TITLES IN TIIIS SERIES / DANS CETTE COLLECTION 1.
2.
6.
7.
8.
9.
1 0.
11.
*12.
Comi
The use of analog and digital computers in hydrology: Proceedings of the Tucson Sympo- sium, June 1966 / L’utilisation des calculatrices analogiques et des ordinatcurs en hydrologie : Actes du colloquc de Tucson, juin 1966. Vol. i & 2. Co-edi/iun IASH-Unescu / Coédition AIHS- Unesco.
Water in the unsaturated zone: Proceedings of the Wageningen Symposium, June 1967 / L’eau dans la zone non saturée : Actes du symposium de Wageningen, juin 1967. Edited by / Édité par P. E. Rijtema & H. Wassink. Vol. I & 2. Co-edition [ASH-Unesco / Coédition AIHS- Unesco.
Floods and their computation: Proceedings of the Leningrad Symposium, August 1967 / Les crues et leur évaluation : Actes du colloque de Leningrad, août 1967. Vol. 1 & 2.
Co-edition IASH- Unesco- W M O / Coédition A I H S - Unesco- O M M .
Representative and experimental basins: An international guide for research and practice.
Edited by C. Toebes and V. Ouryvaev. Published by Unesco. (Will also appear in Russian and Spanish.)
Les bassins représentatifs et expérimentaux : Guide international des pratiques en matière de recherche. Publié sous la direction de C. Toebes et V. Ouryvaev. Publié pur l’Unesco.
(A paraître également en espagnol et en russe.)
Discharge of selected rivers of the world / Débit de certains cours d’eau du monde**.
Published by Unesco / Publié par I’ Unesco.
Voi. I: General and regime characteristics of stations selected / Caractéristiques géné- rales et caractéristiques du régime des stations choisies.
Vol. II: Monthly and annual discharges recorded at various selected stations (from start of observations up to 1964) / Débits mensuels et annuels enregistrés en diverses stations sélectionnées (de l’origine des observations à l’année 1964).
*Vol. III: Mean monthly and extreme discharges (1965-1969) / Débits mensuels moyens et débits extrêmes (1965-1969).
List of International Hydrological Decade Stations of the world / Liste des stations de la Décennie hydrologique internationale existant dans le monde**. Published by Unesco / Publié pur l’Unesco.
Ground-water studies: An international guide for practice. Edited by R . Brown, J. Ineson, V. Konoplyantsev and V. Kovalevski. (Willalso appear in French, Russian and Spanish / Paraîtra également en espagnol, en français et en russe.)
Land subsidence: Proceedings of the Tokyo Symposium, September 1969 / Affttissement du sol : Actes du colloque de Tokyo, septembre 1969. Vol. I & 2. Co-edition / A S H - U n e s c o / Coédition A I H S - Unesco.
Hydrology of deltas: Proceedings of the Bucharest Symposium, M a y 1969 / Hydrologie des deltas : Actes du colloque de Bucarest, mai 1969. Voi. I & 2. Cu-edition ZASH-Unesco / Coédition A I H S - Unesco.
Status and trends of research in hydrology / Bilan et tendances de la recherche en hydrologie.
Publislied by Unesco
World water balance: Proceedings of the Reading Symposium, July 1970 / Bilan hydrique mondial : Actes du colloque de Reading, juillet 1970. Vol. 1-3. Co-edition ZASH-Unesco-
W M O / Coédition A I H S - U n e s c o - O M M .
Research on representative and experimental basins: Proceedings of the Wellington (New Zealand) Symposium, December 1970 / Recherches sur les bassins représentatifs et expéri- mentaux : Actes du colloque de Wellington (Nouvelle-Zélande), décembre 1970.
,union uolunie / Hors collection
Publié par I’ Unesco.
International legend for hydrogeological maps 1 Légende internationale des cartes hydro- géologiques**.
T o be published 1 A paraître.
** Quadrilingua1 publication: English-Freiich-Spanish-Russian.
Publication quadrilingue : anglais-lrançais-espagnol-russe.
World water balance
Proceedings of the Reading Symposium July 1970
Bilan hydrique mondial
Actes du colloque de Reading Juillet 1970
A contribution to the International Hydrological Decade U n e contribution à la Décennie hydrologique internationale
Volume 1
Con sumarios en español Pesm~e no PYCCKEI
IASH - Unesco - W M O
AIHS - Unesco - OMM
Gentbrugge-Paris-Genève 1972
Published jointly in 1972 by
thc 1nternational.Association of Scientific Hydrology (Sccretary: L. J. TISON), Braamstraat 61 (rue des Ronces), Gentbrugge (Belgium),
the World Meteorological Organization, 41 avenue Giuseppe Motta, Geneva, and Unesco, Place dc Fontenoy, 75 Paris-7’
Printed by Imprimerie Ceuterick, Louvain (Belgium) Publié en 1972 conjointement par
l’Association internationale d’hydrologie scientifique (secrétaire : L. J. TISON), Braamstraat 61 (rue des Ronces), Gentbrugge (Belgique),
l’organisation météorologique mondiale, 41, avenue Giuseppe-Motta, Genève, et l’Unesco, place de Fontenoy, 75 Paris-7’
Imprimerie Ceuterick, Louvain (Belgique)
The selection and presentation of material and the opinions expressed in this publication are the responsibility of the authors concerned and do not necessarily reflect the views of the publishers.
The designations employed and the presentation of the material do not imply the expression of any opinion whatsoever on the part of the publishers concerning the legal status of any country or territory, or of its authorities, or concerning the frontiers of any country of territory.
L e choix et la présentation du contenu de cet ouvrage et les opinions qui s’y expriment n’engagent que la responsabilité des auteurs et ne correspondent pas nécessairement aux vues des éditeurs.
Les dénominations employées et la présentation des divers éléments n’impliquent de la part des éditeurs aucune prise de position à l’égard du statut juridique de l’un quel- conque des pays et tzrritoires en cause, de son régime politique ou du tracé de ses fron- tières.
\..
