ContentsWORLD WATER RESOURCES A NEW APPRAISAL AND ASSESSMENT FOR THE 21ST CENTURY A summary of the monograph World Water Resources prepared in the framework of the International Hydrological Programme bY Igor A. Shiklomanov Director State Hydrological Institute St Petersburg, RussiaThe designations employed and the presentation of material throughout the publication do not imply the expression of any opinion whatsoever on the part of UNESCO concerning the legal status of any country, territory, city or area or its authorities, or concerning the delimitation of its frontiers or boundaries Published in 1998 by the United Nations Educational, Scientific and Cultural Organization 7 Place de Fontenoy, 75352 Paris 07 SF’ Designed and produced by RPL Design, Milton Keynes, UK 0 UNESCO 1998Preface In the framework of UNESCO’s International Hydrological Programme (IHP), a monograph on world water resources has been prepared by Professor I. Shiklomanov and his team at the State Hydrological Institute, Saint Petersburg, Russian Federation. It is a result of a decade of international co-operative research and provides an updated assessment of the freshwater resources of the world at the beginning of the 21st Century and also addresses the problems of availability, protection and management of water resources. This brochure is a summarized version of the monograph and is designed to help decision-makers, administrators and the general public to fully understand the challenges in the domain of water which we are facing today and which need to be met tomorrow. It presents, in summarized form, the distribution of world water resources, their main basic components, their present water supply, agricultural and industrial use for a forecast for water use according to increasing demand, the impact of human activity on the availability of water together with recommendations for the future. The brochure also clearly shows that much is still to be achieved and that many aspects need to be improved, in particular, global hydrological networks and the collection and processing of data to ensure greater accuracy and reliability in water resources assessment. Worldwide efforts need to be made. There is a pressing need for even closer co-operation amongst scientists, international and non-governmental organizations dealing with hydrology and water resources so that water resources assessment capabilities can be improved from national through regional to global levels. We hope that the information the brochure contains will prove useful for understanding the problems raised by an ever-increasing demand for water, especially in areas where the freshwater supply is limited, such as arid and semi-arid regions. The monograph will be published in UNESCO’s International Hydrology Series. A. Szollosi-Nagy Secretary International Hydrological ProgrammeContents INTRODUCTION DEFINITION OF FRESHWATER RESOURCES 4 DISTRIBUTED VARIABILITY OF EARTH’S WATER RESOURCES The basic measurements: assessment methodologies Continental, regional and country differences Temporal/spatial variations in renewable water resources River basins and runoff to the oceans River runoff and groundwater 7 7 9 11 13 15 WATER USE IN THE WORLD : PRESENT SITUATION/FUTURE NEEDS Municipal water use Water in industry Water in agriculture Surface water reservoirs Forecasting global water use Future water requirements Resources in relation to demand 16 17 18 19 21 22 24 26 WATER AVAILABILITY AND DEFICITS 27 MAN’S IMPACT ON CLIMATE AND WATER 28 SAFEGUARDING THE FUTURE 34 CONCLUSIONS 36 2 Acknowledgements The author considers it his duty to express his sincere gratitude to his colleagues, workers of SHI. Due to their great efforts it became possible to obtain new data on the dynamics of water resources of the Earth and their use. Among them are heads of laboratories of SHI: Prof Vladimir I. Babkin and Dr. Vladimir Yu. Georgiyevsky; senior scientists: Dr. Tamara Ye. Grigorkina, Dr. Natalia V. Penkova, Dr. Irena I’. Zaretskaya; scientists: Anna V. Izmailova and Valentina I? Yunitsyna; leading engineers: Tatiana V. Grube, Irena A. Nikiforova, Tatiana I. Printseva, Elena L. Skoryatina and Valentina G. Yanuta.Introduction . ..Water is the most widely distributed substance on our planet.. . Water resources occupy a special place among other natural resources. Water is the most widely distributed substance on our planet: albeit in different amounts, it is available everywhere and plays a vital role in both the environment and human life. Of most importance is fresh water, Human life itself is impossible without it because it can be substituted by nothing else. Human beings have always consumed fresh water and used the various natural surface water bodies for a whole range of purposes. For many hundreds of years man’s impact on water resources was insignificant and entirely of a local character. The magnificent properties of natural waters - their renovation during the water cycle and their ability for self-purification - allowed a state of relative purity, quantity and quality of fresh waters to be retained for a long time. This gave birth to an illusion of immutability and inexhaustibility of water resources, considered as a free gift of the natural environment. Under these preconceptions a tradition has arisen of a careless attitude in the use of water resources, along with a concept that only minimum expense is required for either the purification of waste water or for the protection of natural water bodies. The situation has changed drastically during recent decades. In many parts of the world the unfavourable results of man’s long-term - often unreasonable - activities, have now been discovered. This concerns both the direct use of water resources and also the surface