There are two books (with one a two volume set) that provide an excellent summary of the threat of drought that we face even in the absence of human intervention in the climate system. Indeed, it is unlikely that mitigation of CO2 emissions alone would have much of an effect on our risk, since we are i) only effecting one aspect of the climate system by CO2 increases, and ii) the increased levels of atmospheric CO2 could be just as easily be moving us away from drought conditions, since there is no skill in year or longer time scales in predicting this climate regime.
The books are:
Wunder, J.R., F.W. Kaye and V. Carstensen (Editors), 2001:Americans View Their Dust Bowl Experience. University of Colorado Press.
Wilhite, D. A. (Editor), 1998: Dought A Global Assessment Volumes I and II. Routledge Hazards and Disasters Series. [this is, unfortunately, an expensive book so borrowing from the library is a good way to read it].
These books provide a sobering report on what has happened in the past in terms of drought effects.
For example, in Wunder et al on page 83 the text reads,
“A cloud of dust thousands of feet high, which came from drought-ridden states as far west as Montana 1500 miles away, filtered the rays of the sun for five hours yesterday, and New York was obscured to a half-light similar to the light cast by thr sun in partial eclipse.”
In the Wilhite book, in an excellent article starting on page 234 by Lisa Graumlich and Mrill Ingram entitled “Drought in the context of the last 1000+ years: Some surprising implications”, they write
“Our findings are sobering in that we see two droughts during medieval times lasting more than fifty years in which runoff was 40 per cent of twentieth century values”.
Such a drought, if it started today would last beyond 2057! Moreover, this drought occurred without a significant human role in altering the climate system.
Today, we also seem to be more vulnerable to even a very short term drought, as summarized in our paper
Pielke Sr., R.A., N. Doesken, O. Bliss, T. Green, C. Chaffin, J.D. Salas, C. Woodhouse, J.L. Lukas, and K. Wolter, 2005: Drought 2002 in Colorado – An unprecedented drought or a routine drought? Pure Appl. Geophys., Special Issue in honor of Prof. Singh, 162, 1455-1479, doi:10.1007/200024-005-2679-6.
For longer droughts, our planning is almost nonexistent. Seeking to prevent droughts by CO2 reductions is obviously not an effective way to approach our real risk to this climate regime.