Background
The authors begin their paper by stating that "drought can be regarded as one of the most damaging of natural disasters in human, environmental, and economic terms," and, therefore, it is not surprising that climate alarmists characteristically claim that drought conditions over the globe will occur more frequently and become more intense in response to global warming.

What was done
Sheffield and Wood investigated "variability and trends in soil moisture and drought characteristics, globally and regionally over the second half of the twentieth century," by means of "a global soil moisture dataset derived from a model simulation of the terrestrial hydrologic cycle" that was "driven by a hybrid observation-reanalysis-based meteorological dataset."

What was learned
The Princeton University researchers report that "an overall increasing trend in global soil moisture, driven by increasing precipitation, underlies the whole analysis, which is reflected most obviously over the western hemisphere and especially in North America," further stating that "trends in drought characteristics are predominantly decreasing," and that "concurrent changes in drought spatial extent are evident, with a global decreasing trend of -0.021% to -0.035% per year." They additionally note "there is a switch in later years to a drying trend, globally and in many regions, which is concurrent with increasing temperatures." However, this drying trend has not been strong enough to overpower the increasing trend of global soil moisture over the entire half-century of their analysis.

What it means
Even in the face of a warming trend that climate alarmists describe as having been unprecedented over the past one to two millennia, their predictions of more frequent and more severe concomitant drought have not been realized.