Water Resources This page intentionally left blank Water Resources Science and Society GEORGE M. HORNBERGER & DEBRA PERRONE JOHNS HOPKINS UNIVERSITY PRESS Baltimore © 2019 Johns Hopkins University Press Special discounts are available for bulk purchases of this All rights reserved. Published 2019 book. For more information, please contact Special Sales at Printed in Canada on acid- free paper 410-516-6936 or specialsales@press . jhu . edu. 9 8 7 6 5 4 3 2 1 Johns Hopkins University Press uses environmentally Johns Hopkins University Press friendly book materials, including recycled text paper that 2715 North Charles Street is composed of at least 30  percent post- consumer waste, Baltimore, Mary land 21218-4363 whenever pos si ble. www . press . jhu . edu Library of Congress Cataloging-in-Publication Data Names: Hornberger, George M., author. | Perrone, Debra, author. Title: Water resources : science and society / George M. Hornberger and Debra Perrone. Description: Baltimore : Johns Hopkins University Press, 2019. | Includes bibliographical references and index. Identifiers: LCCN 2019004930 | ISBN 9781421432953 (paperback : alk. paper) | ISBN 1421432951 (paperback : alk. paper) | ISBN 9781421432960 (electronic) | ISBN 142143296X (electronic) Subjects: LCSH: Water-supply. Classification: LCC TD345 .H59 2019 | DDC 333.91—dc23 LC record available at https://lccn.loc.gov/2019004930 A cata log rec ord for this book is available from the British Library. CONTENTS Preface vii I Water Availability: A Physical Science Primer 1. The Hydrological Cycle 3 2. Surface Water Resources 20 3. Groundwater Resources 40 4. Soil Water Resources 60 II Demand- Side Sectors 5. Agricultural Water Use 75 6. Energy Water Use 102 7. Domestic Water Use 130 8. Environmental Water Use 144 III Anthropogenic D rivers of Change 9. Population 159 10. Climate Change 179 11. Water Law 190 12. Water Quality 209 IV Water Resources Supply and Demand in Context 13. Opportunities for Water Management 229 Appendix: Units, Dimensions, and Conversions 251 Glossary 257 Index 265 This page intentionally left blank PREFACE How much water is there on Earth, and how is it distributed over space and time? How much w ater do h umans need, and how much does the environment need? What changes in the f uture w ill affect the ability of people to use water sustainably? Water moves through the global hydrological cycle and supplies the fresh w aters contained in rivers, lakes, groundwater, and soil water and that are used by plants and animals. Basic information about the volumes and flows of these water resources is the un- derpinning for understanding the supply sector for w ater and is the subject of Part I of this book. Several primary uses of water that are essential for civilization are to grow food, produce energy, provide needs for drinking, bathing, cooking, and so on, and maintain healthy ecosystems. These needs for water are cornerstones of the demand sector for water. The material for Part II provides a primer on each sector and introduces trade-offs involving reliability, economics, the en- vironment, and water use. Matching supply and demand is the essence of water resources management. As we move farther into the twenty- first c entury, pressures on w ater resources w ill increase and affect management options. Population growth, climate change, implementations of water law, and deterioration of water quality all will act as con- straints. These are topics covered in Part III. One last question remains: How can knowledge about physical and social systems be harnessed to manage w ater resources? The final chapter of the book provides an overview of opportunities to manage water sustainably in the future in the face of unavoid- able trade- offs. Our goal is to introduce twenty- first century water resources issues to undergraduate students from across a wide spectrum of disciplines, including natu ral (environmental) sciences, social viii Preface sciences, and humanities. This book fits between the two bookends of being highly technical for advanced hydrology, engineering optimization, or law courses and being a completely descriptive summary of issues. It covers basic methods and includes illustra- tive quantitative calculations and qualitative think-p ieces. It covers calculations related to water bud gets. It covers data and calcula- tions used to inform decisions about allocation of water resources. It contains case studies that illustrate key princi ples of water law. Several conventions are used to make the text user friendly. Each chapter concludes with a summary of key points. Boxes are included in many chapters to illustrate concepts introduced in the main text. Each chapter has a set of example prob lems based on the material covered. An appendix provides a review of units, dimensions, and conversions useful for addressing each chapter’s example prob lems. And, fin ally, terms in boldface are included in the glossary. We are grateful for the comments from our editors, colleagues, anonymous reviewers, and f amily. We are thankful to our students and teaching assistants for test- driving the material and working through the prob lem sets. This book was a true collaboration with each author contribut- ing equally. I Water Availability: A Physical Science Primer