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FRIEND 2002

FRIEND – a global

perspective 1998-2002

Edited by Alan Gustard and Gwyneth A. Cole

Centre for Ecology and HydrologyWallingford UK United Nations Educational, Scientific and Cultural Organisation

International Hydrological Programme V

FRIEND — Flow Regimes from International Experimental and Network Data

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British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library

United Nations Educational, Scientific and Cultural Organisation International Hydrological Programme V

Hydrology and water resources for sustainable development in a changing environment Project 1.1 Application of methods of hydrological analysis using regional data sets

FRIEND — Flow Regimes from International Experimental and Network Data

© Copyright CEH 2002 ISBN 1 903741 03 3

Published by the Centre for Ecology and Hydrology, Wallingford, UK in cooperation with the FRIEND Intergroup Coordinating Committee on behalf of UNESCO

February 2002

This report was prepared at CEH Wallingford on behalf of UNESCO. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, or otherwise, without the prior permission of the copyright owner, the Centre for Ecology and Hydrology, Crowmarsh Gifford, Wallingford, Oxon, OX10 8BB, UK.

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FRIEND 2002

Foreword

The origin of FRIEND goes back to the International Hydrological Decade (IHD), which launched a large number of representative and experimental basins, underpinned mostly by national financial support. In retrospect, the IHD was a highly visionary programme, which now provides the longer-term data sets for assessing the hydrological impacts of climatic variability and land-use change. At the time the IHD was launched, neither climate change nor global change were commonly part of the scientific vocabulary.

With the launch of FRIEND as a contribution to UNESCO’s Third International Hydrological Programme (IHP-III) from 1984-1988, the initial focus was on the data-rich basins of north- west Europe (Northern European FRIEND). Various techniques were established, ranging from statistical methods to conceptual and physical models, for assessing the regional hydrological behaviour of flow regimes. The end of this first phase was marked by the

“FRIENDS in Hydrology” Conference in Bolkesjø, Norway in April 1989, the publication of Conference proceedings in the IAHS Series of Proceedings and Reports (Red Books) and a two-volume report on FRIEND. This started a long partnership between FRIEND and the International Association of Hydrological Sciences (IAHS), which continues today through sponsorship of conferences and publication of reports.

In its second phase (1989-1993), as project H-5-5 in IHP-IV, FRIEND expanded geographically.

With the support of Cemagref (La recherche pour l’ingénierie de l’agriculture et de l’environnement) in France, FRIEND became established in the Alpine and Mediterranean (AMHY) region, and later in west and central Africa (AOC: Afrique de l’Ouest et Centrale) and in southern Africa in collaboration with SADC, the Southern African Development Community.

Even at this stage, FRIEND scientific groups had made a unique contribution by their impact on the policy of national governments towards the international exchange of hydrological data. Until then political considerations had not encouraged such exchanges, but FRIEND now provided the means by which this could be achieved.

During the third (1994-1997) and fourth (1998-2001) phases, FRIEND has made a major contribution to the fifth International Hydrological Programme (1996-2001) as Project 1.1 and has progressively diffused into other regions. Asian Pacific FRIEND, Nile FRIEND, Hindu Kush/Himalayan (HKH) FRIEND and FRIEND/AMIGO for Mesoamerica and the Caribbean have all been established. Over 100 countries now participate in FRIEND within eight regional FRIEND groups. Further expansion is expected, with the possibility of establishing FRIEND in Mesopotamia, Central Asia and the Andes, the last of these in cooperation with the International Commission on Snow and Ice (ICSI) of IAHS.

In recognition of the expansion of this project, and its ever-enlarging network, the 14th Session of the IHP Intergovernmental Council, in June 2000, approved the elevation of FRIEND to a stand-alone cross-cutting theme within IHP-VI (2002-2007).

A significant feature of FRIEND is the impressive list of publications that have emerged in refereed scientific journals, and these are summarised in the current and previous FRIEND reports. FRIEND has been a ‘flag-carrier’ for the IHP in maintaining a high level of ‘cutting edge’ science. The brief to maintain a core scientific focus will continue in answer to concerns that the technical focus of FRIEND could be diluted by its new cross-cutting position within IHP-VI. As with the contiguous cross-cutting HELP (Hydrology for Environment, Life and Policy) Project in IHP-VI, the ability to undertake good science linked with practical land- water management issues is not a contradiction. FRIEND is now in a position whereby it

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should be encouraged to impact on the water policy of national governments through the conveyance of technical outputs where they are most needed. For example, poverty alleviation linked with the technical outputs of the Low Flow groups will secure a better understanding (and supply) of water during seasonal and inter-annual drought.

In IHP-VI, FRIEND is now sufficiently mature to begin interfacing with other IHP technical projects, notably groundwater and ecohydrology, as well as supporting selected HELP basins as part of the scientific assessment and inventory of water resources to define the appropriate experimental hydrology response. Steps are now being taken to establish an intrascientific expert group to advise how best to interface between these various disciplines and projects during IHP-VI.

In conclusion, I would like to express my thanks to all the hydrologists, regional coordinators and national governments who have provided the necessary financial support to ensure the success of the FRIEND project. In particular, I thank Alan Gustard (Coordinator of NE FRIEND) and Gwyneth Cole, both of the Centre for Ecology and Hydrology, Wallingford, UK, who have compiled and edited this report on behalf of the FRIEND Regional Groups as a contribution towards the 4th International FRIEND Conference “Bridging the gap between research and practice” in Cape Town, 18-22 March 2002.

