Changes in Summer-to-Winter Precipitation Ratios in the United States Before and After the Onset of Global Warming

Authors: Walker Skeeter*, University of Delaware, Wesley Skeeter, The University of British Columbia, Brent Skeeter, Salisbury University
Topics: Climatology and Meteorology, Quantitative Methods
Keywords: Climatology, Climate Change, Hydroclimatology
Session Type: Poster
Day: 4/4/2019
Start / End Time: 8:00 AM / 9:40 AM
Room: Lincoln 2, Marriott, Exhibition Level
Presentation File: No File Uploaded


It is well established that average global surface temperatures have increased since around 1980. Positive feedbacks due to decreasing albedo associated the loss of snow and ice surfaces in high latitude areas are causing the equator-to-pole temperature gradient to decrease. In theory, this should lead to decreases in wintertime wind speeds and cyclonic activity across the Northern Hemisphere, which may lead to a decrease in wintertime precipitation. Counter to this, warmer air can “hold” more moisture, so winter cyclonic systems may produce more precipitation. Thus, determining changes in mid-latitude winter precipitation in association with global warming is not straightforward. Summer precipitation in the mid-latitudes is mostly convective. Higher summer temperatures and water vapor capacity should lead to increased summer precipitation totals in some areas. The uncertainty regarding seasonal changes in precipitation totals in the mid-latitudes associated with global warming leads us to examine whether the ratio of summer-to-winter precipitation totals has changed in recent decades. Summer-to-winter precipitation ratios across the conterminous United States were examined using over 1000 USHCN stations for the periods of 1948-1977 (pre-warming) and 1988-2017 (post-warming). Statistical analyses indicate significant regional differences in changing ratios across the country. The greatest decreases in mean winter precipitation was observed in the coastal Pacific Northwest (60 mm) while modest increases were observed in southern regions. Changes in summer precipitation were more variable, with the greatest increases in New England (37 mm). Changes in the ratio of summer-to-winter precipitation were greatest in the Desert Southwest and New England.

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