Climatic Droughts conditions in US during the Past Century

Abstract:

It has been debated whether drought has become more severe under climate change. Different data sources of Palmer Drought Severity Index (PDSI) have been used to address the issue. This study assesses drought frequency in the continental US using two PDSI datasets (generated by Sheffield et al., 2012 and Dai, 2013). The uni-variate return period for three drought characteristics (duration, severity and intensity) and the bi-variate return period based on the Copulas distribution for combinations of duration and severity/intensity are generated in a time series of sequential moving windows with a horizon of 40 years (1900-1939, 1901-1940, …, 1973-2012). This time series will allow us to analyze both short-term (e.g., 10-year) and long-term (e.g., 100-year) droughts. A change point detection method is applied to the generated time series to detect both abrupt and gradual changes of drought in terms of return periods. The detection results can tell whether short-term (e.g., 5-year return period) or long-term (e.g., 100-year return period) droughts have occurred with larger intensity, longer duration, and/or higher severity and when a trend, if existing, in those characteristics began or stopped (e.g., the increasing trend of intensity levels at all return periods began around 1970 at a location in Northern California as shown in Figure 1a). We find some different results when comparing short- and long-term drought events. For examples, the levels of duration, severity and intensity for short-term (e.g., 5-year and 10-year return period) and long-term (e.g., 50-year and 100-year return period) drought events experienced different trends in central Colorado (Figure 1b). This presentation will provide the results for the entire continental U.S. and especially the spatial heterogeneity and distribution of the changes.

References

A. Dai, Nature Climate Change, 3, 52-58 (2013).

J. Sheffield, E.F. Wood, M. L. Roderick, Nature, 491, 435-438 (2012)

Figure 1. Levels of duration, severity and intensity at different return periods in sequential moving windows (1900-1939, 1901-1940, …, 1973-2012) in a grid of Dai (2013) in (a) Northern California and (b) Central Colorado