Changes in Precipitation and Drought

Changes in Precipitation and Drought

Current NewsLarge-Scale Precipitation TrendsSnowfallDrought

For next class: Read IPCC AR5 Ch. 2 (pp. 194-201) on AsUlearn

Precipitation ChangesNo statistically significant linear trends in global precipitation from 1900 to 2012, but considerable variability exists.

Numerous challenges in measuring precipitation due to wind effects and accurate measurement of snowfall

Important changes in spatial patterns of precipitation:Wetter conditions across Amazon Basin and Patagonia in South AmericaDrier, then wetter across the African SahelChange in rainfall patterns may be tied to 1976-1977 Pacific Climate Shift

North Carolina State Average Precipitation

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1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

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Mean Precipitation 5-year Linear (Mean Precipitation) Poly. (Mean Precipitation)

Changes in SnowfallWinter precipitation has increased at high latitudes.Rising temperatures have generally resulted in rain rather than snow in locations and seasons where climatological average (1961-1990) temperatures were close to 0°C.Large increases in lake-effect snowfall since 1951 for locations near the Great Lakes, consistent with observed decrease in ice cover since the early 1980s.

Great Lakes SnowHow would a decrease in ice cover favor an increase in snowfall in the Great Lakes?

Drought TerminologyDrought: “prolonged absence or marked deficiency of precipitation” (Heim 2002 in IPCC AR4).

Agricultural drought relates to moisture deficits in the root zone of the soil that impacts crops.Meteorological drought is mainly a prolonged deficit of precipitation.Hydrologic drought is related to below normal streamflow, lake, and groundwater levels.PDSI (Palmer Drought Severity Index) is most commonly used drought index, using precipitation, temperature, and water content data to assess soil moisture.

Trends in PDSI 1900 to 2002

Red = DrierBlue = Wetter

U.S. Drought Monitorhttp://www.drought.unl.edu/dm/monitor.html