Trends in 20th century drought over the continental United States


Andreadis, K.M., Lettenmaier, D.P. 2006. Trends in 20th century drought over the continental United States. Geophysical Research Letters 33, L10403, doi:10.1029/2006GL025711.


We used a simulated data set of hydro-climatological variables to examine for 20th century trends in soil moisture, runoff, and drought characteristics over the conterminous United States (U.S.). An increasing trend is apparent in both model soil moisture and runoff over much of the U.S., with a few decreasing trends in parts of the Southwest. The trend patterns were qualitatively similar to those found in streamflow records observed at a station network minimally affected by anthropogenic activities. This wetting trend is consistent with the general increase in precipitation in the latter half of the 20th century. Droughts have, for the most part, become shorter, less frequent, and cover a smaller portion of the country over the last century. The main exception is the Southwest and parts of the interior of the West, where, notwithstanding increased precipitation (and in some cases increased soil moisture and runoff), increased temperature has led to trends in drought characteristics that are mostly opposite to those for the rest of the country especially in the case of drought duration and severity, which have increased.