOGY FOR D I S T I N G U I S H I N G BETWEEN MAN'S INFLUENCE AND CLIMATE V A R I A B I L I T Y

5 . 1 I n t r o d u c t i o n

5.2 STEP 1: D e t e r m i n a t i o n o f S t e p o r M o n o t o n i c 5 . 3 STEP 2 : S e l e c t i o n o f M o d e l T y p e

5 . 4 STEP 3: M o d e l C a l i b r a t i o n , V a l i d a t i o n and A p p l i c a t i o n

5 . 4 . 1 Lumped, c o n c e p t u a l m o d e l s

5.4.2 D i s t r i b u t e d , p h y s i c a l l y b a s e d m o d e l s 5.4.3 S t a t i s t i c a l r e g r e s s i o n m o d e l s

5 . 5 STEP 4: T r e n d T e s t 5 . 5 . 1 No m o d e l

5.5.2 Lumped, c o n c e p t u a l m o d e l s

5 . 5 . 3 D i s t r i b u t e d , p h y s i c a l l y based m o d e l s 5.5.4 S t a t i s t i c a l r e g r e s s i o n m o d e l s

5.6.1 N o m o d e l

5.6.2 Lumped, c o n c e p t u a l m o d e l

5.6.3 D i s t r i b u t e d , p h y s i c a l l y b a s e d m o d e l 5.6.4 S t a t i s t i c a l r e g r e s s i o n m o d e l s

T r e n d A n a l y s i s

5.6 STEP 5: F u r t h e r H y d r o l o g i c a l A n a l y s i s

1-1 1-1 1 - 2 1 - 4 2 - 1 2 - 1 2-3 2-3 3 - 1 3 - 1 3 - 1 3-2 3-3 3-4 3-5 3-7 3 - 8 4 - 1 4 - 1 4-3 4-3 4-5 5 - 1 5 - 1 5 - 1 5-3 5 - 4 5-4 5 - 5 5 - 8 5-8 5-8 5-8 5-9 5 - 9 5 - 1 1 5 - 1 1 5 - 1 1 5 - 1 1 5-12

(7)

7. CASE STUDIES 7 . 1 I n t r o d u c t i o n

7.2 Groundwater Development i n t h e Kqge

A

and Suss Catchments, Denmark

7 . 2 . 1 D e s c r i p t i o n o f catchments and 7.2.2 Example 1 : Kqge

A

7.2.3 Example 2 : Sus; a t V e t t e r s l e v 7.2.4 R e f e r e n c e s

h y d r o l o g i c a l models

7 . 3 The B l u e R i v e r B a s i n , Nebraska, USA

7 - 1 7- 1 7- 2 7- 2 7-5 7-8 7 - 1 1 7-12

APPENDIX A : I n f l u e n c e o f G l o b a l C l i m a t e Changes on Water Resources.

(M.1. Budyko and K.Y. V i n n i k o v )

(8)

FOREWORD

T h i s r e p o r t o n "Methodology f o r D i s t i n g u i s h i n g between Man's I n f l u e n c e and C l i m a t i c E f f e c t s on t h e H y d r o l o g i c a l C y c l e " emanates f r o m t h e I n t e r n a t i o n a l H y d r o l o g i c a l Programme (IHP) I n t e r g o v e r n m e n t a l C o u n c i l w h i c h , i n 1984, a p p o i n t e d t h e f o l l o w i n g f o u r r a p p o r t e u r s f o r t h e I H P - I 1 1 P r o j e c t 6 . 3

M r . J.C. R e f s g a a r d ( D a n i s h H y d r a u l i c I n s t i t u t e , Denmark)

,

P r i n c i p a l R a p p o r t e u r

M r . W.M. A l l e y (U.S. G e o l o g i c a l Survey, U S A ) , C O - r a p p o r t e u r

M r . D.A. K r a i j e n h o f f ( A g r i c u l t u r a l U n i v e r s i t y Wageningen, N e t h e r l a n d s )

,

C O - r a p p o r t e u r

M r . V.S. V u g l i n s k y ( S t a t e H y d r o l o g i c a l I n s t i t u t e L e n i n g r a d , USSR)

,

C O - r a p p o r t e u r

M r . D.A. K r a i j e n h o f f w i t h d r e w f r o m t h e g r o u p i n August 1988.

The Terms o f Reference drawn b y t h e IHP C o u n c i l f o r t h e p r o j e c t a r e :

o E s t a b l i s h m e n t o f a methodology f o r d i s t i n g u i s h i n g between man's i n f l u e n c e and c l i m a t e v a r i a b i l i t y i n t h e h y d r o l o g i c a l c y c l e , i n p a r t i c u l a r stream- f l o w and groundwater.

o P r e p a r a t i o n o f a s t a t e - o f - t h e - a r t r e p o r t on m e t h o d o l o g i e s f o r d i s - t i n g u i s h i n g between man's i n f l u e n c e and c l i m a t e v a r i a b i l i t y i n t h e h y d r o - l o g i c a l c y c l e .

The p r i n c i p a l r a p p o r t e u r p a r t i c i p a t e d i n t h e t h i r d p l a n n i n g m e e t i n g o n t h e W o r l d C l i m a t e Programme-Water Geneva 1 8 - 2 2 November, 1985, f o r c o o r d i n a - t i o n o f t h i s p r o j e c t w i t h o t h e r r e l a t e d o n g o i n g a c t i v i t i e s . The r a p p o r t e u r s m e t f o r a w o r k i n g s e s s i o n i n P a r i s , 18-22 May, 1987. The f i n a l p r o j e c t co- o r d i n a t i o n was c a r r i e d o u t i n c o n n e c t i o n w i t h t h e f o u r t h p l a n n i n g m e e t i n g on t h e W o r l d C l i m a t e Programme

-

Water, i n P a r i s September 12-16, 1988, where t h r e e o f t h e r a p p o r t e u r s p a r t i c i p a t e d .

The work h a s b e e n s u p p o r t e d by a s s i s t a n c e f r o m t h e D i v i s i o n o f Water Science o f t h e U n i t e d N a t i o n s E d u c a t i o n a l , S c i e n t i f i c and C u l t u r a l O r g a n i z a - t i o n (UNESCO) r e p r e s e n t e d by M r . M . I . R u s i n o v up t o August 1988 and M r . W.H.

G i l b r i c h f o r t h e r e m a i n i n g p e r i o d .

(9)

1. INTRODUCTION 1.1 Backsround

Man's development o f w a t e r r e s o u r c e s h a s r e s u l t e d i n g r e a t economic and s o c i a l b e n e f i t s b y p r o v i d i n g f a v o u r a b l e e n v i r o n m e n t s f o r a g r i c u l t u r e , i n d u s t r y and l i v i n g c o n d i t i o n s . However, i f n o t c a r e f u l l y p l a n n e d , a d v e r s e e f f e c t s may a l s o o c c u r . The assessment o f t h e i n f l u e n c e o f man's management a c t i v i t i e s o n t h e h y d r o l o g i c a l c y c l e and o n t h e W o r l d ' s c l i m a t e i s t h e r e f o r e becoming a p r o b l e m o f i n c r e a s i n g c o n c e r n .

The e f f e c t o f human a c t i v i t y on t h e l a n d and w a t e r r e s o u r c e s o f t h e e a r t h h a s been v i s i b l e s i n c e man s t a r t e d a g r i c u l t u r a l p r o d u c t i o n . However, w i t h t h e r a p i d i n c r e a s e i n p o p u l a t i o n , a g r i c u l t u r a l p r o d u c t i o n and i n d u s t r i a l i z a t i o n man's i n f l u e n c e on t h e h y d r o l o g i c a l c y c l e has i n c r e a s e d g r e a t l y i n r e c e n t de- cades. The p r e d i c t i o n o f t h e h y d r o l o g i c a l e f f e c t s o f man's a c t i v i t y h a s t h e r e - f o r e become i n c r e a s i n g l y i m p o r t a n t .

The e f f e c t o f human a c t i v i t y on t h e g l o b a l c l i m a t e h a s been n e g l i g i b l e o r n o t r e c o g n i z e d u n t i l r e c e n t l y . However, t h e r e i s i n c r e a s i n g c o n c e r n a b o u t man- i n d u c e d g l o b a l c l i m a t e changes i n t h e n e x t f e w decades r e s u l t i n g f r o m i n c r e a s - i n g c o n c e n t r a t i o n s o f c a r b o n d i o x i d e and o t h e r t r a c e gases. One o f t h e most i m p o r t a n t i m p a c t s t o s o c i e t y o f such f u t u r e c l i m a t e changes w i l l be changes i n t h e w a t e r r e s o u r c e s a v a i l a b i l i t y .

