Incorporation of Climate Change in Water Availability Modeling

The state of Texas recently implemented a water-availability modeling (WAM) system to support planning and regulatory activities. River basin hydrology is represented in the WAM system by sequences of historical monthly naturalized streamflows and net reservoir evaporation rates. This paper describes a case study investigation of the potential effects of climate-change on assessments of water-supply capabilities and focuses on whether and how climate change considerations should be incorporated in the WAM system. A modeling approach was adopted to explore the impacts of climate change on hydrologic and institutional water availability for the numerous water users who depend on supplies provided by the 118,000km2 Brazos River Basin. Analyses of historical naturalized streamflows indicate hidden but significant multiple-year cycles but no long-term trends during the twentieth century. A climate model and watershed hydrology model are used to adjust the WAM system hydrology to reflect anomalous climate during 2040–2060. The future climate scenario generally results in decreased mean streamflows and greater variability. However, the effects on water availability vary significantly in different regions of the river basin and among water users.