Assessing Future Changes of Climate Extremes in Supporting Regional Water Resource Planning over the South-Central United States

To improve resilience to climate extremes, regional decision makers need to know whether and how they will change in the next several decades based on climate model projections and decadal predictions. However, large uncertainties and disagreement between modeled and observed historical changes have largely prevented regional stakeholders from incorporating climate projections into their planning activities so far. To address this problem, we have evaluated uncertainties in the nine climate models that participated in the Inter-governmental Panel for Climate Change the Fifth Assessment (CMIP5). Most of these models realistically capture the general patterns of seasonal cycle, the probability distributions of rainrate and surface temperature, and the statistical distributions of the drought indices over the south-central United States (SC US). However, most models have wet and cold biases over this region. They underestimate the occurrence of T>90˚F and have large but inconsistent uncertainties in the occurrence of T>100˚F. These biases in most models are linked to the biases of the large-scale circulation that allows more frequent passages of synoptic disturbances during winter and spring and weakens the circulation pattern in favor of summer droughts. Likewise, the model that better captures the large-scale circulation pattern, the Pacific-North American wave-train patterns associated with El Niño-Southern Oscillation (ENSO), and the observed global SST warming mode and its relationship with an increase of summer rainfall over the SC US also has less biases in regional rainfall, surface temperature, drought. Thus, the “best performing model” appears to more realistically capture the key climate processes that control the SC US regional climate. Because the regional climate biases common in most of the models cannot be effectively reduced by their multi-model ensemble mean, we will show a comparison between the climate projections by the “best performing model” and those by the multi-model ensemble mean to assess the robustness of the climate projections and predictions for future drought and extreme temperatures over the SC US.