Progress in predicting May‒July (MJJ) seasonal rainfall over the south central US: implications for improving summer drought preparedness in Texas

The Texas Water Development Board (TWDB) is the state agency tasked with developing and securing water for the state. The TWDB prepares a state water plan, based on 16 regional water plans, addressing the needs of all water user groups in the state during a repeat of the drought of record. In response to the exceptional drought of 2011, new rules were adopted for TWDB's water planning process in 2012 requiring all regional water planning groups to include a chapter dedicated to drought response information, activities, and recommendations. The water planning regions are required to seek better information on drought action-triggers, and to provide recommendations for each existing water source by identifying drought triggers and response strategies. We report on how we tested and communicated information about a process-based statistical model to predict May‒July (MJJ) rainfall over the Southern Great Plains based on persistent drought-inducing atmospheric circulation patterns and surface dryness in spring. Given that the statistical model can predict MJJ rainfall over the region in spring, with skill levels acceptable to decision makers in Texas, we present information on our plans for applying the empirical seasonal forecast tool to derive probabilistic forecasts of whether reservoir storage levels will be above or below prior-defined drought trigger thresholds for select reservoirs within Texas. Such probabilistic information on reservoir storage could feed into a regional water planning group's drought management strategy, which is an interim strategy that the regions can adopt to meet near-term needs through demand reduction until long-term water supply measures are implemented.