The specific example of the 2011 Texas heat wave/drought illustrates the practical importance for understanding climate-extreme event relationships, The scientific undertaking reveals the need to reconcile previous regional climate trends, which did not show a long-term tendency toward increased heat or drought in the Texas region, with a heat wave event of record proportions. The assessment also illustrates the importance for considering multiple contributing factors, including human-induced climate change, effects of natural ocean variations and local land-atmosphere interactions, including the role of vegetation.

Previous studies identified an important role of land use changes on drought probabilities during the Dust Bowl period (Cook et al. 2009). What was the role of land surface changes, that evolved in concert with the 2011 record-setting Texas drought, leading to most intense heat wave in that region’s instrumental record? Are various impacts of physical processes associated with that drought, several of which were described in the paper currently under review by Hoerling et al. (2012), including antecedent and coincident soil moisture feedbacks, global climate change and greenhouse gas forcing, remote SST forcing from Pacific and Atlantic oceans, realistically modeled in current generation cliate and forecast models? What is the predictive understanding of the 2011 Texas heat wave/drought, as for example might be inferred from realtime forecasts, retrospective hindcasts, AMIP-style (in which ocean conditions are specified, not predicted) simulations, and uninitialized CMIP projections (in which greenhouse gas and aerosols alone are specified)?

There is a compelling public interest in understanding whether the heatwave/drought and other extremes of 2011 merely reflects variability of a chaotic climate system such that conditions should be expected to revert to climatological normals, or whether they more reflected regional manifestations of a changing climate such that they are harbingers of a new long-term regional climate trend. Addressing such questions poses many science challenges, but also outstanding opportunities. Because of the great diversity of phenomena, ranging from severe convective storms and hurricanes to sustained drought and heat waves, there is a need to consider numerous potential factors, anthropogenic and natural. Identifying systematic relationships also requires a much improved understanding of the connections between weather and climate. The potential payoffs to society from gains in this area are enormous, ranging from improved early warning of extreme events to providing information that is essential for longer-term adaptation decisions. Key to realizing those payoffs is understanding the sources of model uncertainties and evaluating the suitability of models in the representation of key physical processes, a major focus of this proposal.