I n t h e p r e s e n t r e p o r t t h e t e r m c l i m a t e v a r i a b i l i t y i s d e f i n e d as t h e va- r i a t i o n f r o m y e a r t o y e a r , w h i l e t h e t e r m c l i m a t e change i s d e f i n e d as a s i g - n i f i c a n t change i n c l i m a t e v a r i a b l e s f r o m one p e r i o d t o a n o t h e r p e r i o d . C l i - mate v a r i a b i l i t y i s g e n e r a l l y an e f f e c t o f n a t u r a l c o n d i t i o n s , w h i l e c l i m a t e change can b e caused b o t h by n a t u r a l c o n d i t i o n s and by man's a c t i v i t y .

Long h y d r o l o g i c a l and m e t e o r o l o g i c a l t i m e s e r i e s may b e a n a l y s e d w i t h t h e o b j e c t i v e o f m a k i n g i n f e r e n c e s r e g a r d i n g c l i m a t e v a r i a b i l i t y and i t s e f f e c t on t h e h y d r o l o g i c a l regime. Such r e s e a r c h s t u d i e s a r e p r e s e n t l y b e i n g c a r r i e d o u t w i t h i n t h e framework o f t h e W o r l d C l i m a t e Programme. I n t h i s c o n n e c t i o n , i t i s n e c e s s a r y t o b e a b l e t o i d e n t i f y and t o e l i m i n a t e t h e e f f e c t s o f man's a c t i v i - t y from t h e h y d r o l o g i c a l t i m e s e r i e s .

S i m i l a r l y , l o n g h y d r o l o g i c a l and m e t e o r o l o g i c a l t i m e s e r i e s can b e ana- l y s e d f o r i n v e s t i g a t i n g t h e e f f e c t s o f man's a c t i v i t y . However, o f t e n t h e man- i n d u c e d changes a r e s m a l l compared t o t h e e f f e c t s o f c l i m a t e v a r i a b i l i t y . F u r - t h e r m o r e , t h e changes a r e o f t e n masked b y measurement e r r o r s . D e t e c t i o n o f such changes i s t h e r e f o r e d i f f i c u l t , e s p e c i a l l y f o r s h o r t o b s e r v a t i o n p e r i o d s . Thus i t i s i m p o r t a n t t o e s t a b l i s h a m e t h o d o l o g y f o r d i s t i n g u i s h i n g b e - tween t h e e f f e c t s o f man's i n f l u e n c e and c l i m a t e on t h e h y d r o l o g i c a l c y c l e .

(10)

1 - 2

1 . 2 F a c t o r s A f f e c t i n g t h e H y d r o l o g i c a l C y c l e

T h e i n t e r a c t i o n s between man's a c t i v i t y , t h e c l i m a t e , t h e catchment charac- t e r i s t i c s and t h e h y d r o l o g i c a l c y c l e a r e i l l u s t r a t e d i n F i g . 1 . 2 . 1 .

Man's a c t i v i t i e s a r e i n f l u e n c e d b y t h e c l i m a t i c and t h e catchment c o n d i - t i o n s . T h i s i s o f t e n most o b v i o u s f o r man's a g r i c u l t u r a l a c t i v i t i e s , b u t i s g e n e r a l l y v a l i d .

I n t h e p r e s e n t t e x t t h e t e r m catchment c h a r a c t e r i s t i c s i n a d d i t i o n t o n a t u r a l c h a r a c t e r i s t i c s such as geology, s o i l s , and t o p o g r a p h y a l s o i n c l u d e s man-made s t r u c t u r e s such as w a t e r d i v e r s i o n and groundwater pumpage schemes.

C L I M A T E

o p r e c i p i t a t i o n o r a d i a t i o n o t e m p e r a t u r e o w i n d

o h u m i d i t y

M A N ' S ACTIVITY o f o r e s t r y o a g r i c u l t u r e o u r b a n i z a t i o n o i n d u s t r i a l i z a t i o n

o w a t e r r e s o u r c e s m a n a g e m e n t

C A T C H M E N T C H A R A C T E R L S T I C S

( e i t h e r n a t u r a l o r i n f l u e n c e d b y man) o g e o l o g y , s o i l s , t o p o g r a p h y

o l a k e s a n d swamps o d r a i n a g e s y s t e m o v e g e t a t i o n , l a n d u s e o h y d r a u l i c s t r u c t u r e s

H Y D R O L O G I C A L C Y C L E o p r e c i p i t a t i o n o s o i l m o i s t u r e o e v a p o t r a n s p i r a t i o n o g r o u n d w a t e r

o s t r e a m f l o w

F i g . 1 . 2 . 1 The p r i n c i p a l i n t e r a c t i o n s among man's a c t i v i t y , t h e c l i m a t e , t h e catchment c h a r a c t e r i s t i c s and t h e h y d r o l o g i c a l c y c l e .

(11)

Man's a c t i v i t y can have a c o n s i d e r a b l e i m p a c t on t h e catchment c h a r a c t e - r i s t i c s and hence on t h e h y d r o l o g i c a l r e g i m e . Depending o n t h e n a t u r e o f t h i s i m p a c t , man's a c t i v i t y may b e c l a s s i f i e d i n t o t h e f o l l o w i n g c a t e g o r i e s .

o A c t i v i t i e s l e a d i n g t o changes i n t h e v e g e t a t i o n and l a n d u s e ( d e f o r e s t a - t i o n and a f f o r e s t a t i o n , a g r i c u l t u r e , d r a i n a g e o f swamps and m a r s h - r i d d e n a r e a s , u r b a n i z a t i o n , e t c . )

o A c t i v i t i e s l e a d i n g t o changes i n t h e t o p o g r a p h y and d r a i n a g e system (con- s t r u c t i o n o f v a r i o u s h y d r a u l i c s t r u c t u r e s such as dams, b a r r a g e s , embank- ments

,

p o l d e r s

,

t e r r a c e s

,

and c o n t o u r p l o w i n g )

.

o A c t i v i t i e s l e a d i n g t o d i r e c t and i n d i r e c t w a t e r d i v e r s i o n s f r o m o r t o t h e r i v e r o r t h e groundwater system ( s u r f a c e and g r o u n d w a t e r a b s t r a c t i o n f o r use o u t s i d e t h e a r e a

,

e f f l u e n t d i s c h a r g e

,

a r t i f i c i a l g r o u n d w a t e r r e - c h a r g e , d r a i n a g e , i r r i g a t i o n , e t c . )

The e x t e n t o f man's i n f l u e n c e on t h e catchment c h a r a c t e r i s t i c s c a n v a r y , r a n g i n g from n e a r z e r o i n f l u e n c e i n t h e cases o f n a t u r a l f o r e s t s and o t h e r n o n - c u l t i v a t e d a r e a s w i t h o u t any w a t e r development t o c l o s e t o 1 0 0 % i n f l u e n c e i n t h e case of a p o l d e r a r e a , where t h e t o p o g r a p h y , d r a i n a g e s y s t e m and v e g e t a t i o n a r e man-made and where t h e h y d r o l o g i c a l system i s more o r l e s s com- p l e t e l y r e g u l a t e d .

Man's a c t i v i t i e s c a n have some i n f l u e n c e on t h e l o c a l c l i m a t e ( h u n d r e d s t o thousands of square k i l o m e t r e s ) . F o r example, i t h a s been documented t h a t u r b a n i z a t i o n i n some cases can cause a s i g n i f i c a n t i n c r e a s e i n t h e h i g h i n t e n - s i t y r a i n f a l l . W i t h r e s p e c t t o t h e r e g i o n a l and g l o b a l c l i m a t e , man's a c t i v i - t i e s have i n t h e p a s t a p p a r e n t l y o n l y h a d n e g l i g i b l e e f f e c t s on t h e h y d r o - l o g i c a l c y c l e . The r e s e a r c h r e s u l t s o b t a i n e d b y S o v i e t s c i e n t i s t s show, f o r example, t h a t i n case o f l y g e - s c a l e i r r i g a t i o n p r o j e c t s , c o v e r i n g an a r e a i n t h e o r d e r o f 400-500,000 k m

,

t h e change i n t h e a n n u a l p r e c i p i t a t i o n does n o t exceed 1 - 2 % ( G r i g o r i e v a e t a l . 1 9 8 3 ) .

