Finally, the question of climate change forcing was not comprehensively studied in this report. The analysis based on a single coupled model needs to be repeated using a suite of CMIP models. In this regard, it is useful to include here the conclusions of other assessment reports, using multiple models and other information than available in this 2012 study, on overall U.S. drought change during the last century and also on projections for the future. These appear in several recent National and International assessment reports. Among the climate issues addressed in 21 Synthesis and Assessment Products (SAPs), the U.S. Climate Change Science Program inquired into current understanding of the causes for high-impact drought events over North America. The 2008 SAP 1.3 report concluded that SST anomalies have been important in forcing some multiyear severe droughts over the U.S. during the last half-century, whereas short-term droughts (“flash droughts” having monthly-seasonal time scales) were judged to be mostly due to atmospheric variability, in some cases amplified by local soil moisture conditions. The report assessed that it is unlikely that a systematic change has occurred in either the frequency or area-coverage of drought over the contiguous US from the mid-20th century to the present. It is likely, according to that report, that anthropogenic warming has increased drought impacts over North America through increased water stresses associated with warming, though the magnitude of the effect was judged to be uncertain.
so flash droughts != systematic droughts
also flash droughts are potentially made worse by climate change.