M. Bonell Chief of Section: Hydrological Processes and Climate UNESCO Division of Water Sciences 6 November 2001

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FRIEND 2002

Contents

Acknowledgements ix

Abbreviations and symbols x

Chapter 1 Introduction 1

1.1 Introduction to FRIEND 1

1.2 Links with other international projects 4

1.3 FRIEND Report 4

References 5

Chapter 2 Northern Europe 7

2.1 Introduction 7

2.1.1 Regional characteristics and challenges 7

2.1.2 Northern European FRIEND project 8

2.2 The European Water Archive 9

2.3 Research 12

2.3.1 Low flows 12

2.3.2 Large-scale variations in hydrological characteristics 15 2.3.3 Techniques for extreme rainfall and flood runoff estimation 18 2.3.4 Catchment hydrological and biogeochemical processes in a

changing environment 21

2.4 Conclusions 24

2.4.1 Achievements 24

2.4.2 Future research developments 24

2.4.3 Policy and research 25

References 27

Chapter 3 Alpine and Mediterranean (AMHY) 29

3.1 Introduction 29

3.2 The AMHY database 30

3.3 Research 30

3.3.1 Regime modelling 32

3.3.2 Rare floods 34

3.3.3 Heavy rains 36

3.3.4 Erosion and sediment transport 38

3.4 Conclusions 38

References 39

Chapter 4 Southern Africa 41

4.1 Introduction 41

4.2 Data 43

4.3 Research 43

4.3.1 Flood frequency analysis 43

4.3.2 Analysis of rainfall drought 44

4.3.3 Identifying and monitoring river flow drought 46

4.3.4 Rainfall-runoff modelling 48

4.3.5 Other ongoing research 50

4.4 Training and capacity building 50

4.5 Conclusions 51

Acknowledgements 51

References 51

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Chapter 5 West and Central Africa (AOC) 53

5.1 Introduction 53

5.2 Data 54

5.3 Research 54

5.3.1 Water Resources Variability 54

5.3.2 Modelling of hydrological processes 55

5.3.3 Water quality 58

5.3.4 Low Flows 58

5.4 Training and capacity building 59

5.5 Conclusions 59

References 60

Chapter 6 Nile basin 61

6.1 Introduction 61

6.2 Data 62

6.3 Research 63

6.3.1 Rainfall-runoff modelling 63

6.3.2 Sediment transport and watershed management 63

6.3.3 Flood frequency analysis 63

6.3.4 Drought and low flow analysis 64

6.4 Training and capacity building 64

6.5 Conclusions 64

References 65

Chapter 7 Asian Pacific 67

7.1 Introduction 67

7.2 Asian Pacific Water Archive 68

7.3 Research 70

7.3.1 Water balance studies 70

7.3.2 Rainfall-runoff models 70

7.3.3 Statistical and stochastic models 73

7.3.4 Frequency analysis models 73

7.3.5 Human adjustment models 74

7.4 Training and capacity building 74

7.5 Conclusions 74

References 75

Chapter 8 Hindu Kush Himalayas 77

8.1 Introduction 77

8.2 Data 79

8.3 Research 80

8.3.1 Low flows 81

8.3.2 Floods 81

8.3.3 Rainfall-runoff 83

8.3.4 River water quality 83

8.3.5 Snow and glaciers 83

8.4 Training and capacity building 84

8.4.1 Review of training provided 84

8.4.2 Benefits from training 85

8.5 Conclusions 86

References 86

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Chapter 9 Mesoamerica and the Caribbean (AMIGO) 89

9.1 Introduction 89

9.2 Data 91

9.3 Research 92

9.3.1 Hydrological minima 92

9.3.2 Hydrological maxima 92

9.3.3 Ecohydrology 93

9.4 Conclusions 94

Chapter 10 Conclusions 95

10.1 Key achievements 1998-2001 95

10.2 FRIEND initiatives in IHP-VI 96

10.3 The future 98

References 98

Annex 1 Afrique de l’Ouest et Centrale (AOC) – en français 99

5.1 Introduction 99

5.2 Données 100

5.3 Recherche 100

5.3.1 Variabilité des ressources en eau 100

5.3.2 Modélisation des processus hydrologiques 102

5.3.3 Qualité de l’eau 104

5.3.4 Etiages 105

5.4 Formations et amélioration des moyens 105

5.5 Conclusions 106

Bibliographie 106

Annex 2 FRIEND coordinators 107

Annex 3 FRIEND research participants 108

Annex 4 FRIEND meetings 1997 – 2002 115

Annex 5 FRIEND publications 1997 – 2002 117

FRIEND 2002

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Acknowledgements

The main contributors to each chapter are listed below. The editors would also like to thank the many FRIEND colleagues who have contributed to this report through their research, by supplying information to the authors, preparing figures or translating text. The assistance given by our colleagues Maxine Zaidman, David Pitson and John Griffin at CEH Wallingford is also gratefully acknowledged.

Chapter 1 Introduction: G. A. Cole Contributors:A. Gustard, H.G. Rees.

Chapter 2 Northern European FRIEND: A. Gustard

Contributors: H.G. Rees, G.A. Cole (Section 2.2); L. Tallaksen, S. Demuth (Section 2.3);

L. Gottschalk (Section 2.4); S. Blazkova, T. Skaugen, K. Beven, A.L. Vetere Arellano, E.G. Langsholt, M. Astrup (Section 2.5); L. Holko, L. Andersson, J. Buchtele, F. Doležal, V. Eliáš, A. Herrmann, J. Hladný, Z. Kostka, A. Lepistö, P. Miklánek, G. Peschke, E. Querner, P. Seuna, M. Tesar, S. Uhlenbrook, P. Warmerdam, S. Zhuravin (Section 2.6).

Chapter 3 Alpine and Mediterranean FRIEND (AMHY): E. Servat Contributors:J.F. Boyer, V. Stanescu, P. Versace, M.C. Llasat, B. Touaïbia Chapter 4 Southern African FRIEND: S. Mkhandi

Contributors:D.A. Hughes, J.R. Meigh

Chapter 5 West and Central African (AOC) FRIEND: A. Amani

Contributors:A. Afouda, M. Maiga, G. Mahe, M. Nguetora, M.O. Ankomah, J.E. Paturel, L. Sigha, D. Sighoumnou.

Chapter 6 Nile FRIEND: M.S.M. Farid

Chapter 7 Asian Pacific FRIEND: K. Takeuchi Contributors:R.P. Ibbitt, Z. Xu

Chapter 8 Hindu Kush Himalayan (HKH) FRIEND: S. R. Chalise

Contributors:M.A. Kahlown, A.P. Pokhrel, S. I. Hasnain, B. P. Parida, K. B. Thapa, R. Rajbhandari, A. Shrestha, A.B. Shrestha

Chapter 9 Mesoamerican and Caribbean FRIEND (AMIGO): E. O. Planos-Gutierrez Contributors:F. Scatena, H. Thomas, C. Buján, B. Lapinel, R. Mejía, L. Montano

Chapter 10 Conclusions: A. Gustard

Annexes collated by G.A. Cole, based on information supplied by regional FRIEND groups.