However, m a n ' s a c t i v i t y may cause a s i g n i f i c a n t change i n t h e g l o b a l c l i - mate i n t h e f u t u r e . Thus, many s c i e n t i s t s s u p p o r t t h e h y p o t h e s i s t h a t t h e i n - c r e a s e o f c a r b o n d i o x i d e c o n c e n t r a t i o n i n t h e atmosphere due t o t h e burning o f f o s s i l f u e l s w i l l cause a g l o b a l t e m p e r a t u r e i n c r e a s e i n t h e coming decades,

(see Appendix A o f t h i s r e p o r t ) . T h i s i n c r e a s e o f t h e mean g l o b a l a i r tempera- t u r e may have s i g n i f i c a n t e f f e c t s on t h e h y d r o l o g i c a l regime i n v a r i o u s r e - g i o n s o f t h e E a r t h .

The h y d r o l o g i c a l c y c l e i s a f f e c t e d by b o t h t h e c l i m a t e and t h e c a t c h m e n t c h a r a c t e r i s t i c s . B o t h catchment c h a r a c t e r i s t i c s and c l i m a t e a r e i n turn a f - f e c t e d b y t h e h y d r o l o g i c a l c y c l e . F o r example, t h e w a t e r a v a i l a b i l i t y i n t h e h y d r o l o g i c a l c y c l e may a f f e c t c a t c h m e n t c h a r a c t e r i s t i c s such as t h e t y p e and t h e e x t e n t o f v e g e t a t i o n . S i m i l a r l y , t h e h y d r o l o g i c a l c y c l e , i n c l u d i n g t h e exchange o f w a t e r and e n e r g y a c r o s s t h e s o i l s u r f a c e t h r o u g h e v a p o r a t i o n , h a s l a r g e e f f e c t s on t h e c l i m a t e .

Man's i n f l u e n c e on t h e c l i m a t e i s b e i n g s t u d i e d u n d e r t h e W o r l d C l i m a t e Programme. The i m p a c t o f c l i m a t e v a r i a b i l i t y on t h e h y d r o l o g i c a l c y c l e i s a l s o b e i n g s t u d i e d u n d e r t h e w o r l d C l i m a t e Programme, e.g. Klemes ( 1 9 8 5 ) . Man's i n f l u e n c e on t h e h y d r o l o g i c a l c y c l e by a f f e c t i n g t h e catchment c h a r a c t e r i s t i c s has b e e n documented by v a r i o u s s c i e n t i s t s , e.g. UNESCO ( 1 9 8 0 ) .

(12)

1 - 4

The c o m p l e x i t y o f t h e s e i n t e r r e l a t i o n s may b e i l l u s t r a t e d b y an example.

I f t h e c l i m a t e , e i t h e r a s a consequence o f a change o r as t h e r e s u l t o f l o n g - t e r m v a r i a b i l i t y , becomes d r y e r ( l e s s p r e c i p i t a t i o n ) € o r a p e r i o d o f some de- cades man may change t h e a g r i c u l t u r a l p r a c t i c e s f r o m i r r i g a t e d f a r m i n g t o d r y l a n d f a r m i n g . T h i s change i n l a n d use w i l l reduce t h e e v a p o t r a n s p i r a t i o n l o s s - es and t h u s t o some e x t e n t compensate f o r t h e r e d u c t i o n i n p r e c i p i t a t i o n . I f s t r e a m f l o w r e c o r d s f r o m two p e r i o d s , b e f o r e and a f t e r t h e c l i m a t e change, r e - s p e c t i v e l y , w e r e a n a l y s e d assuming no change i n e v a p o t r a n s p i r a t i o n l o s s e s , t h e c o n c l u s i o n s w o u l d u n d e r e s t i m a t e t h e s t r e a m f l o w r e d u c t i o n caused b y t h e c l i m a t e change.

I n o t h e r cases, man's a c t i o n s a f t e r a c l i m a t e change may a c c e l e r a t e t h e c l i m a t e e f f e c t s and c r e a t e a d d i t i o n a l a d v e r s e e f f e c t s . T h e r e f o r e , i t i s v e r y i m p o r t a n t t o a c c o u n t f o r c l i m a t e v a r i a b i l i t y and man-induced catchment changes i n s e p a r a t e ways.

Man's i m p a c t o n t h e h y d r o l o g i c a l c y c l e can b e a r e s u l t o f b o t h man- i n d u c e d c l i m a t e changes o r man-induced changes i n catchment c h a r a c t e r i s t i c s . I n t h e p r e s e n t r e p o r t , however, t h e t e r m man's i n f l u e n c e on t h e h y d r o l o g i c a l c y c l e , w i l l o n l y r e f e r t o t h e e f f e c t s i n d u c e d b y catchment changes. F u r t h e r - more

,

when c o n s i d e r i n g t h e c l i m a t e ' s i n f l u e n c e on t h e h y d r o l o g i c a l c y c l e t.he p r e s e n t r e p o r t does n o t d i s t i n g u i s h between t h e e f f e c t s o f c l i m a t e v a r i a b i l i t y and c l i m a t e changes. Thus, t h i s r e p o r t i s r e s t r i c t e d i n scope t o d i s t i n g u i s h - i R g t h e i n f l u e n c e o f a r r o w A i n F i g . 1 . 2 . 1 f r o m a r r o w B.

1 . 3 C o n t e n t s o f t h e R e p o r t

I n a d d i t i o n t o t h i s i n t r o d u c t o r y , c h a p t e r , t h e r e p o r t c o n t a i n s f o u r main chap- t e r s and one appendix.

C h a p t e r 2 c o n t a i n s a b r i e f summary o f t h e proposed methodology, a b r i e f summary o f t h e s t a t e o f t h e a r t , and some recommendations r e g a r d i n g t h e need f o r f u t u r e a c t i v i t i e s w i t h i n t h i s f i e l d .

C h a p t e r 3 g i v e s an i n t r o d u c t i o n t o t h e v a r i o u s h y d r o l o g i c a l t o o l s w h i c h can b e u s e d f o r a s s e s s i n g t h e h y d r o l o g i c a l i m p a c t o f c l i m a t e and man's a c t i v i - t y . I n Chapter 4 a p r e s e n t a t i o n i s g i v e n o f t h e a p p r o p r i a t e s t a t i s t i c a l t e s t p r o c e d u r e s f o r t r e n d t e s t s . These c h a p t e r s do n o t p r e s e n t any new methods, and t h e y can b e seen as a n e c e s s a r y b a c k g r o u n d f o r C h a p t e r 5 ,

I n Chapter 5 t h e e s t a b l i s h e d methodology f o r d i s t i n g u i s h i n g between man's i n f l u e n c e and c l i m a t e i s d e s c r i b e d and d i s c u s s e d . Subsequently, t h e a p p l i c a - t i o n cjf t h i s methodology i s i l l u s t r a t e d i n t h e case s t u d i e s g i v e n i n Chapter 7 .

Thus, i n accordance w i t h t h e t e r m s o f r e f e r e n c e f o r t h e p r o j e c t t h e main r e p o r t i s p r i m a r i l y c o n f i n e d t o t h e e s t a b l i s h m e n t o f t h e methodology f o r d i s - t i n g u i s h i n g between t h e e f f e c t s G € man's i n f l u e n c e and c l i m a t e on t h e hydro- l o g i c a l c y c l e .

The methodology d e a l s w i t h t h e a n a l y s i s o f h i s t o r i c a l e f f e c t s as opposed t o t h e p r e d i c t i o n o f f u t u r e e f f e c t s . However, as t h e g l o b a l c l i m a t e changes become v e r y l i k e l y , t h e p r a c t i c a l i m p o r t a n c e o f b e i n g a b l e t o p r e d i c t t h e

(13)

changes i n w a t e r r e s o u r c e s a v a i l a b i l i t y as a consequence o f t h e c l i m a t e changes becomes c r u c i a l . T h e r e f o r e , an i n t r o d u c t i o n t o t h i s t o p i c i s g i v e n i n Appendix A, w h i c h c o n t a i n s a b r i e f i n t r o d u c t i o n t o knowledge r e g a r d i n g t h e

i n f l u e n c e o f g l o b a l c l i m a t e changes on w a t e r r e s o u r c e s . The r a p p o r t e u r s ex- p r e s s t h e i r a p p r e c i a t i o n t o D r . ' s Budyko and V i n n i k o v € o r p r e p a r i n g t h i s a p p e n d i x .