(u
Unesco/lASH/WMO i972 Prinrid in BelgiumSC.7 I IXX.1 I IAF
Preface
The International Hydrological Decade (IHD) 1965-1967 was launched by the thirteenth session of the General Conference of Unesco to promote international co-operation in research and studies and the training of specialists and technicians in scientific hydrology.
Its purpose is to enable all countries to make a fuller assessment of their water resources and a more rational use of them as man’s demands for water constantly increase in face of developments in population, industry and agriculture. In 1970 National Coniinittees for the Decade had been formed in 105 of Unesco’s 125 Member States to carry out national activities and to contribute to regional and international activities within the programme of the Decade. The implementation of the programme is supervised by a Co-ordinating Council, composed of twenty-one Member States selected by the General Conference of Unesco, which studies proposals for developments of the programme, recommends projects of interest to all or a large number of countries, assists in the development of national and regional projects and co-ordinates international co-operation.
Promotion of collaboration in developing hydrological research techniques, diffusing hydrological data and planning hydrological installations is a major feature of the pro- gramme of the IHD which encompasses all aspects of hydrological studies and research.
Hydrological investigations are encouraged at the national, regional and international level to strengthen and to improve the use of natural resources from a local and a global perspective. The programme provides a means for countries weil advanced in hydrolog- ical research to exchange scientific views and for developing countries to benefit from this exchange of information in elaborating research projects and in implementing recent developments in the planning of hydrological installations.
As part of Unesco’s contribution to the achievement of the objectives of the IHD the General Conference authorized the Director-General to collect, exchange and disseminate information concerning research on scientific hydrology and to facilitate contacts between research workers in this field. To this end Unesco has initiated two collections of publica- tions: Stirdies and Reports in Hydrology and Technical Pupers in Hydrology.
The collection Stirdies and Reports in Hydrology is aimed at recording data collected and the main results of hydrological studies undertaken within the framework of the Decade as well as providing information on research techniques. Also included in the collection will be proceedings of symposia. Thus, the collection will comprise the compila- tion of data, discussion of hydrological research techniques and findings, and guidance material for future scientific investigations. It is hoped that the volumes will furnish material of both practical and theoretical interest to hydrologists and governments parti- cipating in the IHD and respond to the needs of technicians and scientists concerned with problems of water in all countries.
Unesco and the IASH have together undertaken the implementation of several impor- tant projects of the IHD of interest to both organizations, and in this spirit a number of joint Unesco-IASH publications are invisaged.
Similar co-operation is under way with WMO and several joint U n e s c o - W M O publi- cations are also planned.
Préface
La Décennie hydrologique internationale (DHI) 1965- 1975 a été ouverte par la Conférence générale de l’Unesco à sa treizième session pour favoriser la coopération internationale en matière de recherches et d’études et la formation de spécialistes et de techniciens de l’hydrologie scientifique. Son but est de permettre à tous les pays d’évaluer plus complè- tement leurs ressources en eau et de les exploiter plus rationnellement, les besoins en eau augmentant constamment par suite de l’expansion démographique, industrielle et agricole. E n 1970 des comités nationaux pour la Décennie ont été constitués dans 105 des 125 États membres de l’Unesco en vue de mener à bien les activités nationales et de participer aux activités régionales et internationales dans le cadre du programme de la Décennie. C e programme est exécuté sous la direction d’un Conseil de coordination composé de vingt et un États membres désignés par la Conférence générale de l’Unesco, qui étudie les propositions d’extension du programme, recommande l’adoption de projets intéressant tous les pays ou un grand nombre d’entre eux, aide à la mise sur pied de projets nationaux et régionaux et coordonne la coopération à l’échelon international.
Le programme de la DHI, qui porte sur tous les aspects des études et des recherches hydrologiques, vise essentiellement à developper la collaboration dans les domaines de la mise au point de techniques de recherches hydrologiques, de la diffusion des données hydrologiques et de l’organisation des installations hydrologiques. II encourage les en- quêtes nationales, régionales et internationales visant à accroître et à améliorer l’utilisation des ressources naturelles, dans une perspective locale et générale. I1 offre la possibilité aux pays avancés en matière de recherches hydrologiques d’échanger des idées, et aux pays en voie de développement de profiter de ces échanges d’informations pour I’élabo- ration de leurs projets de recherches et pour la planification de leurs installations hydrolo- giques selon les derniers progrès réalisés.
Pour permettre à l’Unesco de contribuer au succès de Ia D H I , la Conférence générale a autorisé le Directeur général à rassembler, échanger et diffuser les renseignements sur les recherches d’hydrologie scientifique et à faciliter les contacts entre chercheurs de ce domaine. A cette fin, l’Unesco publie deux nouvelles collections : (< Études et rapports d’hydrologie D et N Documents techniques d’hydIologie ».
L a collection N Études et rapports d’hydrologie n a pour but de présenter les données recueillies et les principaux résultats des études hydrologiques effectuées dans le cadre de la Décennie, et de fournir des renseignements sur les techniques de recherche. O n y trou- vera aussi les Actes de colloques. Cette collection comprendra donc des données, l’exposé de techniques de recherches hydrologiques et des résultats de ces recherches, et une documentation pour des travaux scientifiques futurs. On espère que des volumes fourni- ront aux hydrologues et aux gouvernements qui participent à la DHI des matériaux d’un intérêt tant pratique que théorique et qu’ils répondront aux besoins des techniciens et des hommes de science qui s’occupent, dans tous les pays, des problèmes de l’eau.
L’Unesco et I’AIHS ont entrepris de réaliser conjointement plusieurs projets inpor- tants de la DHI qui les intéressent l’une et l’autre; dans cette perspective, elles ont prévu un certain nombre de publications conjointes.
D e m ê m e l’Unesco et l’OMM coopèrent actuellement à des projets qui donneront lieu également à des publications conjointes.
