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In order to provide water security in the twenty-first century, there is universal agreement that a continuation of current policies and extrapolation of trends is not an option. Also clear is that from both water supply and development perspectives, the world's arid and semi-arid regions are those currently and potentially experiencing the highest water stresses. One third of the world's land surface is classified as arid or semi-arid, and about half of all countries are directly affected in some way by problems of aridity. The hydrology of arid and semi-arid areas is also known to be substantially different from that in more humid regions. It is therefore essential that investigation methods appropriate to the former are developed and applied, and that strategies for arid and semi-arid region water resources development recognise the principal characteristics of in-situ hydrological processes.
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UNDERSTANDING WATER IN A DRY ENVIRONMENT
INTERNATIONAL CONTRIBUTIONS TO HYDROGEOLOGY
23
INTERNATIONAL ASSOCIATION OF HYDROGEOLOGISTS
Understanding Water in a Dry Environment Hydrological Processes in Arid and Semi-arid Zones Editor Ian Simmers Faculty of Earth and Life Sciences, Vrije Universiteit, Amsterdam
A.A. BALKEMA PUBLISHERS / LISSE / ABINGDON / EXTON (PA) / TOKYO
Library of Congress Cataloging-in-Publication Data Applied for
Financially supported by UNESCO as a contribution to the International Hydrological Programme IHP-V, Project 5.1
This edition published in the Taylor & Francis e-Library, 2005. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.”
Front cover: The Manga Grasslands—the ‘lake district’ of the Sahel. Rainfall of 400–500 mm/year in this area of Holocene sand dunes in northern Nigeria (Borno State) is sufficient to sustain a series of groundwater-fed lakes and fragile ecosystems. Recharge rates are around 40 mm/year, as estimated using both the Cl mass balance (unsaturated zone profiles) and groundwater models. During the 20-year Sahel drought of the 1970s and 1980s, many of the lakes dried completely or left a series of swamps. Photograph by W. Mike Edmunds, British Geological Survey, UK. Copyright # 2003 Swets & Zeitlinger B.V., Lisse, The Netherlands All rights reserved. No part of this publication or the information contained herein may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, by photocopying, recording or otherwise, without written prior permission from the publishers. Although all care is taken to ensure the integrity and quality of this publication and the information herein, no responsibility is assumed by the publishers nor the author for any damage to property or persons as a result of operation or use of this publication and/or the information contained herein. Published by: A.A. Balkema Publisher, A member of Swets & Zeitlinger Publishers www.balkema.ima.nl and www.szp.swets.nl. ISBN 0-203-97130-2 Master e-book ISBN
ISBN 90 5809 618 1 (Print Edition)
Contents
CONTRIBUTORS FOREWORD CHAPTER 1
CHAPTER 2
xiii xv
HYDROLOGICAL PROCESSES AND WATER RESOURCES MANAGEMENT — Ian Simmers Abstract 1.1 Introduction 1.2 Developments and Challenges 1.3 Arid and Semi-arid Zones 1.3.1 Geographical distribution 1.3.2 General hydrological characteristics 1.4 Guidebook Objectives and Adopted Approach 1.5 Conclusions and Recommendations References Selected Internet sites Bibliography RAINFALL IN ARID AND SEMI-ARID REGIONS —Jetse D. Kalma & Stewart W. Franks Abstract 2.1 Introduction 2.2 Rainfall Types and Mechanisms 2.3 General Circulation Aspects and the Distribution of Dry Climates 2.4 Mesoscale Climatic Syste