In an unprecedented move, the President’s Science Advisor, Dr. John P. Holdren, has published a devastating 6-page debunking of one of the country’s leading climate confusionists, Roger Pielke Jr.
The bottom line is this, as explained by Dr Holdren:
“In my recent comments about observed and projected increases in drought in the American West, I mentioned four relatively well understood mechanisms by which climate change can play a role in drought. (I have always been careful to note that, scientifically, we cannot say that climate change caused a particular drought, but only that it is expected to increase the frequency, intensity, and duration of drought in some regions ― and that such changes are being observed.)”
These four mechanisms are:
In a warming world, a larger fraction of total precipitation falls in downpours, which means a larger fraction is lost to storm runoff (as opposed to being absorbed in soil).
In mountain regions that are warming, as most are, a larger fraction of precipitation falls as rain rather than as snow, which means lower stream flows in spring and summer.
What snowpack there is melts earlier in a warming world, further reducing flows later in the year.
Where temperatures are higher, losses of water from soil and reservoirs due to evaporation are likewise higher than they would otherwise be.