Contents
Table des matières
Foreword-Avant-propos Introduction
World hydrology: status and prospects Principal problems of modern hydrology World water balance-A geophysical problem The water balance of the oceans
The scale of oceanic influence on continental precipitation Water balance-Indian Ocean
The hydrological cycle of Greenland and Antarctica Raymond L. Nace
A . A. Sokolov R. C. Sritcliffe M. 1. Budyko
P. S. Eagleson and R. F. Lariuière
K. R . Ratnanathan and P. R. Pishatory Svenn Oruig
x-XI XII-XIIII
Snow cover on the territory of the USSR as a water balance element Land glaciation part in the earth’s water balance
Les principaux problèmes d’évaluation des eaux souterraines et de ses mouvements à I’echelle continentale et à l’échelle mondiale
The role of underground flow in the water balance of the USSR Evaluation of the ground water balance of large territories
Importance de I’emmagasinement souterrain de l’eau dans l’établissement des bilans Évaluation des ressources de nappes peu profondes au moyen d’un indice de sensibilité Distinguishing winter from s u m m e r recharge to groundwater in southern Arizona by Surface waters as elements of the World Water Balance
A method for runoff-mapping from precipitation and air temperature data Forecasting of dry weather stream flow
Problems of evaluation of soil moisture for water balances on large areas Estimating the frequency distribution of hydrologic residence times
Experimental investigations and computation of evaporation írom water surface Cyclic variations of river discharge in the Northern Hemisphere
Continental precipitation and evaporation. A review of problems related to hydrological V. D. Komarou and E. G. Popou
V. M. Kotlyakou H. Schoeller
E. I. Kudelin, I. S. Zekiscr and O. V. Popou
A. A. Konoplyantseu Gilbert Castany
aux pluies deuterium analysis
R. Degullier et C. Joseph
E. S. Simpson, David B. Thorud and Irving Friedman
G.P. Kalinin and K. Szesztay H. Liebscher Adnan M. Alsaffar
Miroslav Kuiilek
T. G. Chapman V. 1. Kuznetsou
P. S. Kuzin cycle and water balance studies E. G. Popou
O n the questions of rainfall measurement and represcntativeness Estimation of precipitation as water balance element
John C. Rodda A. P. Bochkou
1 IO 19 24 34 39 41 49 54 51 65 71 78 84 I O0 102 115 122 129 136 153 160
165 173 186 Precipitation and evaporation: their practical and operational aspects for the water cycle
balance Jaromir N é m e c 193
Avant-propos
L e Conseil de coordination de la DHI a inscrit le problème du bilan hydrique mondial (inventaires, bilans, recherches et mesures) parmi les problèmes de recherches hydrolo- giques d’intérêt planétaire qui appellent une coopération internationale. L e Conseil a en conséquence recommandé que l’Unesco convoque un colloque sur le bilan hydrique mondial suivant les recommandations formulées par le groupe de travail du Conseil sur le bilan hydrique mondial.
C o m m e suite à cette recommandation, l’Unesco a convoqué le colloque à Reading, du 15 au 23 juillet 1970. L a Commission nationale du Royaume-Uni pour l’Unesco et l’organisation météorologique mondiale ont collaboré à l’organisation de ce colloque, qui a également reçu l’appui de l’Association internationale d’hydrologie scientifique.
U n comité d’organisation et le secrétariat ont assuré la préparation et le déroulement des travaux du colloque sous la direction du professeur R. C. Sutcliffe, de l’Université de Reading. Le colloque a réuni 242 participants venus de 39 pays des cinq continents, ainsi que les représentants de trois organisations internationales : l’Unesco, l’organisation météorologique mondiale et l’Association internationale d’hydrologie scientifique.
L e programme scientifique du colloque était axé sur les thèmes suivants, considérés à l’échelle planétaire :
Répartition : l’eau dans l’atmosphère, les eaux de surface (y compris les neiges et les Bilans et échanges : transports, flux et changements de phase.
Aspects géographiques : échelles de temps et d’espace d’importance planétaire.
Besoins en matière de recherche : précision et représentativité des observations, dévelop- pements théoriques, élaboration de modèles physiques et mathématiques des problèmes du bilan hydrique à grande échelle.
Soixante et onze communications en provenance de dix-neuf pays ont été présentées. Elles ont été examinées dans le cadre du programme esquissé ci-dessus et sont reproduites dans les présents Actes. Elles forment trois volumes, dont le troisième comprend, en outre, ia liste des participants et les comptes rendus des débats sur chaque communication.
Les communications sont publiées en français ou en anglais, avec des résumés analy- tiques dans les quatre langues officielles de l’Unesco (anglais, espagnol, français, russe).
glaces), les eaux souterraines.
Introduction
The British National Committee for the International Hydrological Decade was most gratified when Unesco agreed to hold the Symposium on World Water Balance in the United Kingdom and when the University of Reading was chosen as a suitable location, it was natural that I, as Professor of Meteorology in the university, should be asked to act as Chairman of the local Organizing Committee. The university claims no especial fame for its hydrology, but it has real interests in all three departments of the School of Earth Sciences, in geology, which offers a course in solid earth geophysics, in geography which has provided courses in hydrology for many years, and in geophysics, which includes both hydrology and oceanography in its bachelors’ and masters’ degrees. It is hoped that the university m a y recógnize our subject in a more specific and organized way in the years to come.
The subject of hydrology has tended to be linked closely with engineering, and rightly so, for it is an eminently useful science concerning one of our basic natural resources, as near to our human needs as the air w e breathe and the food w e eat. But on the occasion of this symposium, w e look at our subject mort from a fundamental scientific viewpoint.
W e look at the water naturally surrounding our planet, in the forms of ice and vapour as well as liquid water; w e consider h o w all the forms and distributions with their varying abundances are !inked together; w e consider especially h o w water as a natural resource becomes avdilabie over the different continents of the earth, and h o w it may be measured and conserved; w e examine the effect which m a n is having, wittingly or unwittingly, on this vital heritage; and we hope that our deliberations and discussions willshow h o w firm is the background of fact and theory upon which far-reaching decisions about our water supplies, always becoming more and more criticai, must be made in the years, decades and centuries to come.
if the International Hydrological Decade has done no more than force the countries of the world to look at their water on the world scale as a commodity they must inevit- ably share, and it has done much more than this, it will have justified the effort that has been made.
