Early Warning

A significant advantage of examining drought from the evaporative perspective is the early warning that doing so affords. Because of the timing of the physical processes that link atmospheric forcing to, and signals from, the land surface (see Section 11.2) and our increased capabilities in monitoring these processes and the state of moisture stress in vegetation, we find that many of these tools provide information about drying anomalies or drought potential well before products that form the existing monitoring (and outlook) suite. As an example, Figure 11.4 shows the development of the flash drought of 2012 across the midwestern United States at regular intervals as monitored by the USDM, 2-week EDDI, 2-week ESI, and 2-week ESI RCI. The 2-week EDDI was clearly observing atmospheric drying for many weeks before the onset of the drought as measured by the USDM. In early June, EDDI, ESI, and ESI RCI were all showing rapidly deteriorating conditions across much of the central United States (e.g., Missouri, eastern Kansas, eastern Oklahoma, northern Arkansas, and Iowa), while the USDM only showed D0 and D1 drought classification (abnormally dry and moderate drought, respectively) over much of the same region. It was not until mid to late July, that the USDM introduced D3 and D4 categories (extreme drought and exceptional drought, respectively) over the region. This case study highlights the potential of metrics such as EDDI, ESI, and ESI RCI in providing early warning information about rapidly developing drought events (Hobbins et al. 2016; McEvoy et al. 2016a; Otkin et al. 2014, 2015, 2016).

 
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