(14)

2 - 1

2. SUMMARY AND RECOMMENDATIONS

B o t h man's a c t i v i t y and c l i m a t e can h a v e a v e r y s i g n i f i c a n t e f f e c t on t h e hy- d r o i o g i c a l c y c l e . These e f f e c t s a r e i n c r e a s i n g g r e a t l y as a consequence o f t h e r a p i d i n c r e a s e i n p o p u l a t i o n , a g r i c u l t u r a l p r o d u c t i o n , and i n d u s t r i a l i z a t i o n .

I n c o n n e c t i o n w i t h t h e o n g o i n g r e s e a r c h a c t i v i t i e s o n t h e i n f l u e n c e o f g l o b a l c l i m a t e changes on w a t e r r e s o u r c e s , l o n g h i s t o r i c a l t i m e s e r i e s c a n b e a n a l y s e d and i n f e r e n c e s c a n b e made r e g a r d i n g c l i m a t e and i t s e f f e c t s on t h e h y d r o l o g i c a l r e g i m e . F o r t h i s p u r p o s e i t i s n e c e s s a r y t o b e a b l e t o d i s - t i n g u i s h between t h e e f f e c t s o f man's a c t i v i t y and o f c l i m a t e and hence t o i d e n t i f y and e l i m i n a t e t h e e f f e c t s o f man's a c t i v i t y .

2 . 1 Methodology

A methodology h a s been e s t a b l i s h e d f o r d i s t i n g u i s h i n g between t h e e f f e c t s o f man's a c t i v i t y and c l i m a t e on t h e h y d r o l o g i c a l c y c l e , i n p a r t i c u l a r s t r e a m f l o w and g r o u n d w a t e r . The methodology i s based o n j o i n t a p p l i c a t i o n o f s t a t i s t i c a l t e s t methods and r e g r e s s i o n o r d e t e r m i n i s t i c h y d r o l o g i c a l models. The methodo- l o g y i s i l l u s t r a t e d s c h e m a t i c a l l y i n F i g . 2 . 1 . 1 and e x p l a i n e d s t e p b y s t e p i n C h a p t e r 5.

A k e y e l e m e n t i n t h e m e t h o d o l o g y i s t h e p e r f o r m a n c e o f a s t a t i s t i c a l t r e n d t e s t u s i n g c l a s s i c a l h y p o t h e s i s - t e s t i n g p r o c e d u r e s . T y p i c a l l y , t h e n u l l h y p o t h e s i s , H i s t h a t t h e r e i s no t r e n d i n t h e p o p u l a t i o n f r o m w h i c h t h e d a t a were d r a w n . A s t e p t r e n d t e s t c a n b e u s e d i n case o f a sudden change. F o r t h i s case, t h e n o n - p a r a m e t r i c W i l c o x o n Rank-Sum t e s t i s recommended. A l t e r n a - t i v e l y , i n t h e case o f a g r a d u a l change, a m o n o t o n i c t r e n d t e s t c a n b e c a r r i e d o u t by use o f t h e n o n - p a r a m e t r i c Mann-Kendall t e s t .

0 '

The t e s t s can b e c a r r i e d o u t d i r e c t l y on t h e h y d r o l o g i c a l t i m e s e r i e s . However, t h i s approach does n o t d e a l w i t h t h e c o m p l i c a t i o n s a r i s i n g f r o m c l i - mate e f f e c t s on t h e h y d r o l o g i c a l t i m e s e r i e s . T h i s n a t u r a l v a r i a b i l i t y w i l l d e c r e a s e t h e power o f t h e s t a t i s t i c a l method t o d e t e c t t r e n d s , when t h e y do e x i s t , and when t r e n d s do n o t e x i s t , may r e s u l t i n f a l s e d e t e c t i o n o f t r e n d s t h a t a r e a r t i f a c t s o f t h e h i s t o r y o f c l i m a t i c c o n d i t i o n s d u r i n g t h e p e r i o d .

T h e r e f o r e , t h e recommended approach i n v o l v e s j o i n t use o f models and a s t a t i s t i c a l t r e n d t e s t i n g p r o c e d u r e . The model i s u s e d t o e x p l a i n t h e n a t u r a l f l u c t u a t i o n s i n t h e h y d r o l o g i c a l v a r i a b l e caused by t h e c l i m a t i c c o n d i t i o n s , and t h e s t a t i s t i c a l t r e n d t e s t i s a p p l i e d t o t h e r e m a i n i n g u n e x p l a i n e d v a r i a - b i l i t y . Three d i f f e r e n t model t y p e s may be u s e d f o r t h i s p u r p o s e , namely a s t a t i s t i c a l r e g r e s s i o n model, a lumped c o n c e p t u a l h y d r o l o g i c a l model, o r a d i s t r i b u t e d p h y s i c a l l y b a s e d h y d r o l o g i c a l model.

I f a h y d r o l o g i c a l m o d e l i s a p p l i e d i t m u s t b e a d e q u a t e l y v a l i d a t e d . The t r a d i t i o n a l l y a p p l i e d s p l i t - s a m p l e t e s t i s n o t s u f f i c i e n t f o r t h i s p u r p o s e . A ' h i e r a r c h i c a l scheme € o r s y s t e m a t i c t e s t i n g o f h y d r o l o g i c a l s i m u l a t i o n m o d e l s ' p r o p o s e d b y Klemes (1985) i s recommended.

(15)

STEP

I

2

STEP3

1

STEP4

i

STEP5

:

D a t a a v a i l a b l e b o t h b e f o r e and a f t e r d i s t u r b a n c e d a t a ?

N o model

'r'

S e l e c t i o n o f model t y p e

D i s t r i b u t e d based model

c

S t a t i s t i c a l t r e n d t e s t

-

s t e p t r e n d

- m o n o t o n i c t r e n d

D i s t r i b u t e d p h y s i c a l l y

-

s t e p t r e n d

-

m o n o t o n i c t r e n d

- e f f e c t s o f c l i m a t e

- e f f e c t s o f man's a c t i v i t y

- q u a l i t a t i v e c o n s i s t e n c y

- q u a n t i t a t i v e c o n s i s t e n c y

F i g . 2 . 1 . 1 S c h e m a t i z a t i o n o f t h e methodology.

I n t h e case o f a s t e p t r e n d t e s t two p e r i o d s a r e s e l e c t e d f o r t h e a n a l y - ses, namely a p e r i o d b e f o r e t h e e v e n t c a u s i n g t h e p o s s i b l e t r e n d o c c u r r e d

( r e f e r e n c e p e r i o d ) and a p e r i o d a f t e r t h i s e v e n t ( t e s t p e r i o d ) . The t w o samples a r e t h e n t e s t e d as t o w h e t h e r o r n o t t h e y can be assumed t o b e l o n g t o t h e same p o p u l a t i o n , i . e . t h a t no s i g n i f i c a n t change h a s o c c u r r e d . When a model i s used, i t i s c a l i b r a t e d a n d v a l i d a t e d on d a t a f r o m t h e t e s t p e r i o d and t h e s t a t i s t i c a l t e s t i s t h e n c a r r i e d o u t on t h e r e s i d u a l s ( o b s e r v e d v a l u e s minus simul.ated v a l u e s ) f r o m t h e model a p p l i e d t o b o t h t h e t e s t and r e f e r e n c e p e r i o d s .

I n t h e case o f a m o n o t o n i c t r e n d t e s t , o n l y one p e r i o d i s s e l e c t e d f o r t h e a n a l y s e s , and i t i s t h e n t e s t e d as t o w h e t h e r o r n o t a s t a t i s t i c a l l y s i g - n i f i c a n t t r e n d h a s o c c u r r e d . When a model i s used, t h e c a l i b r a t i o n and v a l i d a - t i o n m u s t n o t b e c a r r i e d o u t on t h e p e r i o d s e l e c t e d f o r t h e s t a t i s t i c a l t e s t . Hence c a l i b r a t i - o n an?. v a l i d a t i o n have t o b e c a r r i e d o u t o n a n o t h e r p e r i o d o r a l t e r n a t i v e l y u s i n g d a t a f r o m o t h e r b a s i n s and o b s e r v i n g t h e recommended v a l i - c l a t i o n p r o c e d u r e s .

