McCabe, G.J., Wolock, D.M. and Austin, S.H. 2017. Variability of runoff-based drought conditions in the conterminous United States. International Journal of Climatology 37: 1014-1021.
Introducing their work, McCabe et al. (2017) write that “there is concern that climate change may substantially affect the frequency and duration of drought.” And while further noting that there have been relatively few studies that have examined hydrologic drought on the spatial scale of the conterminous United States (CONUS), the three scientists set out to do just that.
More specifically, they analyzed monthly runoff values estimated from a monthly water-balance model for 2109 hydrologic units across the U.S. over the water years (October-September) 1901-2014. In addition, they sought to determine the climate factors responsible for driving drought variability.
McCabe et al. describe their findings as follows: “Results indicated that (1) the longest mean drought lengths occur in the eastern CONUS and parts of the Rocky Mountain region and the northwestern CONUS, (2) the frequency of drought is highest in the southwestern and central CONUS, and lowest in the eastern CONUS, the Rocky Mountain region, and the northwestern CONUS, (3) droughts have occurred during all months of the year and there does not appear to be a seasonal pattern to drought occurrence, (4) the variability of precipitation appears to have been the principal climatic factor determining drought, and (5) for most of the CONUS, drought frequency appears to have decreased during the 1901 through 2014 period” (see figure below).
McCabe et al. also note that (6) “changes in drought length were small, and large regions of coherent decreases or increases in drought length are not apparent.”
In light of all of the above findings, it would appear that instead of making droughts worse, the global warming/climate change experienced over the past century appears to have ameliorated them. And that finding stands in stark opposition to model-based predictions of future drought, which foresee them getting more frequent and severe as the CO2 concentration of the atmosphere rises.
Figure 1. Number of hydrologic units (HUs) across the U.S. with drought conditions by month and year.