All Dried Up? Modeling the Effects of Climate Change in California’s River Basins

Mono Lake
Whether you are trapped inside because of it, or mourning the lack of it, water is on everyone’s mind right now. Too much snow in the Midwest and Northeast has been ruining travel plans, while too little snow is limiting Californians’ annual ski trips. No one wants to drive three hours only to find a rocky hillside where their favorite slope used to be.

It’s hard to deny that abnormal things are happening with the weather right now. Recently, Governor Jerry Brown officially declared a state of emergency in California due to the drought and suggested that citizens cut water usage by 20%. With no relief in sight, it is important not only to regulate our current water use, but also to reevaluate our local programs and policies that will affect water usage in the future. So, how do we go about making these decisions without being able to predict what’s next? A recently published PLOS ONE article may offer an answer in the form of a model that allows us to estimate how potential future climate scenarios could affect our water supply.

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Researchers from UC Berkeley and the Stockholm Environmental Institute’s (SEI) office in Davis, CA built a hydrology simulation model of the Tuolumne and Merced River basins, both located in California’s Central Valley (pictured above). Their focus was on modeling the sensitivity of California’s water supply to possible increases in temperature. When building the model, the authors chose to incorporate historical water data, current water use regulations, and geographical information to estimate seasonal water availability across the Central Valley and the San Francisco Bay Area. They then ran various water availability scenarios through the model to predict how the region could be affected by rising temperatures.

Using estimated temperature increases of 2°C, 4°C, and 6°C, the model predicted earlier snowmelts, leading to a peak water flow earlier in the year than in previous years. The model also forecasted a decreased river flow due to increased evapotranspiration (temperature, humidity, and wind speed). The water supply was also estimated to drop incrementally with each temperature increase, though it is somewhat cushioned by the availability of water stored in California’s reservoirs.

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The authors used an existing model as an initial structure, and built upon it to include information on local land surface characteristics, evapotranspiration, precipitation, and runoff potential. Surrounding water districts were modeled as nodes and assigned a priority according to California’s established infrastructure and legislation. Using this information, the authors state that the tool is equipped to estimate monthly water allocation to agricultural and urban areas and compare it to historical averages for the same areas.

Though a broad model, the authors present it as a case study that provides estimates of longer-term water availability for the Central Valley and Bay Area, and encourage other areas to modify its design to meet the needs of their unique locales. Those of us looking for more specific predictions can also use the tool to create models with additional information and refined approximations, allowing flexibility for future changes in land use and policy. For now, we might have a good long-term view of our changing water supply and a vital tool as we race to keep up with our ever-changing world.

Citation: Kiparsky M, Joyce B, Purkey D, Young C (2014) Potential Impacts of Climate Warming on Water Supply Reliability in the Tuolumne and Merced River Basins, California. PLoS ONE 9(1): e84946. doi:10.1371/journal.pone.0084946

Image 1 Credit: Mono Lake by Stuart Rankin

Image 2 Credit: Figure 1 pone.0084946

Image 3 Credit: Figure 2 pone.0084946

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