R. C. SUTCLIFFE Chairman, United Kingdom
Organizing Committee
Introduction
L e Comité national de Grande-Bretagne pour la Décennie hydrologique internationale fut très honoré quand l’Unesco accepta de tenir le colloque sur le Bilan hydrique mondial au Royaume-Uni et, quand L’Université de Reading fut choisie c o m m e siège de ce colloque, il était naturel que, c o m m e professeur de météorologie à cette université, il m e fût demandé de devenir le président du Comité local d’organisation. L’université ne se prévaut d’aucune renommée spéciale en hydrologie, mais elle marque un réel intérêt dans les trois départements de son École des sciences de la terre, en géologie qui présente un cours dans la géophysique des roches, en géographie qui a organisé des cours d’hydro- logie depuis plusieurs années et en géophysique qui comprend des cours tant en hydrologie qu’en océanqraphie pour ses grades de licencié et de maître. I1 est à espérer que I’univer- sité pourra reconnaître le sujet qui nous occupe d’une façon plus spécifique et pius organisée dans les années à venir.
L’hydrologie a une tendance à se lier intimement aux sciences de l’ingénieur et c’est logique car c’est une science éminemment utile pour ce qui concerne l’une de nos res- sources naturelles de base, aussi nécessaire à nos besoins humains que l’air que nous respirons et la nourriture que nous mangeons. Mais, k l’occasion de ce colloque, nous considérons notre sujet d’un point de vue plus fondamentalement scientifique. Nous prenons en considération l’eau entourant notre planète, que ce soit sous forme de glace et de vapeur tout aussi bien que sous forme d’eau liquide; nous considérons corninent toutes les forines et distributions avec leurs abondances variables sont reliées entre elles;
nous considérons spécialement comment l’eau, c o m m e ressource naturelle, est disponible sur les divers continents de la terre, et comment elle peut être mesurée et conservée;
nous examinons l’action que I’hoinme peut exercer sciemment ou inconsciemment sur cet héritage vital; et nous espérons que nos délibérations et discussions montreront la solidité de nos connaissances de fait et de théorie sur lesquelles on se basera pour prendre des décisions d’action à longue échéance au sujet de nos réserves en eau, devenant tou- jours de plus en plus critiques, dans les années, les décennies et les siècles à venir.
Si la Décennie hydrologique internationale n’a conduit les nations du monde qu’à étudier leurs réserves en eau à l’échelle mondiale c o m m e un article qu’elles doivent se partager (et la Décennie a fait beaucoup plus que cela) elle aura justifié l’effort qui a été fait.
R. C. SUTCLIFFE Président du Comité d’organisation du Royaume-Uni
World hydrology: status a n d prospecis
World hydrology: status and prospects’
R a y m o n d L. Nace U. S. Geological Survey Washington, D. C., USA
SUMMARY: The broad definition of hydrology used as a guide for the IHD programme is accepted.
Interpretation of the definition and of the role of hydrologists in modern problems, however, must be very liberal, because water cannot be studied realistically independently of other factors in the environment, including biological factors.
The ultimate aim of hydrological studies is to aid rational use of water for human purposes.
Aspects of hydrology which need further study and research are alinost limitless, and not all can be undertaken at once. Therefore, the likelihood of early payoff in practical problems willstrongly influence choice of priority among activities.
Basic data are essential both for water development and for research. Basic data for all hydrolo- gical and related parameters are deficient for huge areas of the world and many development projects are being designed and constructed without an adequate base of data.
‘I Deficient” and “adequate” are relative terms whose use commonly is subjective. Some deficiencies and inadequacies, such as those for streamflow, are less acute than is commonly supposed. Other data, such as those for dissolved and suspended solids in rivers, are inadequate by any standard for much of the world.
Modern methods of systems simulation, data reduction, analysis and extrapolation make apparent deficiencies in some kinds of data much less serious than they were a decade or two ago.
New methods for quickly obtaining synoptic and sequential.data for large areas also improve the prospects for world hydrology.
L’HYDROLOGIE MONDIALE, SA SITUATION ET SES PERSPECTIVES
RESUME : O n accepte la définition répandue de l’hydrologie qui a guidé le programme de la DHM.
Cependant l’interprétation de la définition et du rôle des hydrologues dans les problèmes modernes doit être très large car l’on ne peut étudier l’eau avec réalisme indépendemment des autres facteurs du milieu, les facteurs biologiques y compris.
Le but définitif des études hydrologiques est de tendre vers un usage rationnel de l’eau pour les besoins humains. Les aspects de l’hydrologie qui ont besoin des études et des recherches additio- nelles sont presque sans limite, mais l’on ne peut pas tout entreprendre en mëme temps. Donc la probabilité d’obtention des résultats définitifs applicables aux problèmes pratiques influera fortement la priorité des activités.
LeScdonnées de base sont essentielles à la fois pour l’exploitation des ressources en eau et pour la recherche. Les données de base sur tous les paramètres hydrologiques et sur tous les paramètres associés sont déficientes pour des territoires immenses du monde, et de nombreux projets de développement sont projetés et réalisés sans données suffisantes.
((Déficient >) et G suffisant >) sont des mots relatifs dont l’usage courant est subjectif. Quelques déficiences et insuffisances, telles que celles sur l’écoulement des eaux de surface, sont moins prononcées que l’on présume à l’ordinaire. D’autres données, telles que celles sur les solides dissous et en suspension dans les rivières, sont insuffisantes par n’importe quelle norme.
