World - Future & Past


     PDSI is Palmer Drought Severity Index, an indirect measure of soil moisture, relative to local baseline climate.  SC means self-calibrating.
"The index is the difference between the amount of precipitation required to retain a normal water-balance level and the amount of actual precipitation."
Light blue (-4.0 to -5.0) is extremely wet, red (+4.0 to +5.0) is extremely dry.
These 10-year averages did not occur in the model results before 2000,
Baseline climate period is probably a 30-year period before 1965.
    The maps display soil moisture, not precipitation.  With the same amount of rain and more evaporation, soil moisture decreases.

     Note that southern Europe is extremely dry by the 2060s and especially the 2090s, perhaps Saharan.
The USA is a lesser case of such dryness.
So are the much of the Amazon basin and the Andes, central America, southern Africa, and Australia.
    Note also the increasing soil moisture around the Acrtic.
Extremely wet conditions prevail in Indonesia, India, equatorial east Africa, Ecuador, and southern New Zealand.
    Aiguo Dai, Kevin Trenberth et al.

The two maps below are from IPCC 5, Technical Assessment (2013).


    Also available at for "A Global Dataset of Palmer Drought Severity Index for 1870–2002: Relationship with Soil Moisture and Effects of Surface Warming" in Journal of Hydrometeorology, December 1, 2004, pp. 1117-1130.

     Two key figures are excerpted below, with Dr. Fry's annotations.

     The slide below summarizes what has been happening with water tables, as groundwater is used ever more to cope with droughts and supply irrigation water for the Green Revolution.

Section Map: Droughts, Deserts & Fires