(16)

2 - 3

A f t e r t h e s t a t i s t i c a l t r e n d t e s t f u r t h e r h y d r o l o g i c a l a n a l y s i s may i n some cases b e c a r r i e d o u t . The e x t e n t o f p o s s i b l e h y d r o l o g i c a l a n a l y s i s de- pends upon t h e s e l e c t e d m o d e l l i n g approach. I n t h e cases o f no model and r e - g r e s s i o n model no f u r t h e r a n a l y s i s i s p o s s i b l e . I n t h e case o f a lumped con- c e p t u a l model i t may b e p o s s i b l e t o e x p l a i n t h e d e t e c t e d changes q u a l i t a t i v e l y w i t h i n t h e framework o f t h e known human a c t i v i t i e s . I n t h e case o f a d i s t r i - b u t e d p h y s i c a l l y based model t h e e f f e c t s o f c l i m a t e and man's a c t i v i t y c a n b e e s t i m a t e d s e p a r a t e l y and t h e q u a n t i t a t i v e c o n s i s t e n c y o f t h e t e s t r e s u l t s may b e checked i n some cases, b y u t i l i z i n g t h e model t o p r e d i c t t h e e f f e c t s o f human a c t i v i t y and comparing t h i s w i t h t h e r e c o r d e d d a t a . As a n i n t e g r a t e d p a r t o f such f u r t h e r a n a l y s i s , s t a t i s t i c a l t r e n d t e s t s may i n some cases b e c a r r i e d o u t . A s p e c i a l case a r i s e s when a s t e p t r e n d t e s t h a s been s e l e c t e d but d a t a a r e o n l y a v a i l a b l e f o r t h e t e s t p e r i o d . I n t h i s case, a s t e p t r e n d t e s t i s s t r i c t l y n o t v a l i d . However, i n some cases, i t i s p o s s i b l e t o e s t i m a t e t h e e f f e c t s o f c l i m a t e and man's a c t i v i t y and t o a n a l y z e w h e t h e r a s i g n i f i c a n t t r e n d (caused by man's a c t i v i t y ) between t h e r e f e r e n c e and t h e t e s t p e r i o d s w o u l d have been d e t e c t e d , i f d a t a h a d e x i s t e d a l s o f o r t h e r e f e r e n c e p e r i o d .

The methodology i s i l l u s t r a t e d by t w o case s t u d i e s .

2 . 2 S t a t e o f t h e A r t

O n l y v e r y few s t u d i e s f o c u s s i n g e x p l i c i t l y o n t h e d i s t i n g u i s h i n g between m a n ' s i n f l u e n c e and c l i m a t e e f f e c t s have been r e p o r t e d . However, i n a g r e a t number o f a n a l y s e s man-induced changes as w e l l as c l i m a t e v a r i a b i l i t y h a v e b e e n i n c l u d e d , Hence, a c o n s i d e r a b l e e x p e r i e n c e e x i s t s o n t h e s u b j e c t .

As t h e methodology i s new and appears as a n i n t e g r a t i o n o f s t a t i s t i c a l methods and h y d r o l o g i c a l m o d e l l i n g , w h i c h t r a d i t i o n a l l y a r e a p p l i e d s e p a r a t e - l y , n o s t u d i e s , t o t h e a u t h o r s ' knowledge, e x i s t , w h i c h f o l l o w s t r i c t l y t h e e s t a b l i s h e d methodology.

However, t h e d i f f e r e n t e l e m e n t s i n t h e methodology a r e g e n e r a l l y s c i e n t i - f i c a l l y w e l l p r o v e n and w i d e s p r e a d f o r p r a c t i c a l a p p l i c a t i o n s . The o n l y excep- t i o n i s t h a t v a l i d a t i o n o f h y d r o l o g i c a l models a r e n o t a l w a y s c a r r i e d o u t o n a s c i e n t i f i c a l l y sound b a s i s . T h i s i s becoming i n c r e a s i n g l y i m p o r t a n t e s p e c i a l l y w i t h r e g a r d t o t h e advanced d i s t r i b u t e d p h y s i c a l l y based models, w h i c h a r e o f t e n c l a i m e d t o b e a b l e t o p r e d i c t a l m o s t a n y t h i n g . I n t e r n a t i o n a l l y a c c e p t e d p r o c e d u r e s f o r m o d e l v a l i d a t i o n a r e r e q u i r e d .

2.3 Recommendations

( a ) The methodology e s t a b l i s h e d i n t h i s r e p o r t h a s been t e s t e d o n t w o case s t u d i e s by u s i n g e x i s t i n g r e s u l t s from o t h e r p r e v i o u s s t u d i e s a v a i l a b l e t o t h e a u t h o r s . However, t h e s e p r e v i o u s s t u d i e s d i d n o t c o m p l e t e l y a l l o w f o r a s t r i c t a p p l i c a t i o n o f t h e m e t h o d o l o g y , and an e x t e n s i o n o f t h e s e s t u d i e s was o u t s i d e t h e scope o f t h e p r e s e n t p r o j e c t . T h e r e f o r e , i t i s recommended t h a t t h e methodology b e f u r t h e r a p p l i e d and d e v e l o p e d i n t e r - n a t i o n a l l y d u r i n g t h e coming y e a r s . Research p r o j e c t s s h o u l d b e e s t a b - l i s h e d w i t h t h i s purpose i n c o n n e c t i o n w i t h comprehensive case s t u d i e s where t h e e f f e c t s o f man's a c t i v i t y and c l i m a t e a r e n o t g e n e r a l l y a g r e e d upon b e f o r e h a n d .

(17)

( b ) The p r e s e n t methodology i s l i m i t e d i n scope t o d i s t i n g u i s h between t h e e f f e c t s o f c l i m a t e and t h o s e o f changes i n catchment c h a r a c t e r i s t i c s . Thus no d i s t i n g u i s h m e n t i s made between man-induced c1imat.e changes and n a t u r a l l y caused c l i m a t e changes. I t i s recommended t h a t t h e methodology be e x t e n d e d s o t h a t t h e d i s t i n g u i s h i n g , c a l l e d f o r i n t h e t e r m s o f r e f e - r e n c e

,

between t h e e f f e c t s o f man's a c t i v i t y and " c l i m a t e v a r i a b i l i t y "

a l s o i n c l u d e t h e e f f e c t o f man's a c t i v i t y t h r o u g h c l i m a t e changes and i n t e r p r e t t h e t e r m " c l i m a t e v a r i a b i l i t y " as t h e n a t u r a l c l i m a t e .

( c ) The d i s t r i b u t e d , p h y s i c a l l y b a s e d models s h o u l d b e t e s t e d i n t e r n a t i o n a l l y on t h e b a s i s o f comprehensive v a l i d a t i o n p r o c e d u r e s . Thus, an i n t e r c o m p a - r i s o n o f s e v e r a l o f t h e s e models on t h e i r a b i l i t y t o p r e d i c t r u n o f f f r o m unqauged catchments, t o p r e d i c t t h e e f f e c t s o f changed c l i m a t i c c o n d i - t i o n s and t o p r e d i c t t h e e f f e c t s o f v a r i o u s k i n d s o f man's a c t i v i t y ( e . g . l a n d u s e change and g r o u n d w a t e r development) s h o u l d be c a r r i e d o u t under t h e management o f an i n t e r n a t i o n a l o r g a n i z a t i o n .

(d) F u r t h e r i n s i g h t on t h e e f f e c t s o f catchment changes on t h e h y d r o l o g i c a l c y c l e v e r s u s t h e e f f e c t s o f c l i m a t e may b e g a i n e d by a n a l y z i n g t h e r e - s u l t s o f t r e n d a n a l y s e s a p p l i e d t o s e v e r a l catchments w i t h i n a p a r t i c u l a r r e g i o n . I t i s recommended t h a t t h i s b e done f o r s e l e c t e d r e g i o n s . F o r example, i n many cases, one may e x p e c t t h a t t r e n d s due t o c l i m a t e e f f e c t s w o u l d b e d i s p l a y e d more c o n s i s t e n t l y o v e r a r e g i o n t h a n t h o s e due t o catchment changes.