The FRIEND Programme relies on the support of a large number of universities, government departments and research organisations, who have contributed data, staff or financial resources to the project. Support has also come from the European Union, the International Association of Hydrological Sciences (IAHS), WMO and national IHP Committees. The editors would particularly like to acknowledge the UK Department for International Development (DFID) for their support of FRIEND, including preparation of this report, and Mike Bonell and staff at the UNESCO Division of Water Sciences in Paris and at Regional UNESCO Offices, for valuable scientific and financial support to this publication.

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FRIEND 2002

Abbreviations and symbols

ADB Asian Development Bank

AGRHYMET Agricultural Hydrological Meteorological Training Centre, Niamey, Niger AHEC Alternative Hydro Energy Centre, Roorkee, India

AMHY Alpine and Mediterranean FRIEND AMIGO Mesoamerican and Caribbean FRIEND

AOC West and Central Africa (Afrique de l’Ouest et Centrale) FRIEND ARIDA Assessment of the Regional Impact of Drought in Africa

ARIDE Assessment of the Regional Impact of Droughts in Europe

ASTHyDA Analysis, Synthesis and Transfer of Knowledge and Tools on Hydrological Droughts

BALTEX Baltic Sea Experiment

BTOPMC Block-wise use of TOPMODEL coupled with Muskingum-Cunge method BUET Bangladesh University of Engineering and Technology

CATHALAC Water Centre for the Humid Tropics of Latin America and the Caribbean CEH Centre for Ecology and Hydrology (formerly Institute of Hydrology), UK Cemagref La Recherche pour l’Ingénierie de l’Agriculture et de l’Environnement CHASM Catchment Hydrology And Sustainable Management Project

CHMI Czech Hydrometeorological Institute

DANIDA Danish International Development Assistance

DEA Diplôme d’Etudes Approfondies (postgraduate diploma taken before a PhD) DEM Digital elevation model

DFID UK Government Department for International Development

DHM Department of Hydrology and Meteorology, HM Government of Nepal EEA European Environment Agency

EI, TU Engineering Institute, Tribhuvan University, Nepal

EIER Ecole Inter-Etats d’Equipement Rural (Interstate School for Rural Equipment) ENSO El Niño Southern Oscillation

ERB European Network of Experimental and Representative Basins ERICA EEA pan- European river network map

EU European Union

EUROSTAT Statistical Office of the European Communities EWA European Water Archive

FID 7-digit gauging station number on the European Water Archive FRIEND Flow Regimes from International Experimental and Network Data GAME Asian Monsoon Experiment of GEWEX

GCM General Circulation Model

GEWEX Global Energy and Water Cycle Experiment GIS Geographical Information Systems

GISCO EUROSTAT European Coastline map

GLUE Generalised Likelihood Uncertainty Estimation methodology

GRAPES Groundwater and River Resources Action Programme on a European Scale GRDC Global Runoff Data Centre, Koblenz, Germany

GTOPO30 USGS Digital Elevation Model

GWAVA Global Water Availability Assessment method GWP Global Water Partnership

HEAP Hydrological Extremes in Asian Pacific region HELP Hydrology for the Environment, Life and Policy

HKH Hindu Kush Himalayas

HKH FRIEND Hindu Kush Himalayan FRIEND

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HTC Regional Humid Tropics Hydrology and Water Resources Centre, Kuala Lumpur, Malaysia

HWRP Hydrology and Water Resources Programmes of WMO HYCOS Hydrological Cycle Observing System

HYDATA Hydrological database and analysis software, developed by CEH Wallingford IAHR International Association of Hydraulic Research

IAHS International Association of Hydrological Sciences ICID International Commission on Irrigation and Drainage

ICIMOD International Centre for Integrated Mountain Development, Nepal ICSI IAHS International Commission on Snow and Ice

IHD International Hydrological Decade IHP International Hydrological Programme

IIASA International Institute for Applied Systems Analysis IIT Indian Institute of Technology

IITF International Institute of Tropical Forests IMTA Mexican Institute of Water Technology

INTAS International Association for the promotion of cooperation with scientists from the New Independent States of the former Soviet Union

IRD Institut de Recherche pour le Développement, Montpellier, France IRTCES International Research and Training Centre on Erosion and Sediments ITCZ Inter-Tropical Convergence Zone

IWRA International Water Resources Association JNU Jawaharlal Nehru University, India

LOCAR Lowland Catchment Research Programme, UK.

NOAA National Oceanic and Atmospheric Administration, US Dept. of Commerce NRWQN National Rivers Water Quality Network, New Zealand

NVE Norwegian Water Resources and Energy Directorate OFDA Office of Foreign Disaster Assistance

OHP Operational Hydrological Programme

PARDYP The People and Resource Dynamics Project by ICIMOD PCRWR Pakistan Council of Research in Water Resources PDF Probability Density Function

RDBMS Regional Data Base Management System

REFRESHA Regional Flow Regimes Estimation for Small-scale Hydropower Assessment RHDC Regional Hydrological Data Centre

ROSTLAC Regional Office of Science and Technology of UNESCO for Latin America and the Caribbean

RSC Regional Steering Committee RWG Regional Working Group

SADC South African Development Community

SAGARMATHA Snow and Glacier Aspects of Water Resource Management in the Himalayas SAU Sindh Agriculture University

SGMRM Snow and Glacier Melt Runoff Model TAC Tracer Aided Catchment model

TAC Technical Advisory Committee of the Global Water Partnership

TECCONILE Technical Cooperation Commission for the Promotion of the Development and Environmental Protection of the Nile

TOPMODEL A rainfall–runoff model that bases its distributed predictions on an analysis of catchment topography

UNESCO United Nations Educational Scientific and Cultural Organisation UNEP United Nations Education Programme

UNITWIN United Nations Student Network USGS United States Geological Survey

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FRIEND 2002

WATAC West African component of Global Water Partnership WCRP WMO World Climate Programme

WECS Water and Energy Commission Secretariat WHYCOS World Hydrological Cycle Observing System WMO World Meteorological Organization

WR90 Water Resources 1990 study of South Africa and modelling system WRRI Water Resources Research Institute, Egypt.

