Comparative hydrology An ecological approach to land and water resources Edited by Malin Falkenmark and Tom Chapman Unesco Contents page Introduction 1 M. Falkenmark A. Theory and methodology 1. Comparative hydrology - a new concept 8 M. Falkenmark 2. Hydrological systems and processes 35 T. Chapman 3. Classifi cation of regions 50 T. Chapman 4. Measurement and estimation of hydrological 56 processes G. Kovacs 5. Human interventions in the terrestrial water cycle 77 G. Kovacs, F. Zuidema & J. Marsalek 6. Techniques for inter-regional comparison 95 G. Kovacs B. Areas with catchment response 7. Sloping land with snow and ice 106 H. Lang 8. Humid temperate sloping land 119 N. Arnell 9. Dry temperate sloping land 151 M. Falkenmark 10. Humid warm sloping land 161 L. Oyebande & J. Balek 11. Dry warm sloping land 196 J. Colombani & J.Rodier 12. Small high islands 210 E. Wright C. Flatlands 13. Flatlands with snow and ice 231 G. Chernogaeva 14. Humid temperate fl atlands 236 G. Chernogaeva 15. Dry temperate fl atlands 240 M. Fuschini Mejia 16. Humid warm fl atlands 251 J. Balek 17. Dry warm fl atlands 263 J. Colombani & J. Rodier 18. Small fl at islands 277 E. Wright 19. Deltas and coastal areas 295 A. Volker References .. Index .. Symbols The symbols used in this text have been selected to form a consistent unambiguous set that is as far as possible in conformity with other Unesco publications and international standards. Sym- bols used only once are defi ned in the text; those used more generally are listed below. Where more than one meaning is given, the correct interpretation should be clear from the context; no chapter has a symbol with more than one meaning. Many symbols are modifi ed by subscripts, to indicate a more particular meaning. Subscripts used more than once are also listed below. General symbols Symbol Meaning a,b Parameters in Montanari equation c Concentration d Depth (of water-table) D Saturation vapor defi cit E Evapotranspiration Eo Potential evaporation G Sensible heat fl ux into ground h Piezometric head, or water depth in a storage H Sensible heat fl ux from surface to atmosphere i Rainfall intensity I Infi ltration depth K Parameter in fl ow routing eqyations, or hydraulic conductivity (permeability) m Index in nonlinear fl ow routing equation n Porosity ns Specifi c storage P Precipitation depth q Flux Q Discharge ra Wind-dependent resistance in combination equation rs Stomatal resistance in combination equation R Groundwater recharge (as a depth) Rn Net radiation S Stemfl ow, or rate of change of saturation vapor pressure with temperature, or groundwater storage coeffi cient t Time T Duration, or throughfall depth, or transmissivity of an aquifer Tr Turnover time V Volume a Parameter in Priestley-Taylor equation b Bowen ratio g Psychrometric constant D Change in value of following quantity l Latent heat of vaporization of water r Density General subscripts g Groundwater i Interception p Pan (evaporation) s Surface u Unsaturated zone y Year Preface Although the total amount of water on earth is generally assumed to have remained virtually con- stant, the rapid growth of population, together with the extension of irrigated agriculture and indus- trial development, are stressing the quantity and quality aspects of the natural system. Because of the increasing problems, man has begun to realize that he can no longer follow a “use and discard” philosophy - either with water resources or with any other natural resources. As a result, the need for a consistent policy of rational management of water resources has become evident. Rational water management, however, should be founded upon a thorough understanding of water availability and movement. Thus, as a contribution to the solution of the world’s water problems, Unesco, in 1965, began the fi rst world-wide programme of studies of the hydrological cycle - the International Hydrological Decade (IHD). The research programme was complemented by a major effort in the fi eld of hydrological education and training. The activities undertaken during the Decade proved to be of great interest and value to Member States. By the end of that period, a majority of Unesco’s Member States had formed IHD National Committees to carry out relevant national activities and to participate in regional and international co-operation within the IHD pro- gramme. The knowledge of the world’s water resources had substantially improved. Hydrology became widely recognized as an independent professional option and facilities for the training of hydrologists had been developed. Conscious of the need to expand upon the efforts initiated during the International Hydrological Decade and, following the recommendations of Member States, Unesco, in 1975, launched a new long-term intergovernmental programme, the International Hydrological Programme (IHP), to follow the Decade. Although the IHP is basically a scientifi c and educational programme, Unesco has been aware from the beginning of a need to direct its activities toward the practical solutions of the world’s very