Climate change has already altered, and will
continue to alter, the water cycle, affecting where, when, and how
much water is available for all uses.
Floods and droughts are likely to become more
common and more intense as regional and seasonal precipitation patterns
change, and rainfall becomes more concentrated into heavy events (with
longer, hotter dry periods in between).
Precipitation and runoff are likely to
increase in the Northeast and Midwest in winter and spring, and
decrease in the West, especially the Southwest, in spring and summer.
In areas where snowpack dominates, the timing
of runoff will continue to shift to earlier in the spring and flows will
be lower in late summer.
Surface water quality and groundwater quantity will be affected by a changing climate.
Climate change will place additional burdens on already stressed water systems.
The past century is no longer a reasonable guide to the future for water management.
Changes in the water cycle, which are consistent with the warming observed over the past several decades, include:
For the future, marked regional differences are projected, with increases in annual precipitation, runoff, and soil moisture in much of the Midwest and Northeast, and declines in much of the West, especially the Southwest.
Climate change impacts include too little water in some places, too much water in other places, and degraded water quality. Some locations will be subject to all of these conditions during different times of the year. Water cycle changes are expected to continue and will adversely affect energy production and use, human health, transportation, agriculture, and ecosystems (see table on page 50).
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