WWAP World Water Assessment Programme YWRC Yangtze Water Resources Commission

Symbols

AMV Annual maximum series of drought deficit volumes ATD Annual total water deficit

B Runoff parameter in 4-layer tank model Cp Snyder’s peaking coefficient

CD Consolidated deposit area

CR Distribution coefficient in given period CS Coefficient of stability

DLTKR Depth of rainfall loss (inches)

Ei Eventi

EOF Empirical Orthogonal Function FA Frequency of occurrence H Entropy or stability index

Lcv L moment coefficient of variation

LP3/MOM Log Pearson Type 3 / Method of Moments

MAX Maximum flow

MIN Minimum flow

MF Mean flow

n Sample size

p Probability of occurrence of given hydrological event P Parent distribution

P3/ PWM Pearson Type 3 / Probability weighted moments PMP Probable Maximum Precipitation

Q Discharge (m3s–1)

Q90 Discharge (m3s–1) equalled or exceeded for 90% of the time Q95 Discharge (m3s–1) equalled or exceeded for 90% of the time

R Rainfall (mm)

r2 Correlation coefficient SDL Specific demand level

STRKR Loss rate function (inches per hour) T Return period (years)

Tp Basin lag time

TCEV Two parameter extreme value distribution WVL Waste and vacant land

Z Parameter representing runoff in 4-layer tank model

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Chapter 1 Introduction

1.1 Introduction to FRIEND

Water is an integral part of the environment, and is of vital importance to all socioeconomic sectors. Human and economic development is not possible without a safe, reliable water supply. With an increasing global population, the challenge of managing water resources grows. Conflicts between different water uses and users become more common, as increasing demands are placed on this limited resource. Misuse of water resources and poor water management practices have resulted in depleted supplies, falling water tables, shrinking inland lakes, and stream flows diminished to ecologically unsustainable levels. In addition, water pollution, originating mostly from human activity, is occurring even more frequently, decreasing the amount of water suitable for many uses. There are added risks and uncertainties associated with climate change, and the long-term impact on water availability is only now beginning to be understood.

Water stress, where the demand for freshwater water outstrips supply, is keenly felt all over the world. Europe, for example, has recently suffered a number of extensive and costly floods and droughts, problems of groundwater pollution, lake eutrophication, over abstraction of groundwater and degradation of wetlands. In parts of the Middle East, South Africa and Asia water shortages are stifling economic growth, limiting food production and depriving many of adequate clean water for drinking, cooking and personal hygiene. The effects are hardest felt by the most vulnerable in society, particularly women and children of the poorest families, who lack the adaptive capacity to cope with such water shortages. The challenge for the international hydrological research community is considerable: to develop better methods and tools to ensure more effective and sustainable management of an increasingly scarce resource and, through this, contribute to improving the quality of life for the poorest people in our global society.

FRIEND (Flow Regimes from International Experimental and Network Data) is one of the initiatives being undertaken by hydrologists to meet this challenge. FRIEND is a contribution to the International Hydrology Programme (IHP) of the United Nations’ Educational, Scientific and Cultural Organization (UNESCO), and aims to develop better understanding of hydrological variability and similarity across time and space, through mutual exchange of data, knowledge and techniques at a regional level. The project was founded in 1985 by a small international team of European scientists, who sought to realise operational benefits from the vast amount of information gathered from representative and experimental basins across northern Europe during the 1960s and 1970s. The outcome of their work attracted considerable attention and its merits ensured that FRIEND evolved through several successive phases to become the worldwide, regionally-based study outlined in this report. The growth of FRIEND has been significant, with some 100 countries now participating in the eight established regional FRIEND projects of Northern Europe (NE), the Alpine and Mediterranean region (AMHY), Southern Africa, the Nile Basin, West and Central Africa (AOC), the Hindu-Kush Himalayan region (HKH), the Asian-Pacific region and the Mesoamerican and Caribbean region (AMIGO) (Table 1.1; Figure 1.1). Meanwhile, interest in FRIEND continues to grow, with new projects being considered in central Asia, South America, and the Persian Gulf and Caspian Sea region.

FRIEND research covers a diverse range of topics including low flows, floods, variability of regimes, rainfall/runoff modelling, processes of streamflow generation, sediment transport, snow and glacier melt, climate-change and land-use impacts. As a result FRIEND has been elevated to the position of a crosscutting theme in the sixth phase of the IHP (IHP-VI) from 2002 to 2007, with links to such themes as global changes and water resources, integrated

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FRIEND 2002

Table 1.1 Countries participating in the FRIEND project

FRIEND Group Participating countries

Northern Europe Austria Belarus Belgium Czech Rep.

(24 countries, Denmark Estonia Finland France

established 1985) Germany Hungary Iceland Ireland

Latvia Lithuania Luxembourg Netherlands

Norway Poland Russia Slovakia

Sweden Switzerland Ukraine UK

AMHY Albania Algeria Bulgaria France

(17 countries, Greece Hungary Italy Lebanon

established 1991) Moldavia Portugal Romania Slovenia

Spain Switzerland Tunisia Turkey

former Yugoslavia

Southern Africa Angola Botswana Lesotho Malawi

(12 countries, Mauritius Mozambique Namibia South Africa

established 1991) Swaziland Tanzania Zambia Zimbabwe

Asian Pacific Australia Cambodia China Indonesia

(13 countries, Japan R. Korea Lao PDR. Malaysia

established 1997) New Zealand Philippines Thailand Vietnam

Papua New Guinea

West & Central Africa Bénin Burkina-Faso Cameroon C. African Rep.

(AOC) Chad Ghana Guinea Côte d’Ivoire

(16 countries, Liberia Mali Mauritania Niger

established 1992) Nigeria Sénégal Sierra Leone Togo

Hindu Kush-Himalayan Afghanistan Bangladesh Bhutan China

(8 countries, India Myanmar Nepal Pakistan

established 1996)

Nile Burundi D.R. of Congo Egypt Eritrea

(10 countries, Ethiopia Kenya Rwanda Sudan

established 1996) Tanzania Uganda

Mesoamerican and Anguilla Bahamas Barbados Antigua & Barbuda Caribbean (AMIGO) Belize Bermuda British Virgin Is Cayman Is

(31 countries & Costa Rica Cuba Dominica Dominican Rep.

administrative El Salvador Grenada Guatemala French West Indies

dependencies, Haiti Honduras Jamaica Neth. Antilles/Aruba

established 1999) Nicaragua Mexico Montserrat St Kitts and Nevis Panama Puerto Rico St Lucia Trinidad & Tobago Turks & Caicos Is US Virgin Is St Vincent & the Grenadines

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watershed and aquifer dynamics, land habitat hydrology, water and society and water education and training. The FRIEND programme also complements the other crosscutting initiative HELP (Hydrology for the Environment, Life and Policy), which aims to integrate hydrological science with social issues and provide the scientific basis for improved land and water management through a global network of experimental basins.

