Change in Northern Hemisphere Mid-Latitude Precipitation
All regions generally show an increase in the number of extreme precipitation events, but only the mid-latitudes show a robust increased trend in average precipitation. Global warming impacts precipitation through changes in atmospheric circulation and increases in water vapor and evaporation associated with warmer temperatures. Precipitation changes differ from region to region with dry areas generally getting drying and wet areas getting wetter.
Average US precipitation has increased since 1900, but there are regional differences, with some areas having larger increases, and others, decreases. More winter and spring precipitation is projected for the northern U.S., and less for the Southwest.
Extreme precipitation events (the upper 0.1 percent of daily rain events) have increased by about 33 percent over the past 100 years in the United States.
Global trends and projections
According to the IPCC, average precipitation has increased since 1901 over mid-latitude land areas across the globe. Mid-latitude regions are unique in this regard. For other latitudes, the IPCC states there is low confidence for any long-term positive or negative trends in average precipitation. Changes in the number of extreme precipitation events, however, are not restricted to mid-latitude land areas, and have been observed in regions across the globe.
If high greenhouse gas emissions continue, IPCC model simulations project that average precipitation in the mid-latitudes will likely increase in wet regions, and decrease in dry regions.