Snapshots from the New National Climate Assessment
After three years of intensive effort, research, writing, and review by hundreds of climate scientists, the latest update of the U.S. National Climate Assessment was released today. It includes many long, carefully prepared sectoral and regional studies, and covers the massive range of effects of climate change on the nation, including both changes already observed and expected in the future.
There are hundreds of pages of information, observations, projections, and conclusions to absorb – almost all of it bad news. Here, in short form and in the actual wording from the NCA (with page numbers from the “Highlights” summary report), are some of the most important conclusions related to U.S. water resources:
- Agriculture, water, energy, transportation, and more, are all affected by climate change. (p.33)
- Climate change is already affecting societies and the natural world (p. 32)
- Climate change affects more than just temperature. The location, timing, and amounts of precipitation will also change as temperatures rise. (p. 29, Figure)
- There are significant trends in the magnitude of river flooding in many parts of the United States. River flood magnitudes have decreased in the Southwest and increased in the eastern Great Plains, parts of the Midwest, and from the northern Appalachians into New England. (p. 26)
- Heavy downpours are increasing nationally, especially over the last three to five decades. The heaviest rainfall events have become heavier and more frequent, and the amount of rain falling on the heaviest rain days has also increased. Since 1991, the amount of rain falling in very heavy precipitation events has been significantly above…The mechanism driving these changes is well understood. (p. 25).
- Risks of waterborne illness, and beach closures resulting from heavy rain and rising water temperatures are expected to increase in the Great Lakes region due to projected climate change. (p. 36)
- Flooding along rivers, lakes, and in cities following heavy downpours, prolonged rains, and rapid melting of snowpack is exceeding the limits of flood protection infrastructure designed for historical conditions. (p. 38)
- Water quality and water supply reliability are jeopardized by climate change in a variety of ways that affect ecosystems and livelihoods. (p. 42)
- Annual precipitation and river-flow increases are observed now in the Midwest and the Northeast regions. Very heavy precipitation events have increased nationally and are projected to increase in all regions. The length of dry spells is projected to increase in most areas, especially the southern and northwestern portions of the contiguous United States. (p. 42)
- The Northeast has experienced a greater recent increase in extreme precipitation than any other region in the U.S.; between 1958 and 2010, the Northeast saw more than a 70% increase in the mount of precipitation falling in very heavy events. (p. 70)