Activities within each regional FRIEND project are determined by local project participants, who are drawn from operational agencies, universities and research institutes, and are therefore in the best position to identify the research priorities in their region. The FRIEND project tends, therefore, to have a problem-solving approach in most of its regions, with its scientific output being applied practically towards hazard mitigation and poverty alleviation. As floods and droughts are not necessarily confined by political boundaries, the major efforts of regional FRIEND projects towards the sharing of data between countries and the establishment of regional hydrological databases, used for FRIEND research, have made a real and lasting step towards international cooperation. Such databases are now well established in the Northern European, AMHY, West and Central Africa (AOC) and Southern Africa FRIEND projects and are under development in the HKH, AMIGO and Asian Pacific FRIEND regions.

Several FRIEND projects, seeking to build the capacity of local hydrologists and water practitioners to assess and manage their own national water resources, have identified as a priority a need for training and skills transfer. Training and capacity building has become an important part of the FRIEND Programme and is conducted through training courses, technical workshops, conferences, symposia, the subsidised distribution of technical literature and support to postgraduate students. The transfer of skills, knowledge and experience between regional projects at different stages of development is one of the key achievements of FRIEND.

Figure 1.1 Location of FRIEND projects worldwide

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FRIEND 2002

1.2 Links with other international projects

The status of the FRIEND project within the international hydrological community is reflected in its many links to other international programmes and projects. The project has a particularly effective relationship with the World Meteorological Organisation (WMO), through elements of the Hydrology and Water Resources Programme (HRWP) and the World Climate Research Programme (WCRP). It was specifically praised for its close cooperation with WMO programmes at the Fifth UNESCO/WMO International Conference on Hydrology (UNESCO/WMO, 1999).

The Northern European FRIEND project has had a good relationship for many years with the Global Runoff Data Centre (GRDC), one of four sub-regional data centres of the FRIEND European Water Archive. There is also synergy between FRIEND and the WMO WHYCOS (World Hydrological Cycle Observing System) programme. Each of the three ongoing WHYCOS projects, in the Mediterranean basin (MED-HYCOS), southern Africa (SADC-HYCOS) and western and central Africa (AOC-HYCOS), coincides geographically with a regional FRIEND project and involves organisations that are also active within FRIEND. There are also collaborative links with WCRP’s GEWEX (Global Energy and Water Cycle Experiment) and at a regional level between Northern European FRIEND and BALTEX (Baltic Sea Experiment), Asian Pacific FRIEND and GAME (GEWEX Asian Monsoon Experiment), and AMHY and GEWEX-Rhône.

FRIEND works closely with the International Association of Hydrological Sciences (IAHS) in organising conferences and workshops and publishing conference proceedings. An example of this collaboration is the FRIEND 2002 conference in South Africa, the proceedings of which are published in the IAHS Red Book Series (van Lanen & Demuth, 2002). FRIEND participants are also working closely with the IAHS International Commission for Snow and Ice (ICSI) to establish a regional FRIEND project in South America, focusing on hydrological aspects of snow and ice in the Andes, and a training programme for glacier mass-balance monitoring in the Himalayas.

FRIEND has recently been developing links with the Global Water Partnership (GWP), which it joined formally in October 2000. The GWP is an independent global network that seeks to offer new and innovative ways of networking between stakeholders and to support countries in the sustainable management of their resources by bringing together research needs and donors. The GWP operates through a number of regional Technical Advisory Committees (TACs) and is working in many regions where FRIEND is already established. For instance, the research focus of the Southern Africa FRIEND project has been guided by the regional TAC, and many of the active FRIEND participants are also involved in the GWP.

In Europe, FRIEND has been supported by, and has contributed to, the Fourth and Fifth EU Framework Programmes for Research, Technological Development and Demonstration, with projects such as ARIDE (Assessment of the Regional Impact of Drought in Europe: see Section 2.3.1) and GRAPES (Groundwater and River Resources Action Programme on a European Scale). Cooperation between Northern European and AMHY FRIEND has provided major inputs to water resources analysis and synthesis by EUROSTAT and the European Environment Agency (EEA, 1998).

1.3 FRIEND Report

This volume is the fourth in a series of FRIEND Reports (Gustard et al., 1989; Gustard, 1993;

Oberlin & Desbos, 1997), which have been produced to mark the end of successive phases of FRIEND and to coincide with major international FRIEND Conferences held in Bolkesjø, Norway, in 1989, Braunschweig, Germany, in 1993 and Postøjna, Slovenia, in 1997 (Roald et al., 1989; Seuna et al., 1994; Gustard et al., 1997). This report presents research conducted

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during the fourth phase of FRIEND from 1998 to 2002 and coincides with the Fourth FRIEND Conference, Bridging the gap between research and practice, in Cape Town, South Africa, 18-22 March 2002.

The report presents a synthesis of global FRIEND research, giving the reader a flavour of the wide range of research activities addressed and the different problems faced by each regional FRIEND group. Following this introduction (Chapter 1), a chapter is devoted to each of the eight established regional FRIEND projects (Chapters 2 to 9). Each chapter was prepared by the regional FRIEND coordinator and project leaders, based on contributions from regional participants. They typically describe the hydrological challenges faced by the regional FRIEND group, its organisation and project development, an outline of the activities undertaken and selected examples of its research output. Chapter 10 provides a general conclusion, summarises the overall achievements of FRIEND and outlines future plans.

Chapter 5 on West and Central Africa /Afrique de l’Ouest et Centrale (AOC) was originally written in French and was translated into English at AGRHYMET, Niamey, Niger: the original French version is included as Annex 1. Annexes 2 to 5 give background information on the FRIEND project: contact details for the eight regional coordinators in Annex 2, FRIEND research participants in Annex 3, FRIEND meetings since 1997 in Annex 4, and about 450 publications by FRIEND participants since 1997 in Annex 5. Although it is impossible to provide a fully comprehensive picture of all regional groups, these annexes show clearly the vigour, high productivity and wide-ranging nature of FRIEND research and collaboration, and the wide dissemination of research results in scientific journals, conference proceedings, books and reports.

References

European Environment Agency. 1998. Europe’s Environment: The Second Assessment, Elsevier Science Ltd, ISBN 0080432042

Gustard, A., Roald, L.A., Demuth, S., Lumadjeng, H. & Gross, R. 1989. Flow Regimes from Experimental and Network Data (FREND). Institute of Hydrology, Wallingford, UK.

