Diagnostics of the Joint Behavior of US Summer Heat Waves and Drought: How Extreme was 2012?

The joint occurrence of summer drought and heat waves can substantially exacerbate the impacts of the former, as was vividly seen in the agriculture sector during the summer of 2012. While the joint incidence of these two extremes is clearly important, the two phenomena have typically been studied in isolation by researchers. Here we report on a diagnostic study of the joint occurrence of US summer heat waves and drought which considers multiple characteristics of both extremes. Using a variety of observational based datasets and simulated soil moisture from a land surface model the geographical distribution, seasonality, and frequency of this joint behavior across the contiguous is evaluated over the last 50-100 years. In addition, we demonstrate how incorporating humidity into the definition of a heat wave alters the above results and also quantify the conditional probability of a heat wave given the land surface condition (i.e. "drought" condition). Finally, the drought and heat waves during the summers of 2012 and 2011 are placed into historical perspective using the above-developed framework.