Federal Coordinating Lead Authors:
Thomas Johnson, U.S. Environmental Protection Agency
Peter Colohan, National Oceanic and Atmospheric Administration
Chapter Lead:
Upmanu Lall, Columbia University
Chapter Authors:
Amir AghaKouchak, University of California, Irvine
Sankar Arumugam, North Carolina State University
Casey Brown, University of Massachusetts
Gregory McCabe, U.S. Geological Survey
Roger Pulwarty, National Oceanic and Atmospheric Administration
Review Editor:
Minxue He, California Department of Water Resources
USGCRP Coordinators:
Kristin Lewis, Senior Scientist
Allyza Lustig, Program Coordinator


Water security in the United States is increasingly in jeopardy. Ensuring a reliable supply of clean freshwater to communities, agriculture, and ecosystems, together with effective management of floods and droughts, is the foundation of human and ecological health. The water sector is also central to the economy, contributing significantly to the resilience of many other sectors, including agriculture (Ch. 10: Ag & Rural, KM 2 and 4), energy (Ch. 4: Energy), urban environments (Ch. 11: Urban), and industry. The health and productivity of natural aquatic and wetland ecosystems are also closely linked to the water sector (Ch. 7: Ecosystems, KM 1).

Changes in the frequency and intensity of climate extremes relative to the 20th century5,6 and deteriorating water infrastructure are contributing to declining community and ecosystem resilience. Climate change is a major driver of changes in the frequency, duration, and geographic distribution of severe storms, floods, and droughts (Ch. 2: Climate). In addition, paleoclimate information (reconstructions of past climate derived from ice cores or tree rings) shows that over the last 500 years, North America has experienced pronounced wet/dry regime shifts that sometimes persisted for decades.2 These shifts led to protracted exposures to extreme floods or droughts in different parts of the country that are extraordinary compared to events experienced in the 20th century. Operational principles for engineering, design, insurance programs, water quality regulations, and water allocation generally have not factored in these longer-term perspectives on historical climate variability or projections of future climate change.7,8 While there has been much discussion on the need for climate adaptation, the design and implementation of processes that consider near- and long-term information on a changing climate are still nascent.9,10,11

Water systems face considerable risk even without anticipated future climate changes. Gains in water-use efficiency over the last 30 years have resulted in total U.S. water consumption staying relatively constant.12 Gains in efficiency are most evident in urban centers.13 However, limited surface water storage and a limited ability to make use of long-term drought forecasts and to trade water across uses and basins have led to the significant depletion of aquifers in many regions of the United States.1 Aging and deteriorating dams and levees14 also represent an increasing hazard when exposed to extreme or, in some cases, even moderate rainfall. Several recent heavy rainfall events have led to dam, levee, or critical infrastructure failures, including the Oroville emergency spillway in California in 2017,15 Missouri River levees in 2017, 50 dams in South Carolina in October 201516 and 25 more dams in the state in October 2016,17 and New Orleans levees in 2005 and 2015.18 The national exposure to this risk has not yet been fully assessed.

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