Gustard, A. (ed.) 1993. Flow Regimes from International Experimental and Network Data (FRIEND),Vol. I, Hydrological Studies; Vol. II, Hydrological Data; Vol. III Inventory of streamflow generation studies. Institute of Hydrology, Wallingford, UK.

Gustard, A., Blazkova, S., Brilly, M., Demuth, S., Dixon, J., van Lanen, H., Llasat, C., Mkhandi, S., & Servat, E.

(eds) 1997. FRIEND’97 – Regional Hydrology: Concepts and Models for Sustainable Water Resource Management. IAHS Publ. no. 246.

Oberlin, G. & Desbos, E. 1997. Flow Regimes from International Experimental and Network Data (FRIEND) Third Report: 1994-1997, Cemagref Éditions, France.

Roald, L., Nordseth, K. & Hassel, K.A. (eds) 1989. FRIENDS in Hydrology, Proc. Int. Conf., Bolkesjø, Norway.

IAHS Publ. no. 187.

Seuna, P., Gustard, A., Arnell, N.W. & Cole, G.A. (eds) 1994. FRIEND: Flow regimes from International Experimental and Network Data, Proc. Int. Conf., Braunschweig, Germany, IAHS Publ. no. 221.

UNESCO/WMO 1999. Fifth International Conference on Hydrology, Geneva, 8-12 February, 1999.

van Lanen, H.A.J. & Demuth, S. (eds) 2002. FRIEND 2002 – Regional Hydrology: Bridging the Gap between Research and Practice, Proc. Int. FRIEND Conf., Cape Town, South Africa, IAHS Publ. no. 274.

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Chapter 2 Northern Europe

2.1 Introduction

2.1.1 Regional characteristics and challenges

European inland waters are used for a variety of purposes, including drinking water, irrigation, wastewater disposal, power generation, transportation, fishing and other recreational activities.

Inland surface waters are also an important part of Europe’s landscape and the ecosystems that depend on them are of the utmost significance for biodiversity. Increasing population, industrialisation, the intensification of agriculture, canalisation, reservoir building and the growth in recreation have significantly increased the pressures on Europe’s inland waters, and there is increasing conflict between different uses and users. Droughts and floods, which are among the most common natural disasters, add to these problems. The need for sustainable management of water is evident.

Average annual runoff in Europe varies widely, from less than 25 mm in south-east Spain to more than 3000 mm on the west coast of Norway. Although arid or semi-arid regions are less prevalent in the Northern European FRIEND region, there are extensive areas with less than 150 mm of runoff, often coinciding with large population densities with high water demand.

Cooperation between the Northern European and the Alpine and Mediterranean (AMHY) FRIEND group has provided a regional analysis of European water resources for the European Environment Agency (EEA, 1998). For example, Figure 2.1 shows gridded average annual runoff across Europe at a 10 km grid resolution, based on both gauged and modelled data.

Even where there are sufficient long-term water resources, the seasonal or year-to-year variation in the availability of the resource may result in shortages. Figure 2.2 shows urban demand as a proportion of Q90 (the discharge exceeded or available for human and environmental demands for 90% of the time). This type of map is useful in identifying those regions of water stress, such as the urban areas and the Mediterranean coastline, which could be subject to seasonal water shortages.

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Figure 2.1 Map of average annual runoff in Europe

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Floods are the most common natural disaster and, in terms of economic damage, the most costly. In recent years, floods have received much media and public attention within Europe.

Some examples of serious floods are the Baison-la-Romaine flood of 1992, the Rhine and Meuse floods of 1993/94 and 1995, the Oder flood of 1997, the 1996 and 1997 floods in Biescas and Badajoz, the 1998 flood in Sarno and Quindici and the UK floods of 1998 and 2000/01. Flooding and its impact result from a combination of natural factors and human interference. Human actions can influence flooding either by affecting the runoff patterns (e.g. deforestation, urbanisation and river channelisation) or by increasing the possible impact of flooding (e.g. increased development of flood plains for housing).

Large areas of Europe have been affected by drought over the past 50 years. Recent severe and prolonged droughts have highlighted Europe’s vulnerability to this natural hazard and alerted the public, governments and operational agencies to the many problems of water shortage and the need for drought mitigation measures. As the pressure on existing water resources increases, the effects of a drought will be more keenly felt.

The provision of a common European database through FRIEND has enabled floods, low flow frequency and the dynamic characterisation of regional droughts to be studied for the first time at the pan-European scale. It has also allowed research into large-scale variations in hydrological characteristics and teleconnections and enabled results from studies of catchment hydrological and biogeochemical processes on small experimental catchments to be compared.

2.1.2 Northern European FRIEND project

The Northern European FRIEND project was started in 1985 by the IHP Committees of the UK, Germany, the Netherlands and Norway, who seconded full-time scientists for a three-year period to collaborate in an international project group based at the Centre for Ecology and Hydrology (formerly the Institute of Hydrology), Wallingford, UK. Hydrologists from other European countries soon joined them on secondment for shorter periods. The first phase of the project was completed in 1989 and led to the establishment of the European Water Archive, containing river flow data from 1350 gauging stations in 13 countries. The second, third and Figure 2.2 Map of urban demand as a proportion of Q90 (90th percentile flow)

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fourth phases of the Northern European FRIEND project, completed in 1993, 1997 and 2001 respectively, have seen participation extend to many countries in central and eastern Europe:

24 countries are now actively involved in Northern European FRIEND (Table 1.1). Close links are maintained with AMHY and considerable efforts are made by Northern European participants to support and develop the existing FRIEND projects in Southern Africa, the Caribbean and Hindu-Kush Himalayas, as well as emerging projects in Central Asia and South America.

As with other FRIEND groups, the Northern European project is overseen by a Steering Committee, with one representative from the IHP Committee of each participating country.

Administration is the responsibility of the project secretariat at CEH Wallingford, UK. Research is conducted by five project groups, each comprising ten or more participants representing different European countries. Project groups typically meet annually, providing a forum for participants to present their ongoing work and exchange ideas and knowledge. The five themes covered are low flows, floods, large-scale variations and teleconnections, catchment hydrological and biogeochemical processes, and hydrological database development. The activities of each theme are summarised in the following sections, starting with a description of the European Water Archive.

