Where are the Droughts?
One of the pillars of the greenhouse apocalypse is the global warming will lead to a higher frequency, intensity, duration, and spatial extent of droughts in the future. This prediction is fairly easy to understand in terms of basic physical principles. Higher temperatures will lead to higher rates of potential evapotranspiration (PE), so even if rainfall stays the same or even increases slightly, the increase in PE will make droughts worse, make them last longer, make them more frequent, and make them expand their spatial extent. To make the matter even scarier, many climate models predict a decrease in precipitation in continental interiors, so with less rainfall, higher temperatures, and higher PE rates, drought frequency, intensity, spatial extent, and duration may substantially increase in places like the American heartland.
Literally dozens of articles have appeared in the scientific literature showing results that lead to the prediction of increased drought conditions in the central United States. The Intergovernmental Panel of Climate Change (IPCC) states in the Summary for Policymakers that “Increased summer continental drying and associated risk of drought” is “Likely, over most mid-latitude continental interiors” during the 21st century. In terms of seeing such a pattern in the observed climate record in the 20th century, the IPCC concludes it is “Likely, in a few areas.”
An important article appeared in the literature recently with some surprising results given the predictions of the climate models. Konstantinos Andreadis and Dennis Lettenmaier of the University of Washington have published a paper in Geophysical Research Letters entitled “Trends in 20th century drought over the continental United States,” and the results are peculiar—in light of climate model projections—to say the least. In the abstract, they write “Droughts have, for the most part, become shorter, less frequent, and cover a small portion of the country over the last century.”