(18)

3-1

3. HYDROLOGICAL TOOLS

3 . 1 I n t r o d u c t i o n

I n t h i s c h a p t e r an i n t r o d u c t i o n i s g i v e n t o t h e h y d r o l o g i c a l t o o l s w h i c h can be a p p l i e d t o assess t h e i m p a c t o f c l i m a t e and t h e i m p a c t o f man's a c t i v i t y o n t h e h y d r o l o g i c a l c y c l e , i n p a r t i c u l a r s t r e a m f l o w and groundwater. I t i s n o t i n t e n d e d t o g i v e v e r y d e t a i l e d d e s c r i p t i o n s of t h e v a r i o u s t o o l s o r methods but t o g i v e more fundamental d e s c r i p t i o n s t o g e t h e r w i t h a d i s c u s s i o n o f t h e a p p l i c a b i l i t y and l i m i t a t i o n s o f t h e d i f f e r e n t methods p r e s e n t l y a v a i l a b l e . F o r more d e t a i l e d d e s c r i p t i o n , r e f e r e n c e s a r e g i v e n t o t h e l i t e r a t u r e .

The a v a i l a b l e h y d r o l o g i c a l methods a p p l i c a b l e f o r t h e p r e s e n t p u r p o s e c a n b a s i c a l l y b e c l a s s i f i e d i n t w o groups, namely t h e d e t e r m i n i s t i c methods and t h e s t a t i s t i c a l methods.

3.2 D e t e r m i n i s t i c Models

D e t e r m i n i s t i c methods i n h y d r o l o g y i n p r a c t i c e r e f e r t o m a t h e m a t i c a l d e t e r m i - n i s t i c models, o f t e n s i m p l y d e n o t e d as h y d r o l o g i c a l models.

I n p r i n c i p l e , a h y d r o l o g i c a l model i s a s i m p l i f i e d q u a n t i t a t i v e d e s c r i p - t i o n o f ( p a r t s o f ) t h e h y d r o l o g i c a l c y c l e . A h y d r o l o g i c a l m o d e l may b e a v e r y s i m p l e f o r m u l a , o r i t may b e a v e r y comprehensive and c o m p l i c a t e d computer- based m a t h e m a t i c a l model.

The f u n d a m e n t a l b a s i s f o r t h e d e t e r m i n i s t i c d e s c r i p t i o n o f t h e h y d r o l o g i - c a l p r o c e s s e s i s a c o n t i n u i t y e q u a t i o n ( c o n s e r v a t i o n o f mass) and a f l o w equa- t i o n ( c o n s e r v a t i o n of momentum). These e q u a t i o n s t a k e d i f f e r e n t f o r m s € o r t h e d i f f e r e n t p r o c e s s e s . The c o n t i n u i t y e q u a t i o n i s o f t e n f o r m u l a t e d as a w a t e r b a l a n c e e q u a t i o n :

P = E

+

Q

+

A

+

AS

where

P = p r e c i p i t a t i o n E = e v a p o r a t i o n Q = r u n o f f

A = w a t e r a b s t r a c t i o n f r o m t h e catchment minus a d d i t i o n a l w a t e r AS = w a t e r s t o r a g e a t t h e end minus s t o r a g e a t t h e b e g i n n i n g o f t h e

i n f l o w t o t h e catchment due t o man's a c t i v i t y t i m e s t e p

The w a t e r b a l a n c e e q u a t i o n i s v a l i d f o r catchments u n d e r t h e a s s u m p t i o n t h a t t h e t o p o g r a p h i c a l and g r o u n d w a t e r d i v i d e s c o i n c i d e .

(19)

The i n p u t P-E t o t h e catchment e q u a l s t h e o u t p u t Q+A p l u s t h e i n c r e a s e o f s t o r a g e A S . T h i s A S , w h i c h e x p r e s s e s t h e n o n - s t e a d y c h a r a c t e r o f t h e f l o w p r o - c e s s , c a n sometimes be n e g l e c t e d w h e n t h e w a t e r b a l a n c e e q u a t i o n i s a p p l i e d t o l o n g t i m e i n t e r v a l s .

T h e w a t e r b a l a n c e method has been u s e d e x t e n s i v e l y d u r i n g t h e p a s t deca- des f o r v a r i o u s p u r p o s e s i n c l u d i n g some a p p l i c a t i o n s f o r s t u d y i n g t h e i m p a c t o f m a n ' s a c t i v i t y on t h e h y d r o l o g i c a l c y c l e . As t h e method i s v e r y easy t o use and o n l y r e q u i r e s few d a t a , i t can be u s e d f o r an i n i t i a l s c r e e n i n g o f t h e d a t a .

I n a d d i t i o n t o t h e w a t e r b a l a n c e methods, t h e d e t e r m i n i s t i c models o f p a r t i c u l a r i n t e r e s t a r e t h o s e w h i c h a r e a b l e t o s i m u l a t e ( p a r t o f ) t h e l a n d phase o f t h e h y d r o l o g i c a l c y c l e o v e r a l o n g p e r i o d o f t i m e ( s e v e r a l y e a r s ) .

I n t h e s e models, t h e catchment c h a r a c t e r i s t i c s i n c l u d i n g t h e man-induced changes o f l a n d u s e and w a t e r development a r e r e p r e s e n t e d somehow i n t h e model p a r a m e t e r s , w h i l e t h e c l i m a t i c v a r i a b l e s a r e t h e m a i n input d a t a (e.g. meteo- r o l o g i c a l t i m e s e r i e s ) . I n t h i s way, a change i n t h e catchment c h a r a c t e r i s t i c s and a change o r v a r i a b i l i t y i n t h e c l i m a t e a r e r e p r e s e n t e d i n s e p a r a t e ways i n t h e s i m u l a t i o n o f t h e h y d r o l o g i c a l c y c l e . A s d i s c u s s e d b e l o w , t h i s f a c t i s v e r y i m p o r t a n t f o r a p p l i c a t i o n o f t h e h y d r o l o g i c a l models f o r t h e p r e s e n t pur- pose.

D e t e r m i n i s t i c models c a n b e c l a s s i f i e d a c c o r d i n g t o whether t h e model g i v e s a lumped o r a d i s t r i b u t e d d e s c r i p t i o n o f t h e c o n s i d e r e d a r e a , and w h e t h e r t h e d e s c r i p t i o n o f t h e h y d r o l o g i c a l p r o c e s s e s i s e m p i r i c a l , concep- t u a l , o r more p h y s i c a l l y based. A s most c o n c e p t u a l models a r e a l s o lumped and as m o s t p h y s i c a l l y based models a r e a l s o d i s t r i b u t e d , t h e f o l l o w i n g t h r e e m a i n g r o u p s o f d e t e r m i n i s t i c models emerge:

o E m p i r i c a l models ( b l a c k b o x )

o Lumped, c o n c e p t u a l models ( g r e y b o x )

0 D i s t r i b u t e d , p h y s i c a l l y b a s e d models ( w h i t e b o x )

B l a c k b o x models a r e e m p i r i c a l , i n v o l v i n g a m a t h e m a t i c a l e q u a t i o n t h a t has been assessed, n o t f r o m t h e p h y s i c a l p r o c e s s e s i n t h e catchment, b u t from ana- l y s e s of c o n c u r r e n t input and o u t p u t t i m e s e r i e s .

P r o b a b l y , t h e h e s t known b l a c k b o x models i n h y d r o l o g y a r e t h e u n i t hy- d r o g r a p h model and models a p p l y i n g t h e u n i t h y d r o g r a p h p r i n c i p l e s , c f . Sherman

( 1 9 3 2 ) and Nash ( 1 9 5 9 ) .

The b l a c k b o x models have been d e v e l o p e d and e x t e n s i v e l y a p p l i e d b e f o r e t h e computer t e c h n o l o g y made i t p o s s i b l e t o use more p h y s i c a l l y c o r r e c t ( a n d t h u s more complex) models. Today, b l a c k box p r i n c i p l e s a r e o f t e n u s e d i n some components o f a l a r g e r model, e.g. t h e u n i t h y d r o g r a p h i s o f t e n used f o r s t r e a r n f 1.0w r o u t i r ~ q i n c o n c e p t u a l r a i n f a l l - r u n o f f models.

