The University of Arizona

Southwest Climate

satellite photo of the southwest

Hurricane Ileana approaches the Baja Penninsula on August 24th, 2006. Hurricanes play an important role in the climate of the Southwest in the late summer and early fall.
Credit: NASA

Climate of the Southwest
Changes in Southwest climate are occurring against a backdrop of overall aridity that relates to its landlocked position under a stream of dry, descending air. Temperature variability throughout the mountainous Southwest often relates to elevation changes, which also influence precipitation rates.

Seasonal Precipitation
Precipitation patterns are complex in the Southwest and vary by season as well as year. The sources and types of precipitation differ during the cool season and the warm season, as do their effects on the landscape. The Southwest also experiences different types of storms in different seasons.

Temperature Changes
Temperatures are projected to climb in the Southwest, with average annual temperatures increasing another couple degrees within the next quarter century and 5 to 8 degrees F by the end of the century. This prediction is within the range of what the region has already experienced in the past quarter century.

Precipitation Changes
Coupled with rising temperatures, the projected decline in precipitation seems likely to increase the region’s aridity in years to come. An analysis of Global Climate Model projections for the southwest quadrant of the United States suggests the region could become increasingly arid throughout the century. Extreme rainfall events are more likely to occur between dry spells.

Regional Variability
Even as overall aridity is likely to increase in the Southwest, precipitation rates will continue to vary when comparing seasons, years and even decades. Some of the influences on climate variability relate to seasonal patterns such as the summer monsoon, tropical storms including remnant hurricanes, and El Niño, with its influence on the jet stream.