Specific Objectives of the Project:
The objective of this proposal is to isolate the effect of droughts and heat on access to drinking water and drinking water quality in rural agricultural communities in the San Joaquin Valley.

Summary of Results:
A first preliminary result indicates that farmers are responding to heat and surface water scarcity through the construction of groundwater wells. We estimate that for each acre foot (AF) of reduced surface water allocations for agriculture, the annual rate of agricultural well construction increases by 46%. Using an approximated cost of $75,000 to construct an agricultural well, this translates to a back-of-the-envelope $37 million dollars invested annually in extensive-margin adaptation behavior by California farmers. Our finding that extreme heat will increase groundwater extraction brings a new data point to our understanding of how climate change will influence water resources. Our results highlight that even if water supplies remain unchanged, warmer temperatures will increase demand for groundwater, with an additional harmful degree day increasing well construction by 1.2%.

A second set of preliminary results indicates that extreme heat and reductions in agricultural surface water supplies lower the depth to the groundwater table. A 1-AF of reduced agricultural surface water allocation to every California cropland acre, lowers local groundwater levels by an additional 4 feet. An additional harmful degree day reduces groundwater levels by 0.5 inches. Declining water tables suggest that the costs of climate change may be larger in the long-run if farmers cannot avail themselves on groundwater resources.

Extreme heat and surface water scarcity also lead to domestic well failures, with a 1 AF decrease in surface water supplies and an extra HDD increasing failures by 5 and 0.2 percentage points, respectively. These results are consistent with a theoretical framework and computational hydrology model in which increased groundwater consumption among agricultural users comes at the cost of drinking water supplies through the channel of a declining water table.