HIGH DEMAND AND CLIMATE CHANGE: PROMINENT CHALLENGES FOR FUTURE WATER RESOURCES IN NORTH TEXAS

Water resources management in North Texas and surrounding regions faces a number of opportunities and challenges over the coming decades. As in many areas of the country, these are primarily a vexing combination of increasing demand and decreasing supply. Dallas Metroplex population is projected to increase by 2%/yr through 2050, with water demand increasing at a slightly lower rate. These rates may accelerate as growth slows in other areas of the nation. Per-capita water consumption in North Texas is the highest in the state for cities over 100,000 population, and approaches 300 gal/capita/day (GCPD). This offers clear opportunity for inaugural conservation efforts to have a significant impact on demand.

Simultaneously, the surface water resources that supply most of North Texas are likely to decline as a result of climate change. IPCC climate change models indicate an initial ~20-year period of slightly wetter conditions, which appears to have begun in the 1990's, (e.g. observed 1.5 inch increase in annual precipitation in the region vs. pre-1975 values). After 2020 predictions indicate minor drying accompanied by major warming. The net climate effect is readily illustrated by monthly Palmer Drought Severity Indices (PDSI) based on predicted temperature and precipitation. An ensemble mean of PDSI calculated from intermediate severity warming models (IPCC-SRESa1b) indicates initially wet conditions transitioning to permanent moderate drought after 2050. Values are: observed PDSI 1980-2000: +1.1, predicted 2000-2020: +0.26, 2040-2060: -0.57, 2080-2100: -1.4. Strong correlation of annual mean stream discharge with PDSI (Spearman rank indicates 99.9% confidence) allows prediction of future streamflow given PDSI. Doing this for streams supplying major reservoirs in North Texas indicates a climate-related decline in average streamflow of 30%-50% by 2050. Increased precipitation variability may allow reservoirs to moderate the short-term effects of such a decline, but in the long run, reliability of reservoirs may be threatened.