Changes in Precipitation and Drought
Current News
Large-Scale Precipitation Trends
Snowfall
Drought
For next class: Read IPCC AR5 Ch. 2 (pp. 194-201) on
AsUlearn
Record Cold in Canada
https://www.washingtonpost.com/news/c
apital-weathergang/wp/2017/03/07/biting-cold-poisedto-invade-eastern-u-s-thisweekend/?utm_term=.0ae766eb0f84
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 1976-1977 Pacific
Climate Shift
North Carolina State Average Precipitation
70
Precipitation (inches)
65
60
55
50
45
40
35
30
1895
1905
1915
1925
1935
1945
1955
1965
1975
1985
1995
Year
Mean Precipitation
5-year
Linear (Mean Precipitation)
Poly. (Mean Precipitation)
2005
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 (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 Snow
How would a decrease in ice cover favor an
increase in snowfall in the Great Lakes?
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.
Trends in PDSI
1900 to 2002
Red = Drier
Blue = Wetter
U.S. Drought Monitor
http://www.drought.unl.edu/dm/monitor.html