PAYING TO IGNORE CLIMATE CHANGE? CHRONIC DROUGHT VS. WATER CONTRACTS IN NORTH TEXAS

Chronic low-level drought in North Texas (NTX) has kept reservoirs low, reaching trigger levels for mandatory conservation 31% of days since 2000 for the North Texas Municipal Water District (NTMWD). “Take-or-pay” water delivery contracts between NTMWD and 13 NTX cities require advance purchase of water equal to the maximum historical annual consumption. Since 2000, the 13 cities contracted with NTMWD have used 10-20% less than their historical maximum annually, and for FY 2013-14 these cities paid for an average of 21% more water than they consumed (after rebate). This serves as a strong disincentive for voluntary water conservation, and will eventually have to be addressed if current climate trends continue.

NTX depends almost exclusively on surface water, and runoff has declined 20% from its peak in the 1990’s. During that time, Palmer Drought Severity Index has trended negative, while precipitation has remained above normal, indicating that increasing temperature is the main driver of runoff declines. Analysis of historic runoff elasticity shows NTX runoff is unusually sensitive to climate variation, likely a consequence of its extensive cracking soils. Models of future climate for NTX predict continued average or above precipitation, and steady warming, with moderate to large reductions in runoff. An average of 30 downscaled CMIP5-VIC models suggests a 5-10% decline in runoff by 2050. More sensitive locally-calibrated runoff models using CMIP5-projected climate with the Texas Water Rights Analysis Package (WRAP, with future runoff elasticity similar to historical) indicate an average 18% decline in runoff by 2030 and 28% by 2050.

Unanticipated persistent water shortages are costing taxpayers directly in NTX, and most climate projections indicate future water supply will continue to be affected by declining runoff. This trend is not considered in current drought plans or delivery contracts. Short term adaptation to these trends in average water availability will require NTMWD client cities to continue to budget for undelivered water, and may drive reconsideration of take-or-pay contract structures. Long term adaptation will require modification of current water importation, storage and conservation/reuse plans.