ASSESSMENT OF LONG-TERM DROUGHT CHARACTERISTICS IN 14 MAJOR TEXAS CITIES BASED ON CMIP5 MULTI-MODEL PROJECTIONS

Abstract:

Texas is a highly water-stressed region due to rapid population growth and frequent droughts. Characterizing long-term drought is thus critical for sustainable water use planning. The Standardised Precipitation Evaporation Index (SPEI) is a widely-used drought index as it considers both the supply and demand elements of the water balance and can be used to compare drought characteristics across locations. In this study, bias-corrected and spatially disaggregated (BCSD) temperature and precipitation projections from an ensemble of Coupled Model Intercomparison Project 5 (CMIP5) earth system models were used to develop the SPEI for 14 major cities spread across different climate divisions of Texas. The SPEI were computed for 12 and 24 month scales for the Representative Concentration Pathway (RCP) 8.5 scenario for three time periods, 1950-1999 (historic), 2000-2049 (early), and 2050-2099 (latter). Both the SPEI-12 and SPEI-24 show a sharply-declining trend beginning in middle of the 21^st century across all locations. The most severe droughts, characterized by the number of consecutive and overall months with SPEI ≤ 1.5, generally occur in the last two decades of the 21^st century, particularly in semi-arid locations like El Paso and Laredo and appear to be controlled by potential evapotranspiration (PET). In addition, decreasing trends are observed in annual precipitation in major urban areas such as Austin, San Antonio and Houston. The results of the study highlight the need for proper management of water resources to match the trends in climate, economic and demographic changes.