Methodology of regional climate studies for West Texas and its importance
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As the recent droughts have highlighted, understanding the long-term effects of climate change on local water resources is critical for sound regional water planning. Appreciating the effects of climate change helps policy makers prioritize the mitigation/adaptation techniques to assure adequate water supplies in a time of uncertainty. Regional climate models that are focused on specific regions of interest are efficient tools that help policy makers incorporate climate change in their decision-making process. This report presents the findings of a regional climate impact study that was carried out for the Upper Brazos River basin in west Texas. The study area in the regional climate model was defined by performing model runs at Abilene, Amarillo, Baylor, Childress, Lubbock, and Midland National Weather Service climate stations. The PSU/NCAR mesoscale model MM5 was used to perform regional modeling. The analysis of the magnitude of hydrologic change for the study area is vital because 1. The Upper Brazos River is one of the main sources of water supply to the semi-arid lands in northwest Texas. 2. Water from some regions of the Upper Brazos River sub basin is infiltrating into the Ogallala aquifer, the major source of water supply for the High Plains of Texas. 3. The Upper Brazos River system is representative of West Texas water resources and can be applied to the region as a whole. 4. Little research of this kind was undertaken for the study area in past. A GCM that represents the climate forcings of the northwest Texas region efficiently was selected based on a careful comparison of the output from 15 GCMs. The comparison was based on two parameters, climate uncertainty and socio-economic uncertainty. IPCC scenarios A2 and B1 were chosen for this project as they represented the mid-high and mid-low climate change scenarios, respectively. The applicability of the regional model applied to the Upper Brazos River basin was validated by a 20-yr historical analysis (1970 - 1990) using reanalysis data. After validating the historical model, regional climate modeling was carried out for a period from 2030 to 2050 using CCSM GCM output. The hydrologic variables were analyzed and verified by comparing the model output from the historical runs with the climatic and meteorologic observations obtained from the NCDC and the TWDB. The results were analyzed to determine the key components impacting the hydrologic budget of the study area for historical and future time periods. Statistical analysis of long-term trends in precipitation and temperature components from model output were compared with observations for a historic period and projected for a future period. Trends in evaporation and in components affecting evaporation (wind and relative humidity) were studied. While the comparison of historical analysis verified the adaptability of the model, the future trends projected a decrease in the frequency and the magnitude of precipitation, increase in the temperature, relative humidity, and evaporation values in the Upper Brazos River basin. Further analysis of the future trends indicated increase in wind speed and increased scatter in wind direction. Therefore, it was concluded that a scientifically sound methodology to conduct regional climate modeling for the northwest Texas region was developed. The methodology used, the principles applied, and the results obtained were specific to the regional nature of study area. The sensitivity of regional climate was ascertained in every step of the research. The importance of hydrologic variables of the water cycle was analyzed and the trends of changes in these variables under changed climate conditions were studied.