Climate Trivia: Dry Episodes in the Southwest
In the Southwest U.S., prolonged dry episodes are defined as periods of two months or longer when daily precipitation falls below one millimeter.
Trivia Question: Have such prolonged dry episodes become more or less common over the past 60 years?
a) More common
b) Less common
c) No change
The correct answer is b. Despite drought conditions in the late 1990′s and early 21st century, there appears to be an overall trend of fewer prolonged dry events in the Southwest since the 1950′s. This is especially true for the cold season (October through March), due to the more El Niño events in the eastern tropical Pacific Ocean over the study period. El Niño events work to steer the Northern Hemisphere storm track right over the desert Southwest. Also, since the mid-1970′s, the North Pacific Ocean has been in a “warm” phase of the Pacific Decadal Oscillation. Warm phases help to enhance the effects of El Niño events on Southwest rainfall. An overall warming, however, and thus an increase in soil evaporation, may be counteracting the effect this increase in precipitation has on streamflow levels.
Seasons: Winter, Spring, Summer, Fall
Source: McCabe, GJ et al. “Variability and trends in dry day frequency and dry event length in the southwestern United States.” Journal of Geophysical Research: Atmospheres 115 (2010): D07108.
