Climate change and water resources – a national assessment

Climate change may have significant impacts on water resources use and management according to the Third National Climate Assessment.

In May 2014, the U.S. Global Change Research Program released The Third National Climate Assessment. The report details current and predicted impacts in the United States resulting from a changing climate. Over 300 experts contributed to the three-year effort to develop the report. Impacts are described as they affect geographic regions, and sectors such as health, water, forests and agriculture.

A major chapter covers how climate change impacts the water cycle (described in a companion article), water resource use and management, and adaptation opportunities and challenges.

Climate change may affect water demand and the ways water is used. Total water withdrawals from groundwater and surface water in the U.S. have leveled out over the past 30 years due to greater use efficiency. There are regional differences, however, with hotter and drier areas using more water per capita than other parts of the nation. Projected water demand increases follow that trend, with the greatest demand increases expected in the Southwest, Great Plains and Southeast, which are also the areas where water supply may be limited by decreasing precipitation.

Indeed, the combination of drought and water use change is affecting water supplies. A recent NASA study documented loss of freshwater reserves in the Colorado River Basin. Those trends are expected to continue.

The National Climate Assessment report highlights the critical importance of water for power plant cooling. This major use has already been affected in areas where water temperature is increasing and surface water supplies are diminishing. The impact is two-fold: reduced efficiency of power generation, and the ecological impacts (and regulatory limitations) of discharging warmer water to lakes and streams.

Increased frequency of flooding resulting from climate change is related to precipitation patterns, land use change (such as increasing area of impervious surfaces) and soil moisture. Although large-scale flooding is devastating, the report suggests that proactive management could help minimize risks and consequences.

The projected impacts of climate change will cause communities and water resource managers to face new risks and challenges that are not addressed in the current way those resources are managed. An example cited in the report from the Sacramento-San Joaquin River Delta in California highlights how flooding, seawater intrusion and changing water uses create significant management challenges. As with other water resources issues, the Southwest and the Southeast are particularly vulnerable to these challenges.

There are significant barriers, though. For example, the nation’s aging water drainage infrastructure, in the absence of efforts to increase resiliency and adaptive capacity, is ill equipped to handle increased storm runoff, leading to large increases in combined stormwater and sewage overflows into waterways.

Despite the challenges, communities can develop strategies to adapt to water cycle changes. In the past few years, many organizations at federal, state and local levels have started to incorporate climate change considerations into their ongoing water resource planning efforts in order to better understand the risks, implications and options of a changing water cycle.

For additional information about climate change, visit the Michigan State University Extension website on climate change and variability. A related MSU Extension article summarizes the other portion of this National Climate Assessment water resources chapter on changes in the water cycle.

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