2.2 The European Water Archive

To develop a better understanding of the temporal and spatial variability of hydrological regimes requires good quality long-term flow and spatial data, that is representative of the study area. A central feature of Northern European FRIEND, since its inception in 1985, has been the development of a hydrological database, the European Water Archive. This archive is now arguably one of the most comprehensive hydrological archives in Europe, containing long-term daily flow data and catchment information for over 5000 river gauging stations (Rees & Demuth, 2000) in 30 countries. The continued development and maintenance of the archive is the responsibility of the Database group (Project Group 1), coordinated by the Centre for Ecology and Hydrology, Wallingford. This group has formal responsibilities, as specified by the Steering Committee of the Northern European FRIEND project, for coordinating data acquisition, applying quality control procedures and disseminating data to FRIEND researchers. Data is supplied to the archive on a voluntary basis and free of charge. In turn, the data is made freely available to FRIEND researchers on the condition it is used exclusively for FRIEND research.

The European Water Archive is located at the Centre for Ecology and Hydrology (CEH) Wallingford. It comprises two distinct elements: a relational database management system (RDBMS), based on ORACLE, which stores time-series of river flow data, catchment characteristics and pertinent derived flow statistics; and a geographical information system (GIS), which stores spatially referenced data as ARC/INFO coverages. For regional analysis both time series and spatial data elements are routinely used in conjunction with each other.

The European Water Archive currently contains the equivalent of over 140 000 station-years of gauged daily flow records from over 4600 catchments in 29 countries across Europe. The distribution of the stations is shown in Figure 2.3. The high density of stations in north-west Europe reflects the fact that FRIEND originated in this part of Europe with the data coverage only relatively recently being extended to central and eastern Europe and to the states of the former Soviet Union.

Every effort has been made to ensure that the data held on the Archive are of good quality.

Most data come from small, predominantly natural catchments, generally with a catchment area of less than 500 km2, where artificial influences on the flow record are no more than 10%

of the mean flow. Typically, stations have a complete daily flow record of at least ten years.

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Figure 2.3 Location of FRIEND gauging stations across Europe

Each station on the Archive is uniquely identified by a seven-digit FRIEND number (FID). The FRIEND station numbering is based on the subdivision of Europe into 44 hydrometric regions, with each region generally containing between 10 and 15 hydrometric areas of up to 10 000 km2. The general location of any gauging station can be inferred from the FID: the first two digits correspond to the hydrometric region, the next two to the hydrometric area, with the final three digits giving the sequential number of the station within the relevant hydrometric area.

As Table 2.1 shows, record lengths are generally long, averaging over 30 years per station, with a large number of stations with over 100 years of record. Gauged monthly flows are also available for a further 60 stations in Iceland, Poland, Luxembourg and Russia. In addition, 38 000 station years of instantaneous annual maxima (flood maxima) are available for over 2100 gauging stations in north and west Europe.

There has been a considerable expansion of the archive since the last FRIEND Report in 1997 (Oberlin & Desbos, 1997), when it contained 109 000 station years of gauged daily flow data from 4233 stations in 25 countries. The expansion was largely facilitated by two projects.

Firstly, the inclusion of data from three former Soviet Union countries was enabled by funding from INTAS, the International Association for the promotion of cooperation with scientists from the New Independent States of the former Soviet Union. The project resulted in a regional data centre of the EWA being established at the State Hydrological Institute in St Petersburg, Russia and the transfer over 9000 station years of gauged daily flow data, annual maxima and spatial data from 273 catchments in Russia, Belarus and Ukraine (Rees &

Cole, 1999). The second major source of data has been the European Union Fourth Framework

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Table 2.1 Summary of gauged daily flow data (GDF) on the FRIEND European Water Archive

Country Total no. of GDF % GDF Earliest Latest Station Record length (yrs) stations stns stns record record yrs (GDF) Av. Max.

Austria 139 139 100 1922 1996 4520 33 75

Belarus 40 33 83 1919 1995 1383 42 77

Belgium 110 75 68 1929 1997 837 11 54

Bulgaria 3 3 100 1978 1986 27 9 9

Czech Republic 34 27 79 1887 1993 1468 54 104

Denmark 43 35 81 1917 1997 2115 60 81

Finland 71 68 96 1847 1997 3674 54 144

France 1476 1333 90 1863 1992 29734 22 128

Germany 790 698 88 1884 1998 26600 38 113

Greece 2 2 100 1978 1980 6 3 3

Hungary 26 25 96 1935 1996 825 33 62

Iceland 8 8 100 1932 1994 386 48 61

Ireland 130 77 59 1940 1997 1908 25 57

Italy 252 252 100 1925 1990 3969 16 66

Netherlands 37 32 86 1901 1994 694 22 93

Norway 214 205 96 1871 1999 7894 39 127

Poland 61 29 48 1955 1992 738 25 36

Portugal 73 73 100 1920 1994 1092 15 71

Romania 35 33 94 1838 1990 1155 35 153

Russia 217 199 92 1928 1995 8674 44 63

Slovakia 23 23 100 1930 1992 1441 63 63

Slovenia 12 12 100 1945 1990 300 25 45

Spain 45 45 100 1942 1995 1582 35 54

Sweden 71 66 93 1907 1992 2583 39 85

Switzerland 132 75 57 1904 1992 2775 37 82

Turkey 12 12 100 1958 1991 201 17 33

UK 1116 1020 91 1879 2000 31939 31 121

Ukraine 69 58 84 1960 1990 1798 31 31

Yugoslavia 5 5 100 1978 1990 63 13 13

Summary 5248 4662 1847 1999 140381 30 153

funded ARIDE (Assessment of the Regional Impact of Droughts in Europe) project, which was completed in December 2000 (Demuth & Stahl, 2001). The project led to significant improvements in the spatial and temporal coverage of gauged daily flow data on the archive.

These included a 20% increase in the total number of stations having gauged daily flow data and, significantly, an increase of 50% in the number of gauging stations with over 30 years’

daily flow data.