A
cause de l’efficacité des méthodes modernes pour la simulation des systèmes et pour la réduction, l’analyse et l’extrapolation des données, les insuffisances apparentes sont beacoup moins graves qu’elles ne l’étaient voici une ou deux décennies. Les nouvelles méthodes d’obtention rapide des données synoptiques et successives sur des grands territoires améliorent égaiement les perspectives de l’hydrologie mondiale.1. Publication authorized by the Director, U.S. Geological Survey
Raymond L. Nace
HIDROLOGIA MUNDIAL: SITUACION Y PERSPECTIVAS
RESUMEN: Se acepta la amplia definición de hidïología utilizada como guia para ei programa del DHI. N o obstante, la interpretación que se da a esa definici6n y el papel que desempeñan los hidrólogos en los problemas actuales deben ser muy generosas ya que, en realidad, los recursos hidrológicos no pueden estudiarse independientemente de otros factores, tales como el medio ambiente, e incluso los factores biológicos.
EI fin que se persigne con los estudios hidrológicos es racionalizar de forma mas completa la utilización del agua destinada a los fines humanos. Los aspectos de la hidrologia que requieren un estudio amplio más y una investigación mas detallada son casi ilimitados y no todos pueden emprenderse inmediatamente. Por lo tanto, es más que probable que al tener que decidir cuáles son las actividades más urgentes, la selección se haga en función de la rentabilidad de los proyectos escogidos.
Tanto para fomentar los recursos hidrológicos como para la investigación de los mismos, es esencial disponer de una información básica. Existen inmensas zonas del mundo para ias cuales existe una carencior da datos básicos en lo que respecta a los recursos hidrológicos y a los correspondientes parámetros y muchos son los proyectos en desarrollo que se conciben y llevan a cabo sin una información adecuada.
«Carencia» y «adecuada» son términos que se utilizan a menudo en el sentido subjetivos Ciertas carencias y faltas de adaptación, tales como las que se refieren al flujo, son menos grave de lo que, por lo general, se supone. Otros datos, tales como los relativos a las materias disueltas y en suspensión en los rfos resultan inadecuados desde el punto de vista normative en mucha.
partes del globo.
Los métodos modernos que consisten en sistemas de simulación, de redución de datos, de análisis y extrapolación de los mismos ponen de manifesito que existe una carencia de cierto tipo de información, aun cuando de forma menos acusada que hace 10 Ó 20 años. Los nuevos métodos que permiten obtener rápidamente datos sinópticos y secuenciales para zonas importantes también permiten mejorar las perspectivas de la hidrologia mundial.
World hydrology: status and prospects
I N T R O D U C T I O N
Not quite 300 years have elapsed since Pierre Perrault, E d m é Mariotte and E d m o n d Halle set hydrology on its modern scientific path. During this period hydrologists have concen- trated chiefly on phenomena at the relatively small and intermediate scales-the local area and the river basin. Only recently has much attention been given to the extremes of scales-the microscopic and the global.
M a n y problems require research at the micro-scale. Examples are the specifics of water movement through aquifers, soils and vegetation, directional variation in aquifer permeability, and osmotic processes in semi-permeable geologic materials. But many problems already on the horizon require research at the macro-scale, involving whole continents, the great icecaps, the ocean and the entire world. In accord with the title of this symposium, this paper deals only with macro-scale phenomena.
Whether large-scale water-balance studies and inventories have any great practical value has been questioned often. They are, in fact, important for several practical reasons quite beyond their scientific interest. The impact of human activity on the environment is widely recognized but poorly documented, especially at large scale. Future impact will be much greater because burgeoning population willrequire manipulations of the environ- ment on an ever-growing scale. Transbasin diversions of water, for example, are not yet common, but already transcontinental diversions have been discussed. Without accurate knowledge of present large-scale water balances, it willbe impossible to predict the environ- mental effects of future large scale manipulations of the environment, including.land and water use, rain-making and other activities. All of these have international hydrological meteorological, sociological, economic, and legal implications. N o nation, however, small, can afford to ignore large-scale phenomena.
TOTAL WATER
The vast basin of the world ocean contains somewhat more than 97 percent of all free water in existence. Refinement of knowledge about the topography of the ocean floor will neither change water-volume estimates appreciably nor significantly affect studies of water balances. Likewise, refinements of estimates of water in other realms, although they are important in themselves, would not noticeably affect the estimated total volume of all water, because the amounts in those realms are very small percentages of the total.
Modern calculations of the total amount of water in the atmosphere, seasonally and on the average, differ by only a few tens or hundreds of cubic kilometers. Refinement of these calculations for long-term inventory purposes does not seem to be worth much effort, because the results would add nothing to the concept of static water balances. For the study of dynamic balances, however, vapour fluxes and regional and seasonal changes in atmospheric storage have great importance. Several papers in this symposium willdeal with these phenomena.
Only very crude estimates are available of water in readily accesssible realms, such as channel storage in rivers and impoundments in lakes. Channel storage is insignificant as a percentage either of total water or of transient water in the land areas at any given time.
Nevertheless, channel storage is important in flow routing and reservoir operation, and for many other purposes, yet it has received surprisingly little attention.
Rovrnond L. Nuce
Lake-water resources in general are poorly known. The Great Lakes system of North America has been inventoried with sufficient accuracy that only minor refinements may be expected in the future. However, only rudimentary hydrometry is available for many large lakes in North America, for the huge lakes of Africa, and for some of those in Asia.
The hundreds of thousands of smaller lakes in all continents have not been carefully inven toried. These are highly significant in regional water inventories, and they, in conjunction with wetlands and waterlogged areas present vast areas for evaporation.
For example, about 192 O00 km2 of the United States is inland water area. This is far more area than that of any single lake in the world except the Caspian Sea. Inland water areas of the world probably exceed 1 million km'.
Water in the icecaps of Antarctica, Greenland, and dozens of lesser icecaps generally is considered to be peripheral to the interests of hydrologists. However, if water inventories have any value, their value is incomplete without an account of snow and ice. Furlher, the great icecaps, ice shelves and sea ice have major roles in heat balances and hence in vapour balances and fluxes.
The volume of water in perennial snow fields and glaciers is another virtually unknown quantity, despite the importance of snow and ice as nonstructural storage reservoirs.
Although snow and ice are receiving considerable attention in Europe, Soviet Asia, and North America, two important areas have received little attention and have no prospect of early regional study. These are the great snow and ice fields of the Himalaya and Andes Mountains.
