1. Changes in Precipitation and Drought
Current News
Large-Scale Precipitation Trends
Snowfall
Drought
For next class: Read IPCC AR5 Ch. 2 (pp ) on AsUlearn

2. Precipitation Changes
No 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 America
Drier, then wetter across the African Sahel
Change in rainfall patterns may be tied to Pacific Climate Shift

7. Changes in Snowfall
Winter precipitation has increased at high latitudes.
Rising temperatures have generally resulted in rain rather than snow in locations and seasons where climatological average ( ) 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.

8. Great Lakes Snow
How would a decrease in ice cover favor an increase in snowfall in the Great Lakes?

10. Drought Terminology
Drought: “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.

11. Trends in PDSI
1900 to 2002
Red = Drier
Blue = Wetter

12. U.S. Drought Monitor