The s t a t i s t i c a l r e g r e s s i o n models w h i c h may b e u t i l i z e d as d e t e r m i n i s t i c t r a n s f e r f u n c t i o n models can a l s o h e c a t e g o r i z e d as e m p i r i c a l models, c f . Sec- t i o n 3 . 3 .

(20)

3-3

Lumped, c o n c e p t u a l models o p e r a t e w i t h d i f f e r e n t and m u t u a l l y i n t e r r e l a t e d s t o r a g e s r e p r e s e n t i n g p h y s i c a l e l e m e n t s i n t h e catchment. The mode o f opera- t i o n may b e c h a r a c t e r i z e d as a b o o k k e e p i n g system c o n t i n u o u s l y a c c o u n t i n g € o r t h e m o i s t u r e c o n t e n t s i n t h e s t o r a g e s .

M e t e o r o l o q i c a l I n p u t

-

-

- - - - -

I n t e r c e p t i o n Storage

w:

Input-Output

cl 1-1

Storage

/ 7

P r o c e s s Evapotrans -

7""

p i r a t i o n

Overland F l o w I n f i l t r a t i o n

I I

upper Zone Storage

- 1

I I

Channel

Simulated Streamf l o w

F i g . 3 . 2 . 1 S t r u c t u r e o f t h e S t a n f o r d Watershed Model, s i m p l i f i e d a f t e r C r a w f o r d and L i n s l e y ( 1 9 6 6 ) .

Due t o t h e lumped d e s c r i p t i o n , where a l l p a r a m e t e r s and v a r i a b l e s r e p r e - s e n t average v a l u e s o v e r t h e e n t i r e catchment, t h e d e s c r i p t i o n o f t h e h y d r o l o - g i c a l p r o c e s s e s cannot b e b a s e d d i r e c t l y on t h e e q u a t i o n s v a l i d f o r i n d i v i d u a l s o i l columns. Hence, t h e e q u a t i o n s a r e s e m i - e m p i r i c a l , but w i t h a p h y s i c a l b a s i s . T h e r e f o r e , t h e model p a r a m e t e r s cannot u s u a l l y b e assessed f r o m f i e l d d a t a , b u t have t o b e o b t a i n e d t h r o u g h c a l i b r a t i o n .

The S t a n f o r d Model ( C r a w f o r d and L i n s l e y (1966)

,

t h e s t r u c t u r e o f w h i c h i s s c h e m a t i c a l l y shown i n F i g . 3 . 2 . 1 , i s c e r t a i n l y t h e b e s t known w a t e r s h e d model o f t h e l u m p e d , c o n c e p t u a l t y p e .

(21)

D u r i n g t h e decade f o l . l o w i n g t h e development o f t h e S t a n f o r d Model s e v e r a l o t h e r models o f t h e same t y p e w e r e developed, c f . F l e m i n g ( 1 9 7 5 ) a n d Kuchment (1980) f o r r e v i e w s . B e i n g g e n e r a l p u r p o s e r a i n f a l l - r u n o f f models, many o f t h e s e models a r e t o d a y a p p l i e d on an o p e r a t i o n a l b a s i s f o r a v a r i e t y o f pur- poses.

I t s h o u l d b e emphasized t h a t n o t a l l models s t r i c t l y f i t i n t o t h e above t h r e e g r o u p s o f models. Many models f a l l i n between a c o n c e p t u a l and a phy- s i c a l l y b a s e d approach. Some o f t h e c o n c e p t u a l models a r e s e m i - d i s t r i b u t e d i n t h e sense t h a t subareas w i t h t h e same h y d r o l o g i c a l c h a r a c t e r i s t i c s (e.g. p r e - c i p i t a t i o n

,

t e m p e r a t u r e

,

s o i l

,

v e g e t a t i o n

,

and s l o p e ) a r e grouped t o g e t h e r t o f o r m h y d r o l o g i c a l r e s p o n s e u n i t s . The G G I - 8 5 model (Vinogradov, 1 9 8 5 ; and V u g l i n s k y , 1987) i s an example o f such a model t y p e .

The p r i n c i p a l mode o f o p e r a t i o n o f a d i s t r i b u t e d , p h y s i c a l l y b a s e d model i s i l l u s t r a t e d i n F i g . 3 . 2 . 2 .

C o n t r a r y t o t h e l u m p e d , c o n c e p t u a l models, a d i s t r i b u t e d , p h y s i c a l l y based model does n o t c o n s i d e r t h e w a t e r f l o w s i n a catchment t o t a k e p l a c e between a f e w s t o r a g e s . I n s t e a d , t h e f l o w s o f w a t e r and energy a r e d i r e c t l y c a l c u l a t e d f r o m t h e g o v e r n i n g d i f f e r e n t i a l e q u a t i o n s

,

f o r i n s t a n c e t h e S a i n t Venant e q u a t i o n s f o r o v e r l a n d f l o w , R i c h a r d s ’ e q u a t i o n f o r u n s a t u r a t e d zone

f l o w , and B o u s s i n e s q ’ s e q u a t i o n f o r g r o u n d w a t e r f l o w .

The d i s t r i b u t e d , p h y s i c a l l y b a s e d models g i v e a d e t a i l e d and p o t e n t i a l l y more c o r r e c t d e s c r i p t i o n o f t h e h y d r o l o g i c a l p r o c e s s e s i n t h e catchment t h a n do t h e o t h e r model t y p e s . T h e r e f o r e , t h e y h a v e p o t e n t i a l l y more f i e l d s o f a p p l i c a t i o n as d i s c u s s e d b e l o w . O f c o u r s e , due t o t h e c o m p l e x i t y o f t h e c a t c h - ment i t w i l l n e v e r i n p r a c t i c e b e p o s s i b l e t o o b t a i n s u f f i c i e n t d a t a t o g i v e a

f u l - l y c o r r e c t s i m u l a t i o n i n a l l d e t a i l s .

A f i r s t a t t e m p t t o o u t l i n e t h e p o t e n t i a l s and some o f t h e e l e m e n t s i n a d i s t r i b u t e d , p h y s i c a l l y based model was made b y F r e e z e and H a r l a n ( 1 9 6 9 ) . Today, s e v e r a l p h y s i c a l l y based models t r e a t i n g o n l y s i n g l e h y d r o l o g i c a l p r o - cesses have been d e v e l o p e d and e x t e n s i v e l y a p p l i e d . A l m o s t a l l groundwater models € o r i n s t a n c e a r e o f t h e d i s t r i b u t e d , p h y s i c a l l y b a s e d t y p e . Examples o f models c o v e r i n g t h e e n t i r e l a n d phase o f t h e h y d r o l o g i c a l c y c l e a r e r e p o r t e d b y Weeks e t a l . ( 1 9 7 4 ) , Wardlaw ( 1 9 7 8 ) , R e f s g a a r d and Hansen ( 1 9 8 2 ) . These mo- d e l s a r e g e n e r a l l y s p e c i f i c p u r p o s e models w i t h a lumped, c o n c e p t u a l d e s c r i p - t i o n o f t h o s e p r o c e s s e s t h a t a r e l e s s i m p o r t a n t f o r t h e i r p a r t i c u l a r a p p l i c a - t i o n . T h e SHE model ( A b b o t t e t a l . 1986; Storm, 1 9 8 6 ) , t h e I H D M model ( M o r r i s , 1980, Rogers e t a l . 1985) and t h e model d e s c r i b e d by Kuchment e t a l . (1983) a r e some o f t h e few more g e n e r a l p u r p o s e m o d e l l i n g systems w h i c h a r e a p p l i - c a b l e under a w i d e v a r i e t y o f h y d r o l o g i c a l and h y d r o g e o l o g i c a l c o n d i t i o n s .

(22)

3- 5

E V A P O T R A N S P I R A T I O N M O D E L

I 1 1 I I

Evaporation f r o m T r a n s p i r a t i o n Evaporation Irom Sublimation I r o m

Intercepted R a i n Soil Surlaces Snow P a c k lrom ground

f

t

and Snow

R a i n . S n o w , V a p o u r

I ( n

KEY.

F i g . 3 . 2 . 2 Schematic d i a g r a m o f a w a t e r s h e d and a q u a s i t h r e e - d i m e n s i o n a l d i s t r i b u t e d p h y s i c a l l y based model o f t h e w a t e r s h e d ( t h e SHE model, c f . S t o r m ( 1 9 8 6 ) ) .