Despite studies of soil moisture and ground water during many years in all parts of the world, virtually no data are available on the absolute quantity of subterranean water.
Estimates have been made for a few isolated areas, but only the crudest of estimates are available for the land areas as a whole. Whatever their amounts may be, they m a y be considered as constants for long-term averages in large areas. But for short periods or small areas they are variables and must be accounted for in dynamic terms,
VAPOUR A N D WATER FLUXES
Storage and residence times of water in various realms are important for water inven- tories, but they imply a steady-state balance, whereas the hydrological cycle is a system of processes which both upset and tend to restore balances. Fluxes, changes of state, and changes in storage have importance in the study of water balances.
Vertically integrated horizontal vapour fluxes need much more attention. Aerological observations of vapour-flux divergences permit indirect determination of evaporation and precipitation, and the method is especially useful for large areas. Existing observation networks should be greatly extended and their density increased. This method, although not new, is in its infancy. So far it has depended on airborne, and rocketborne sensors which, unfortunately, sample only slender columns of the atmosphere. Orbiting sensors probably will provide essential supplemental or primary data in the future, and this technique should be fully exploited.
EVAPORATION
Evaporation data are very deficient for large areas of the world, especially for the vast areas of the world ocean. Calculated values for world evaporation, based on theory, require extensive extrapolations and interpolations from sparse observational data.
The poor state of knowledge about evaporation is well known and need not be belaboured here. The world water balance study requires more basic data for bare and vegetated land,
World hydrology: statiis and pro.fpects
wetlands of all kinds, for free water surfaces of ponds, lakes, inland seas and the world ocean, and for areas of snow and ice.
PRECIPITATION
Most precipitation, like most evaporation, occurs in oceanic areas, and no prospect is in sight for accurate direct measurement in that vast area. In land areas the problem is less formidable but, even so, no economically feasible density of stations could give a precise measure of precipitation. For all but small local areas special studies, therefore, estimates of gross precipitation will continue to be made. These approximations must be
improved by refinement of theory and by improved technology and observation.
RUNOFF
I will deal with runolï in some detail because for this factor we have sufficient data to make a crude evaluation of the state of knowledge. It is commonly believed that runoff from land areas to the world ocean is quantitatively known with sufficient accuracy for most broad-scale hydrological studies. Classifical studies treat all continental water yield as runoff. This may be unimportant if ground-water discharge is insignificant.
Data on ground-waler discharge (which I shall call runout) are so deficient that no valid estimate of its magnitude is possible. However, some simple estimates and calculations point to its probable magnitude.
In coastal areas in general, one of the following conditions prevails: (a) dense rock having very low permeability; (h) permeable rock or sediments in which, however, the hydraulic gradients are low and the runout cross-section is thin. Runout per kilometer of shoreline probably is small except in special areas such as Hawaii, Florida, some Mediterranean countrics, and a few other areas.
The toral shoreline length of world areas is about 370 O00 krn. Permanently frozen land areas such as Antarctica, Greenland and Arctic lands probably have no significant runout. Suppose. however, that runout occurs along 200 O00 k m of shoreline and that it is at the rate of 35 Is- based on assumption of25 percent porosity of the aquifer, vertical discharge zone 4 m thick, and an underflow rate of 3 m d - l. The average total runout then would be about 7 O00 rn3 s-'. This is less than I percent of estimated surface runoff. While the calcultion is wholly hypothetical, it is based on liberal assump- tions. In order to be significantly large the value would have to be greater by a factor of 5. Evidently, runout is negligible in relation to the world water balance, though it is significant within some regions.
A more significant matter is that classifical estimates of total runoff do not seem to be verified by analysis of data for rivers whose discharge is known within reasonable limits.
Such an analysis discloses some interesting facts, using data for rivers that discharge to the sea.
Table 1 and figure I show the estimated discharges of several hundred rivers, grouped by orders of magnitude of discharge (see footnote to table 1). It is believed that the data include all rivers of Orders I and TI and most rivers of Order IIT, but they include only a non-systematic sampling of lesser rivers that discharge to the sea. The data include 68 great rivers (those whose average discharge is 1 O00 m3 s-' or more).
The single first-order river discharges an average of 175 O00 m3 s-' from a drainage area of 6.3 x IO6 km2. The 15 second order-streams discharge at an aggregate average rate of 285 700 m3 s-
'
from an area of 27.5 x IO6 k m 2 . The 52 third-order rivers discharge about 148 O00 m 3 s-'
from an area of about 19.6 x IO6 km2. The aggregate averagek m ~
Raymond L. Nace
TABLE 1. Estimated discharge to the sea of principal rivers of the world and a sample of smaller rivers
Average annual discharge R a n k (a)
(order)
N u m b e r of rivers Drainage area (km2 x 10-3)
I II III IV V Totals
1 6 300 175 O00 27.8
15 27 485 285 130 10.4
52 19 558 148 286 1.58
133 7 205 49 030 6.80
103 1382 3 914 2.83
304 61 930 661 960
- __ __
~Average unit-area yield 10.7
(a) Ranked by orders of magnitude of discharge as follows:
i. 2 100 000 m3 s-1 11.2 10000but < 100OOO III.> 1 O00 but < IOOOO IV. 2 100 but < 1 o00 V . 2 10but < 100
(b) Here and at s o m e places in the text, the values shown are for bookkeeping purposes. They do not imply accuracy within 1 m3 s-l.
YI c?
E
2oc)
t
œ 4
I 'O0
t
U I : '
rn
O
1
v) œ
Lu 1
N -Y E
Q
2
I I I I I I IV V
S T R E A M O R D E R
FIGURE 1. Comparison of aggregate discharges and drainage areas of rivers, by order of magnitude
discharge of all 68 rivers is 609 O00 m3 s-' from an area of about 53.4 x IO6 km2. A non-systematic sample of 133 fourth-order rivers of the world (100 to 999 m 3 s-') has an aggregate discharge of about 49 O00 rn3 s-' from an area of about 7.2 x IO6 km2.
