Global Characteristics of Flash Droughts

Flash drought, which usually refers to rapid soil moisture decrease over a short time period, can be categorized into two types: heat wave and precipitation deficit. The former type is caused by high temperatures which result in evapotranspiration increases while the latter is initiated by negative precipitation anomalies, which induce reductions in evapotranspiration.  The characteristics of these two types of flash droughts have been well explored over the conterminous U.S. (CONUS).  However, to date they have not been explored globally.  We examine here the nature of these two kinds of flash drought over the global land areas between 50°N and 50°S.  To do so, we perform a 60-year model simulation using the Variable Infiltration Capacity (VIC) model at 0.5° degree resolution for the period 1948-2008. We examine the relative frequency and season of occurrence of the two types of flash droughts, as well as trends in their rates of occurrence.