PNNL

Abstract

Using a case study of the Yakima River Valley in Washington State, we show that relatively simple tools originally developed to forecast the impact of the El Niño phenomenon on water supplies to irrigated agriculture also can be used to estimate the significantly shifted probability distribution of water shortages in irrigated agriculture during climate change, and that these shifted probabilities can be used to estimate the impact on agriculture in a region. The more permanent nature of changes in the temperature and precipitation regime associated with climate change means that risk management options also take a more permanent form (such as changes in crops and cultivars, and adding storage). A number of storage options have been proposed to deal with El Niño-associated drought, and would be more valuable under climate change. The most ambitious of the proposed storage projects is Black Rock, which would add about 500,00 acre-feet of water to supplement the Yakima’s current 1.1 million acre-feet, at a cost currently estimated at $1.9 billion. For perspective, economic losses in the Yakima Valley reportedly have been about $100 million in a drought year such as 2001. Under current circumstances, the expected annual fisheries and periodic drought relief benefits may be large enough to justify the expenditure, but since drought has been occasional, environmental consequences of new projects uncertain, and the price tag beyond the reach of all but the Federal government, no projects have been built. The benefits become more certain with warming. Analysis shows that adding 500,000 acre-feet to TWSA would offset El Niño and the effects of 2º C warming.