real water resources problems. Accordingly, and in line with the recommendations of the 1977 United Nations Water Conference, the objectives of the International Hydrological Programme have been gradually expanded in order to cover not only hydrological processes considered in interrelation- ship with the environment and human activities, but also the scientifi c aspects of multipurpose utilization and conservation of water resources to meet the needs of economic and social develop- ment. Thus, while maintaining IHP’s scientifi c concept, the objectives have shifted perceptibly towards a multidisciplinary approach to the assessment, planning, and rational management of water resources. As part of Unesco’s contribution to the objectives of the IHP, two regular publication series are issued: “Studies and Reports in Hydrology” and “Technical Papers in Hydrology”. Occasionally, documents such as the present one are produced by special arrangements with IHP National Com- mittees or other national entities associated with the production of the basic report and are made available for distribution from the IHP headquarters at Unesco, Paris. This textbook Comparative Hydrology owes much to the enthusiasm, devotion and hard work of the two editors Malin Falkenmark and Tom Chapman, and their collaboration is acknowledged with gratitude. Special thanks go to Professor Chapman who devoted very many hours to devel- opment of the text and diagrams in computer-compatible form and to preparation of the book as camera-ready copy. Dedication This book is dedicated to the memory of academician Dr. Gyorgy Kovacs, former Director-General of the Hungarian Water Resources Research Centre (VITUKI), Past-President of the International Association for Hydrological Sciences (IAHS), and Chairman of the IHP Council from 1981 to 1983, who died in Budapest on 21 April 1988. George Kovacs enthusiastically supported the concept of a book on Comparative Hydrology and was a member of the Editorial Board which had the task of developing an unformed idea into a structured text. Through his broad knowledge and comprehensive understanding of the differences between hydrological processes and systems in different parts of the world, his contribution was critical in the selection of the general approach and regional classifi cations adopted in this book. He personally wrote two chapters and contributed to others, and the references to his work which have been cited in many chapters are a testimony to his contribution to what he felt is a new and exciting development in hydrology. Editors’ foreword This book has been made possible only through the interest of the Intergovernmental Council for the International Hydrological Programme (IHP), the International Association of Hydrological Sciences (IAHS) and the World Meteorological Organization (WMO); and in particular, all the distinguished experts in hydrology with experience from different zones of the world who have participated as authors. The Council transferred the task of implementing the book to an Editorial Board with the following members: Professor Malin Falkenmark, Swedish Natural Science Research Council, Stockholm, Sweden Professor Tom Chapman, University of New South Wales, Sydney, Australia Ms. G.M. Chernogaeva, National IHP Committee, Moscow, USSR Mr. J. Colombani, ORSTOM, Bondy, France Dr. G. Kovacs, Research Centre for Water Resources Development, Budapest, Hungary Professor Lekan Oyebande, University of Lagos, Abeokuta, Nigeria Dr. Arthur J. Askew, WMO, Geneva, Switzerland Mr. W.H. Gilbrich, Unesco, Paris, France. After the outline had been fi rst defi ned by the Editorial Board, Unesco invited selected experts to provide preliminary chapter texts to be discussed at an IHP Workshop on Comparative Hydrology, held in Budapest as part of the IAHS Assembly in July 1986. Many national IHP Committees contributed additional material which was included in the text. The fi nal authors were invited to deliver their texts by February 1987. The Editorial Board, meeting in Paris in May 1987, assigned the fi nal editing of the text to the two of us. Thanks to a research grant from the Swedish Natural Science Research Council, an editiorial offi ce was organized in Stockholm during the fall of 1987. Now that we are about to forward the fi nal text to the IHP Secretariat for publication, we wish to make some explanatory comments. We are fully aware of a number of defi ciencies in the textbook which could not be avoided at the present time. In spite of - or maybe due to - the fact that so much more has been written about the temperate zone than about the various subzones of the warm and hot regions, considerable dif- fi culties were found in locating authors willing to reduce the material into the required format of a single chapter. We acknowledge the assistance of the Institute of Hydrology in Wallingford in fi nding the fi nal author and reviewers for the chapter on humid temperate sloping land, which is a contribution from IHP Project 6.1 Flow Regions from Experimental and Network Data.