Earlier this week, the Department of Interior released a report describing the projected shifts in temperature, precipitation and runoff caused by climate change in eight Western river basins.

Three of the eight river basins are of importance for California agriculture, most notably the Sacramento and San Joaquin basins that provide water for six of the state’s top 10 agricultural counties. The report also looked at the Klamath basin (in northern California) and the Colorado basin (supplying the agriculturally important Imperial Valley).

Fact sheets and the full report provide detail, but generally the report validates what other analyses have found—that California’s water supplies will be greatly stressed by reduced snowpack and changed patterns of runoff, and existing tensions between agricultural, urban and environmental uses of the water will exacerbate.

In a nutshell, this is how it will happen. In this century, temperatures will increase by roughly 5-6 °F in each of the river systems. The warmer conditions will cause earlier snowmelt and more moisture falling as rain instead of snow at lower elevations, thereby increasing the risk of flooding. Because late spring and summer runoff will decrease, there will be greater surface water shortages through the summer dry season, significantly increasing future demands on groundwater. Particularly in the Colorado system, warming will also cause significant reservoir evaporation and losses during water conveyance and irrigation. The warmer temperatures will cause increased water demands by agriculture at times when less water will be available.

Warmer conditions might result in increased fishery stress, reduced salmon habitat, increased water demands for instream ecosystems, shifts in species geographic ranges, and increased invasive species infestations. Endangered species issues might be exacerbated.

Warmer temperatures will increase the demand for electricity—especially during hot summer months—while at the same time the reduced water supply will hamper hydropower generation. This will put pressure on both the demand and cost of electricity.

This report paints an obviously bleak picture for agriculture. Combined with other expected impacts—new pest, invasive species and disease pressures, decreased chill hours essential for fruit and nut production, livestock stress, and erratic and extreme weather events—the notorious adaptability of farmers and ranchers will be put to the test and the principles and practices of sustainable agriculture will no longer be a philosophical or market-based choice but rather an imperative for survival.