Keywords: climate change, southwest, climate variability, warming, drought, streamflow, projection, future, temperature, precipitation, emission scenario
Natural climate variability is a prominent factor that affects many aspects of life, livelihoods, landscapes, and decision-making across the Southwestern U.S. (Arizona, California, Colorado, Nevada, New Mexico, and Utah; included are the adjacent United States-Mexico border and Southwest Native Nations land). These natural fluctuations have caused droughts, floods, heat waves, cold snaps, heavy snow falls, severe winds, intense storms, the battering of coastal areas, and acute airquality conditions. And as a region that has experienced— within the relatively short time span of several decades—rapid increases in human population (Figure 1.1), significant alterations in land use and land cover, limits on the supplies of water, longterm drought, and other climatic changes, the Southwest can be considered to be one of the most “climate-challenged” regions of North America. This document summarizes current understanding of climate variability, climate change, climate impacts, and possible solution choices for the climate challenge, all issues that are covered in greater depth in Assessment of Climate Change in the Southwest United States1 .