Outcomes of the 2011 Flood and 2012 Drought: Implications for Improving Drought Early Warning

Improved Monitoring and Indicator Development

The expert review panel commissioned by the Corps in the first post-flood analysis had six recommendations to mitigate or prevent impacts from similar high runoff events. One of these recommendations identified the need for better monitoring across the lower elevations of the Great Plains Upper Basin (above Sioux City, Iowa) and, in particular, improved understanding of the plains snowpack and soil moisture. The independent panel found that the Corps underestimated the volume of water in the plains in their forecasts and the amount of runoff that would result specifically from the plains snow. Monitoring both of these variables is difficult, however. For example, estimating runoff from plains snow can be confounded by issues with blowing snow, sublimation, and fine-scale differences in topography while soil moisture can vary based on soil type and several other variables that can differ over relatively small spatial scales. Estimating soil moisture is further complicated by the fact that there is currently a very limited number of soil moisture observing sites. In the winter of 2010 and early spring of 2011, the Corps knew the plains snowpack was above average and soils were wetter than normal, but it was difficult to know how this would ultimately affect runoff and runoff efficiency.

Both of these variables are critical (USACE 2012a) to understanding drought, as overprediction of runoff can result in potentially large impacts to streamflow and water supply, among other issues (such as impacts to rangelands). Improving understanding of both variables then was identified as a critical gap in knowledge, and this led to the formation of a team of climatologists and federal scientists from across the region to develop a series of recommendations (USACE 2013) for improving the snow and soil moisture monitoring in the Upper Missouri Basin.

The goal of the assessment, and the ultimate recommendations, was to improve the monitoring infrastructure and methodology so that realtime estimates of snow water equivalent and soil moisture, and the runoff from the melted snow, could be generated specifically for the northern plains (i.e., North Dakota, South Dakota, and parts of eastern Wyoming and Montana). The data would be used to inform forecasts of both floods and droughts. Recommendations from this report were ultimately included in the Water Resources Reform and Development Act of 2014 (WRRDA, P.L. 113-121) and subsequently in the NIDIS strategic plan for developing a drought early warning system in the Missouri Basin. As of publication, funding is still being sought to build the network in the Upper Basin.

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