An Assessment of Drought Trends in the Contiguous United States Using the Drought Risk Atlas

The National Drought Mitigation Center’s Drought Risk Atlas (DRA) is being updated to include drought, precipitation, and temperature trends in the continental United States. The DRA, which is built on data from stations in the National Weather Service’s Cooperative Observer Network, has the best, most complete long-term histories of both precipitation and temperature, provided the data for the analysis. The Mann-Kendall tests for significance of time series trends was applied to each station for multiple drought indices, including the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI). By analyzing drought indices instead of raw precipitation/temperature data, the effects of seasonality within the time series on the robustness of trend tests should be reduced. The test were applied over multiple time scales, ranging from 30 years to over 100 years for some stations. Preliminary results suggest that, over the last 30-40 years, significant drying has been occurring in the Southern High Plains and Desert Southwest, while significant increases in precipitation have been found in the Northern High Plains, the Northeast, and the Ohio Valley.