A similar sample of 103 fifth-order rivers discharges about 3 900 m 3 s-' from an area of about i .4 x IO6 km2.
World hydrology: status and prospects
A s a basic for the graphic presentation in figure 2, river-discharge data were tabulated with the rivers ranked numerically in decreasing order of magnitude of average discharge.
Using numerical rank, discharge of the Amazon River was plotted as number 1. The discharge of the Amazon plus that of the Congo is number 2. The Amazon plus the Congo plus the Yangtze is number 3, and so on to number 68, which represents all the great rivers of the world. Beyond number 68 the additional increment at number 100 includes 32 streams of Order IV. Points beyond that represent increments for groups of 50 to a total of 300 rivers.
700 I I ( I I I I I I I
,
I I lib
x 600--
E
z
500-u;
- -
o
- -
U
I I 1 1 1 1 1 1 I I I I 1 1 1 I I >
2 5 IO 20 50 100 200 400
lool
SERIAL NUMBER OF RIVERS
I I 1 1 1 1 1 1 I I I I 1 1 1 I l
2 5 IO 20 50 100 200 400
lool
SERIAL NUMBER OF RIVERS
FIGURE 2. Semi-logarithmic graph of discharge of 300 rivers of the world
The smoothness of the sinusoidal curve has no special significance. It is built in by the method of plotting. The significance of the curve is that it seems to be approaching a limitbelouw the value of 700 o00 m 3 s-'.
Based on some classificai studies, modified by unpublished data, the estimated aggregate oceanic discharge of all rivers of the world is about 924 O00 m 3 s-'. Large areas of some continents, chiefly deserts and endorheic basins, contribute no runoff to the sea. Exclud- ing these and icecap areas, the actual runoff-contributing area is about 103 x
lo6
km'.The aggregate discharge of the 68 principal rivers of the world is about 608 O00 m 3 s - l
from 53.3 x IO6 km'. These are 66 percent of estimated total discharge and 52 percent of the contributing area.
Great rivers are great because their basins have high unit-area yields, are very large, or both. Excluding the Nile, whose unit yield is low because of the large desert part of its basin, the unit-area yields of great rivers (Orders I to III) range from 2.7 to 32 Is-' km2 and they average about 12 1s- km'.
M a n y lesser rivers have high unit yields (up to 40 I~-lkm-~), but their basins are small and they add little to total discharge. The average yield of the sample of 133 IVth- Order rivers is 6.8 Is-'km-'.
In summary, the 300 rivers treated in the accompanying graphs and table drain about 63 percent of the world's runoff-contributing area and yield about 72 percent of estimated
Raymond L. Nace
total world runoff. Is it reasonable to expect that the remaining contributing area of 38.1 i( IO6 k m 2 produces the additional yield of 260 435 m3s-’? The fact that the right limb of the line in figure 1 is approaching a limitdoes not necessarily mean that the answer is “no”. The facts and estimates presented thus far raise several possibilities:
(i) aggregate oceanic discharge of all rivers is considerably less than has been estimated;
(2) the total discharge of the larger rivers is considerably underestimated; or (3) some large areas of high yield are not represented.
Possibility (i) may be tested by use of data for European rivers. Forty-one- large European rivers for which records have been assembled have an aggregate drainage area of 4 850 850 km’. Their aggregate average discharge is 36 O00 m 3 s-
’,
and their average unit-area yield is 7.42 Is-’ km2. The total European area that contributes runoff to the sea (excluding Iceland and the endorheic Caspian basin) is about 7 857 000 km’. The residual area not represented by the 41 rivers is 3 006 150 km’. If ttie water yield of this area is equal to the average for the 41 rivers, then the additional yield is 22 500 m3 s-’and the total for Europe as a whole is 58 500 m3 s-’. This is considerably less than 75 O00 m3 s- which is one widely used estimate for European water yield. The deficiency is 16 500 m3 SC’, or 22 percent of the larger value. It seems possible that European water yield has been overestimated.
Concerning possibility (2), that the total discharge of individual large rivers has been underestimated, it willbe recalled that the Amazon, when systematically measured in 1963-1964, was found to have a discharge nearly twice as large as was previously estimated It now ranks nearly 4% times the discharge of the Congo, but the latter also may be considerably underestimated. Moreover for certain large rivers such as the Brahmaputra, Ganges, and Orinoco data are poor, especially for high and flood discharges. However,
it w e double the discharge of the Congo and increase the discharge of all other Second- Order rivers by 10 percent, w e add only 70 O00 m3 s-’ to the total and the curve in figure 2 seems to approach a limitof about 734 O00 m3 s-’. It seems unlikely that under- estimation of individual river discharges is great enough to account for the discrepancy.
Concerning possibility (3), it is a fact that some areas of high yield are not represented in the data used. No data have been obtained for individual rivers of Taiwan, for instance, but the total discharge from its 35 700 km2 of area reportedly is 1 744 m3s-’, or 49 1 s-
’
km2. Malaysia and Indonesia, with an aggregate land area of 2 183 O00 k m 2 are high yield areas (ignoring the fact that the eastern part of Indonesia is comparatively dry). If their yield is comparable to that of Taiwan, they may add about 107 O00 m3 s-’to the world total. This would raise the right limb of the line in figure 2 to about 770 O00 m 3 s-’, but the line would still seem to be nearing a limitbelow the classical estimate of 924 O00 m3 s
-
I.The number of rivers, by itself, may have no significance as used in the foregoing discussion. The.compilation, however, does include all or nearly all large rivers. If the compilation were carried out to the n-th order of measurable streams, their number would be very large, but the area drained is limited, not infinite. The question remains therefore, whether this would significantly change the apparent total discharge indicated by figure 2.
