Running dry: The U.S. Southwest's drift into a drier climate state

Summary

This analysis applies weather type classification to 35 years of reanalysis data (1979–2014) to isolate the drivers of regional precipitation trends across the contiguous United States. The study reveals that the U.S. Southwest's documented drying is primarily attributable to shifts towards more frequent anticyclonic conditions over the North East Pacific, producing precipitation decreases of up to −25%, rather than to reductions in precipitation intensity. These findings have implications for understanding the climatological mechanisms underlying regional drought intensification.

UK applicability

The weather type methodology is potentially transferable to UK climate analysis, though the specific anticyclonic mechanisms driving Southwestern U.S. drying do not directly apply to British precipitation systems. However, the analytical approach of decomposing regional precipitation trends into frequency and intensity components may inform UK drought and flood risk assessments under climate change.

Key measures

Precipitation trends (1980–2010); weather type (WT) frequency changes; precipitation intensity changes; regional precipitation change percentages

Outcomes reported

The study quantified precipitation trends across the contiguous United States from 1980–2010, decomposing changes into contributions from shifts in weather type frequencies and changes in precipitation intensities. In the U.S. Southwest, weather type frequency changes (notably increased anticyclonic conditions) drove significant precipitation decreases of up to −25%, partially offset by increasing precipitation intensities.

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