3.2.4 S e l e c t i o n o f a p p r o p r i a t e model t y p e

...

A l a r g e number o f h y d r o l o g i c a l models e x i s t s o f w h i c h many a r e f u n c t i o n i n g f u n d a m e n t a l l y i n t h e same way. F o r i n s t a n c e , a t l e a s t 2 0 d i f f e r e n t r a i n f a l l - r u n o f f models o f t h e lumped, c o n c e p t u a l t y p e e x i s t . A l t h o u g h t h e s e models a t a f i r s t g l a n c e may l o o k v e r y d i f f e r e n t , f u n d a m e n t a l l y t h e y have t h e same s t r u c - t u r e and a r e b a s i c a l l y f u n c t i o n i n g a l o n g t h e same p r i n c i p l e s .

Thus, t h e q u e s t i o n " w h i c h model i s most a p p r o p r i a t e f o r a p a r t i c u l a r h y d r o l o g i c a l p r o b l e m ? " c a n n o t b e answered s t r i c t l y b y g i v i n g t h e name o f one model. I n s t e a d , a g e n e r a l d i s c u s s i o n w i l l b e g i v e n on t h e a p p r o p r i a t e n e s s o f t h e above m e n t i o n e d model t y p e s f o r t h e d i f f e r e n t k i n d s o f h y d r o l o g i c a l p r o - blems.

The e m p i r i c a l models a r e g e n e r a l l y o f i n t e r e s t as s i n g l e e v e n t models o r as subcomponents o f more c o m p l i c a t e d models. The e m p i r i c a l models d i r e c t l y a p p l i c a b l e f o r t h e p r e s e n t p u r p o s e a r e t h e s t a t i s t i c a l r e g r e s s i o n models, (see S e c t i o n 3 . 3 ) .

The lumped, c o n c e p t u a l models a r e e s p e c i a l l y w e l l s u i t e d f o r s i m u l a t i o n o f t h e r a i n f a l l - r u n o f f p r o c e s s when h y d r o l o g i c a l t i m e s e r i e s e x i s t t h a t a r e s u f f i c i e n t l y l o n g f o r a model c a l i b r a t i o n o r d a t a e x i s t f o r r e g i o n a l i z a t i o n o f model p a r a m e t e r s . Thus, t y p i c a l f i e l d s o f a p p l i c a t i o n a r e :

(23)

o E x t e n s i o n o f s h o r t s t r e a m f l o w r e c o r d s based o n l o n g r a i n f a l l r e c o r d s . o R e a l - t i m e r a i n f a l l - r u n o f f s i m u l a t i o n e.g. f o r f l o o d f o r e c a s t i n g .

The lumped, c o n c e p t u a l models a r e o f i n t e r e s t i n t h e p r e s e n t c o n t e x t f o r t h e i r a b i l i t y t o s i m u l a t e t h e e f f e c t s o f c l i m a t e on s t r e a m f l o w .

The d i s t r i b u t e d , p h y s i c a l l y based models can i n p r i n c i p l e b e a p p l i e d t o a l m o s t any k i n d o f h y d r o l o g i c a l p r o b l e m . Some examples o f t y p i c a l a p p l i c a t i o n s a r e :

o P r e d i c t i o n o f t h e e f f e c t s o f catchment changes due t o human i n t e r f e r e n c e i n t h e h y d r o l o g i c a l c y c l e , such as changes i n l a n d use, u r b a n i z a t i o n , g r o u n d w a t e r development, o r i r r i g a t i o n . S i n c e p a r a m e t e r s o f t h e model t e n d t o b e more p h y s i c a l l y based, t h e change i n p a r a m e t e r v a l u e s c o r r e - s p o n d i n g t o t h e catchment changes can sometimes b e e s t i m a t e d d i r e c t l y .

0 P r e d i c t i o n o f r u n o f f f r o m ungauged catchments and f r o m catchments w i t h r e l a t i v e l y s h o r t r e c o r d s . A s opposed t o t h e lumped, c o n c e p t u a l models, w h i c h r e q u i r e l o n g h i s t o r i c a l t i m e s e r i e s o f r a i n f a l l , r u n o f f , and eva- p o r a t i o n d a t a f o r t h e p a r a m e t e r assessment, t h e p a r a m e t e r s o f t h e d i s t r i - b u t e d , p h y s i c a l l y b a s e d models may be assessed d i r e c t l y f r o m i n t e n s i v e , s h o r t - t e r m f i e l d i n v e s t i g a t i o n s .

0 K a t e r q u a l i t y and s o i l e r o s i o n m o d e l l i n g f o r w h i c h a more d e t a i l e d and p h y s i c a i l y c o r r e c t s i m u l a t i o n o f w a t e r f l o w s i s i m p o r t a n t .

The m a i n p r o b l e m s u s u a l l y m e n t i o n e d i n c o n n e c t i o n w i t h t h e a p p l i c a t i o n o f d i s t r i b u t e d , p h y s i c a l l y based models a r e :

a) L a r g e reyui.rements o f d a t a , e s p e c i a l l y t h o s e d e s c r i b i n g m e t e o r o l o g y , geo- I.ogy, s o i l , and v e g e t a t i o n .

b ) I n s u f f i c i e n t knowledge o f t h e p h y s i c s o f t h e h y d r o l o g i c a l p r o c e s s e s w h i c h a r e m o d e l l e d i n q r e a t d e t a i l .

c ) S c a l e p r o b l e m s when e x t e n d i n g t h e p r o c e s s d e s c r i p t i o n f r o m a s i n g l e p o i n t t o an e n t i r e catchment.

d) L a r g e computer r e q u i r e m e n t s .

The d i s t r i b u t e d , p h y s i c a l l y b a s e d models a r e a b l e d i r e c t l y t o u t i l i z e t h e d i s t r i b u t e d i n f o r m a t i o n u s u a l l y a v a i l a b l e i n t o p o g r a p h i c a l

,

g e o l o g i c a l

,

and s o i l maps and o t h e r r e m o t e l y sensed i n f o r m a t i o n , i n c l u d i n g c o n t i n u o u s u p d a t i n g o f catchment. c o n d i t i o n s (e.g. snow c o v e r ) . Thus, t h e d a t a r e q u i r e m e n t s U - s u a l l y l i s t e d f o r t h e s e models a r e huge, b u t t h i s m e r e l y r e f l e c t s t h a t t h e models can u t i l i z e a l l . o f t h e s e d a t a , i f t h e y a r e made a v a i l - a b l e . O n t h e o t h e r hand, t h e models can b e o p e r a t e d with l e s s d a t a a v a i l a b l - e , i n w h i c h case t h e p r e d i c t e d r e s u l t s w i . 1 1 I3e more u n c e r t a i n u n l e s s a c a l i b r a t i o n i s p o s s i b l e .

S i m i l a r l y , w i t h r e s p e c t t o t h e argument t h a t t h e r e s t i l l i s an i n s u f f i - c i e n t knowledge o f t h e h y d r o l o g i c a l p r o c e s s

,

p r o p o n e n t s o f p h y s i c a l l y based models m t e t h a t a c o m p a r a t i v e l y l a r g e r p a r t o f t h e e x i s t i n g knowledge can h e b u i l t i n t o t h e s e m o d e l s

,

t h a n i n t o t-he lumped, c o n c e p t u a l models.

Références

Documents relatifs

In contrast however, the video stills, together with the voice and sound transcripts, especially in The Watch Man, constitute an excellent choice to dislocate

(Photo WHO ) Right : This housewif e in the Yucatan peninsu- la takes for granted the fact that the plants gro wing around her home have medicinal uses. Th e study of

Sometimes danger- ous products from industry, agriculture and other human activities enter the rivers, lakes, oceans and underground water, and can contaminate our

Of course, I do not have the same energy as before, I feel more tired, and I am full of new aches and pains, but I have difficulty perceiving that I have aged?. And I

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des

Somehow, this situation was similar to the three years that passed from the 1984 El País front cover to Agustí and Moyà-Solà’s article in 1987, when information about the famous

guno en proceder al cambio, espero recibir instrucciones para ocuparme del asunto con la antelación suficiente, para que esté ter¬. minado el dia de la inauguración de

A rich property hierarchy, property characteristics and sub-property chains is used in order to maximise the number of entailments on an individual from the fewest possible