A plot on logarithmic paper of the data for stream Orders I-IV, using cumulative dis- charge on one ordinate and cumulative area on the other, yields a straight line and, if this is projected to the full contributing area it indicates a yield of 880 O00 m3 s- ’. This is about 5 percent below the classical estimate. O n the other hand, it seems to m e that the data for fifth-order rivers cannot be ignored. In contrast to an earlier statement about large rivers, small streams are small because their basins are small, or their unit yields are small, or both. It seems unlikely that a sample of 100 rivers of Order V from many parts of the world be so atypical or biased on the low-yield direction that they must be regarded as extraordinary and the data ignored. For example, some small streams have unit discharge as high as 100 Is-’, but their drainage areas are on the order of a few hundred
World hydrology: status a n d prospects
square miles. Others with yields of a small fraction of a liter per second have drainage areas of several hundred thousand square kilometers. The latter type of streams causes the very low over-all average yield.
SUMMARY AND CONCLUSIONS
The most important of all parameters from the standpoint of global water balance is the sea-air interface. Meteorological data for most oceanic areas are sufficient to give only a crude picture of conditions on any given day. Gaps in data willshrink with the esta- blishment of more and better drifting and fixed weather buoys and use of communications satellites, if plans for the World Weather Watch come to fruition. The oceanographic counterpart, the Integrated Global Ocean Station System of the Intergovernmental Oceanographic Commission also will add to the store of information. These are vital to world hydrology and should be encouraged by the hydrological community.
Remote-sensing experiments with instruments in the Nimbus 3 satellite (launched 14 April 1969) indicate that it is possible to sense the vertical distribution in the atmosphere of temperature and water vapour. It may also be possible to measure ocean-surface temperatures. The promise from studies of hemispheric and global atmospheric vapour Auxes should be exploited fully, as this is one of the very few possibilities for determining regional evaporation and precipitation.
Soil moisture and ground water are two of the most difficult parameters to evaluate.
Were they not difficult the task would have been accomplished long ago.
Global water budgets may be made to balance nicely on paper on the basis of theory and by adjustment of the several components to force a balance. Estimates of individual parameters, however, when independently derived from real data, do not fit these balances.
The fact that it is necessary to juggle data, for example, those for streamflow, in an effort to reach agreement with classical estimates is symptomatic of the unsatisfactory state of knowledge. If this is true of streamflow, one of the most readily measurable parameters, how much more true must it be of other parameters of the hydrological cycle!
Nearly all large rivers of the world probably need restudy, including measurement at the head of tidewater and estimates by standard methods of ungaged increments of runoff and runout into tidal reaches below gaging stations. Flood discharge of most rivers needs increased attention. Meantime, more complete compilatioqs should be made of existing data. These data should receive more careful and sophisticated analysis than the simple treatment in the present paper.
It is evident that new or improved measurements of small rivers would not have much effect on estimated total discharge of all rivers to the sea. The total amount of water discharged b.y. these .rivers would .be less than the probable error in measurements of large rivers. For example, the error in estimated flow of the Amazon probably is about 10 percent or about $17 500 m 3 s-'. Only nine rivers in the world discharge more than that amount.
O n the other hand, lesser rivers have great practical importance in local and regional economies. Relatively speaking, major rivers such as the Amazon and Congo are scarcely used at all except for navigation. O n the other hand, a minor river such as the Colorado of the United States is completely used and it is the figurative lifeblood of an area of hundreds of thousands of square kilometers. In much of the world, therefore, hydrological study of rivers has great potential value for human interests and for study of local or regional water balances.
Studies of hydrology in its large-scale and ecological coritexts are essential. M a n has already affected and, in many ways, unfavourably affected the world environment.
With human activity increasing on an exponential scale, it is imperative that extensive
A. A. Sokolou
and intensive studies be made, lest further activity causes incalculable damage to the environment.
ACKNOWLEDGEMENTS
I wish to acknowledge with sincere thanks, many helpful suggestions and constructive criticisms from m y colleagues M . A . Benson, S.M. Lang, Allen Sinnott, T.E.A. Van Hylckama, and Alfonso Wilson.
Principal problems of modern hydrology
A. A . Sokolov,
State Hydrological Institute, Leningrad, USSR
SUMMARY: The water balance of reservoirs, the interrelation of surface and ground water, the water and salt balance of irrigated land, the water balance of swamp areas and the influence of m a n on runoff, are discussed as illustrations of some of the most important problems of modern hydrology.
PROBLEME PRINCIPAUX D E L'HYDROLOGIE M O D E R N E
RESUME : Le bilan #eau de--réservoirs, les relations réciproques entre l'eau de surface et l'eau souterraine, le bilag d'eau et de salinité des surfaces irriguées, le bilan d'eau de zones maréca- geuses et l'influence de l'homme sur l'écoulement sont discutés en les considérant c o m m e des illustrations de quelques-uns des plus importants problkrnes de l'hydrologie moderne.
PROBLEMAS S A B R E EL PRINCIPIO D E LA E V A P O T R A N S P I R A C I ~ N EN LOS BOSQUES
RESUMEN: C o m o ejemplo de alguno de los problemas m á s importantes que plantea la hidrológía moderna, en este documento se estudia el balance hidrológico de los embalses, la relación existente entre las aguas de superficie y Ias subterráneas, ei talance hidrológico y salino de las tierras irrigadas, el balance dihrológico dp laz sonas pantanosas y la influencia del hombre en los fenbmenos de la escorrentía.
OCHOBHbIE IIPOBJIEMbI COBPEMEHHOE ITEIAPOJIOI'ETkI
A H H O T ¿ì4 Ei Si PaCGM¿lTp€iB¿lSi HCTOPUH) pa3BUTHR rHApOJIOi'HU, aBTOp n p U X O A U T K. BbIBOAJT, -TO COBpeMeHHhIÜ & nepU0A XapaKTepH3y€TCSi BCB óonee IIlUpOKtUM BIIeApeHUeM MeTOAOB BOAHOI'O U CBR3aHHOI'O C H U M TenJIOBOI'O ó a n a n c o ~ B IlpaK- TUICy rHApOJIOrU¶eCKUX HCCJIe~OBaHUk, paC¶eTOB U IIPOrHOBOB.
n p U 3TOM XapaKTepHOfi OC06eHHOCThlO COBpeMeHIIOi'O nepUOJ(a B pa3BUTUU rUAp0- :