To complement the time-series component of the European Water Archive, an ARC/INFO geographical information system (GIS) exists, comprising spatially referenced data (i.e. thematic and map-derived data) that are stored in digital form as ARC/INFO coverages. Coverages can be readily combined, compared and correlated with each other, thus providing a valuable tool for hydrological analysis. Facilities are available that make it possible to relate the coverages to the time-series described above. Some of the coverages held include:

l Topographic catchment boundaries for over 3000 catchments in northern Europe;

l The European Environment Agency’s 1:1 million pan-European river network, ERICA;

l The 1:1 million Soil Map of the European Communities;

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l Grids of EU land-use (forest, urban, lake) at 1.25 km × 1.25 km resolution;

l Grids of potential evaporation and actual evaporation for the whole of Europe at 0.5 km × 0.5 km resolution, as supplied by the IIASA;

l Grids of monthly precipitation, temperature, pressure and cloud cover at 0.5 km × 0.5 km resolution for the period 1901 – 1996, as supplied by the Climate Research Unit of the University of East Anglia;

l The USGS GTOPO30 digital terrain model;

l The Eurostat GISCO 1:1 million European coastline and national boundaries.

Unfortunately copyright restrictions prevent the distribution of several of the spatial data coverages to FRIEND participants. Nevertheless, most are readily available, either freely (at no cost) or for a nominal charge, directly from the supplier.

The European Water Archive is unquestionably a valuable resource and a prime example of what can be achieved by international cooperation. FRIEND participants all over Europe have expended considerable time and effort to make the European Water Archive the high quality dataset for regional hydrological analysis it is today. Many scientists have already benefited from its existence and have used the data to develop tools and methods that are used for water resources management and flood design. The Archive will become even more relevant as society demands greater understanding of the impacts of climate and land-use change on water resources and the incidence of hydrological extremes, such as floods and droughts.

2.3 Research

2.3.1 Low flows

Droughts are complex natural hazards that, to a varying degree, affect some part of Europe almost every year. The temporary shortage of water poses a great threat to nature, the quality of life and the economy. Any future increases in the demand for water will be most critical in periods of severe low flow and extensive droughts. As drought is a slowly developing phenomenon, only indirectly affecting human life, its impacts are often underestimated in relatively rich regions such as Europe. However, recent years have shown how vulnerable countries can be to drought, as they often cover larger regions and extend for longer periods than floods. Unlike aridity, drought is a naturally occurring phenomenon and can be character- ised as a deviation from normal conditions of such variables as precipitation, evaporation, soil moisture, groundwater or streamflow. The last two quantities, used to define a hydrological drought, represent the available water resources at a site or in a region, and their low flow and drought characteristics provide threshold values for different water based activities.

It is difficult, because of its complexity, to define precisely the onset, duration and severity of a drought. As a consequence there are numerous definitions available and a lack of consistent analysis tools. This has hampered the progress of research and limited operational applications, which favour standardised measures. Traditional low flow measures, defined as one characteristic of the low flow domain (e.g. the mean annual minimum flow), do not suffer the same constraints. Low flow processes and different low flow measures have been discussed thoroughly in earlier FRIEND reports. The focus in this phase of FRIEND has been on hydrological drought: its definition, extreme characteristics, variability in time and space and synoptic behaviour across Europe. Common to many of the studies is the use of the threshold level method to define drought events from a time series of observations. A sequence of drought events is obtained when the variable is below a threshold level, with each event being characterised in terms of its duration and deficit volume. The European Water Archive has offered a unique opportunity to study the regional behaviour of streamflow droughts.

Time series of precipitation, and groundwater recharge and heads have also been analysed.

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The work in the Low flow group has ranged from statistical multivariate analysis at the regional and European scale to physically-based and conceptual modelling studies at the catchment scale. A common objective has been to characterise the spatial and temporal variability of low flow and hydrological droughts and to identify the main factors governing low flow and droughts at different scales. As the Low flow group has continued to grow, cooperation has evolved around smaller groups, such as the European Union supported project ARIDE and the Eastern European group. This has proved an efficient way to organise the work, with common meetings or workshops every 12-18 months. More recently the Textbook group was established. Based on the vast experience of the members of the Low flow group, it was decided to produce a synthesis of this knowledge and publish a textbook on low flow and hydrological drought. The book is aimed at both professionals and students and will be published by Elsevier Science Publications in 2003. In addition to subgroup and common meetings, exchange of students and joint excursions have also proved to be beneficial.

The key objectives of the ARIDE project (1998-2000) were to improve the understanding of processes that control European droughts, our ability to predict their duration, magnitude and extent for a given frequency and the sensitivity of droughts to environmental changes (Demuth

& Stahl, 2001). Consistent drought definitions were derived and applied to quantify temporal and spatial variations in meteorological droughts in terms of lack of precipitation, as well as hydrological droughts in terms of streamflow and groundwater deficits (Hisdal & Tallaksen, 2000; van Lanen & Peters, 2000; Tate & Gustard, 2000). The main objectives of the Eastern European group (established in 1999) have been to exchange data, harmonise methods and software tools for drought analysis, and jointly synthesise the results. The focus has been on regional statistical methods, identification of important catchment and climate characteristics influencing severe droughts and long-term fluctuations in time series of drought. A regionalisation program for low flow and drought analysis has been developed and applied to a joint east-European dataset.

The research results of the low flow group have been published in international journals and conference proceedings and cover a wide range of low flow topics, e.g. the link between streamflow drought and atmospheric circulation patterns (Stahl & Demuth, 1999), impact assessment of drought mitigation measures (Querner & van Lanen, 2001), flow variables for ecological studies (Clausen & Biggs, 2000), assessment of small-scale hydropower potential (Rees, Croker, Prudhomme & Gustard, 2000), hydrological drought and climate variability (Kašpárek & Novický, 2002), frequency analysis of droughts (Tallaksen, 2000), seasonality aspects of low flows (Laaha, 2002), changes in water balance and hydrological drought in Poland (Kasprzyk & Pokojski, 1998), and changes in groundwater runoff in Slovakia (Fendekova, 1999). Two regional drought studies are presented in more detail below.

Have droughts in Europe become more severe or frequent?

As a part of the ARIDE project, a study was carried out to investigate whether droughts in Europe have become more severe or more frequent (Hisdal et al., 2001). The topic is important because many experts cite the occurrence of recent droughts as evidence of climate change.

More than 600 daily records from the EWA were analysed to detect spatial and temporal changes in drought patterns. Figure 2.4 shows the results obtained by applying the non- parametric Mann-Kendall trend test on annual maximum series of drought deficit volumes (AMV) for the period 1962-90. For most stations, there are no significant changes. However, distinct regional differences can be seen. Examples of increasing drought deficit volumes are found in Spain, the western part of Eastern Europe and in large parts of the UK, whereas, decreasing drought deficit volumes occur in large parts of Central Europe and in the eastern part of Eastern Europe.

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