Comparing Standard Drought Indices Against Streamflow and Vegetation Response Across Alaska

Abstract:

Unusually dry conditions over southeast Alaska in 2018/19 led to Alaska’s first extreme drought classification in the U.S. Drought Monitor, but some of the reported impacts were distinct from those seen in low- and mid-latitudes. The relative infrequency of drought in Alaska, along with other high-latitude locations, presents uncharted challenges for those who attempt to monitor its extent and severity. A recent Alaska drought workshop expressed the need to identify relevant drought indices and indicators; however, it is possible that the standard drought indices may not perform well in this region as drought, and its associated impacts, manifests differently. Assessing the standard drought indices against common drought indicators is a reasonable first step towards an improved understanding of drought characteristics across Alaska’s 13 diverse climate divisions. We computed three standard indices: standardized precipitation index, standardized precipitation evapotranspiration index, and the self-calibrating Palmer drought severity index using the National Centers of Environmental Information climate division temperature and precipitation over a 95-year period from 1925-2019. Each drought index was correlated against standardized streamflow anomalies at several USGS gages with relatively long records and satellite derived normalized difference vegetation index across all 13 climate divisions. The results of this research have the potential to enhance monitoring, improve drought representation, and consequently aid in more informed decision making during future drought events in Alaska.