On the twenty-first-century wet season projections over the Southeastern United States
We have focused our study of regional climate change on a single variable, precipitation, which we believe is an integrated quantity that reflects important aspects of the total atmospheric response. We discuss the results of regional climate change over the SEUS from one global model (CCSM3 at *150-km grid resolution) and its dynamically downscaled climate at 10-km grid resolution using the RSM. This study emphasizes on the understanding of the physical mechanisms that produce the model projections more than the absolute magnitude of anticipated changes.
The results of our study, consistent with the results of earlier studies on the subject, show that CCSM3 displays a dipole-like change in the mean summer precipitation for the A2 emission scenario: Peninsular Florida and adjacent oceans dry, and the remainder of the SEUS becomes wetter relative to the corresponding mean summer rainfall of the late-twentieth-century simulation. In the dynamically downscaled simulation using the RSM, the summer precipitation response is different in that it shows a uniform drying across the SEUS. We trace the differences between these model projections to the RSM displaying a reasonable fidelity in depicting the diurnal variations in the summer climate in SEUS. This is in contrast to CCSM3, which displays a poor fidelity of diurnal variations. The RSM indicates a significant reduction in the rainfall during the time of diurnal peak in the late twenty-first century. This reduction in the diurnal maximum rainfall in RSM is in response to large-scale changes in the westward shift of the NASH and the relative warming of the tropospheric temperature resulting from warm SST anomalies in the equatorial Pacific Ocean.
The results we present are of concern to the agriculture industry of the SEUS. In the SEUS agriculture is primarily rain fed (Misra et al. 2011a, b), making it particularly sensitive to rainfall variability. Observations indicate that because of the summer season rainfall, the SEUS is climatologically the wettest region in the conterminous United States (Chan and Misra 2010). Sustaining the multibillion-dollar agriculture industry (Hansen et al. 1998), forecasted to grow in the coming years, imparts an urgency to understanding rainfall changes arising from climate change, especially during the summer growing season over the SEUS. The booming population of the region (Seager et al. 2009) and the ability to meet growing demands for freshwater while simultaneously preventing saltwater intrusion into the aquifers (Karl et al. 2009) are also major concerns in managing water resources. Further studies such as this one are required in order to create a robust collection of outcomes for decision-makers.
We acknowledge the editorial assistance of Kathy Fearon of COAPS, FSU. This study was supported by grants from NOAA (NA07OAR4310221), USDA (027865), and USGS (06HQGR0125).