Examining the relationship between drought development and rapid changes in the thermal-based Evaporative Stress Index

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Wednesday, 5 February 2014: 9:15 AM
Room C209 (The Georgia World Congress Center )
Jason A. Otkin, CIMSS/Univ. of Wisconsin, Madison, WI; and M. C. Anderson, C. Hain, and M. D. Svoboda

In this study, the ability of a new drought metric based on thermal infrared remote sensing imagery to provide early warning of an elevated risk for drought intensification is assessed. This new metric, called the Rapid Change Index (RCI), is designed to highlight areas undergoing rapid changes in moisture stress as inferred from weekly changes in the Evaporative Stress Index (ESI) generated using the Atmospheric Land Exchange Inverse (ALEXI) surface energy balance model. Two case study analyses across the central U.S. revealed that the initial appearance of negative RCI values indicative of rapid increases in moisture stress preceded the introduction of severe-to-exceptional drought in the United States Drought Monitor (USDM) by more than 4 weeks. Using data from 2000-2012, the probability of USDM drought intensification of at least 1, 2, or 3 categories over different time periods was computed as a function of the RCI magnitude. Compared to baseline probabilities, the RCI-derived probabilities often indicate a much higher risk for drought development that increases greatly as the RCI becomes more negative. When the RCI is strongly negative, many areas are characterized by intensification probabilities that are several times higher than the baseline climatology. These results show that rapid changes in the ESI provide useful drought early warning capabilities that could be used to alert stakeholders of an increased risk for drought development over sub-seasonal time scales.