Climate Change Impacts on Forecast Informed Reservoir Operations (FIRO) for Lake Mendocino in the Russian River Valley of California.”

Abstract:

An analysis of the climate change literature and reservoir operation modeling is performed to evaluate potential impacts of climate change on the operation of the Army Corps of Engineer’s Lake Mendocino in Mendocino County, California. Precipitation changed projected for California under climate change scenarios vary quite a bit, but the overall consensus is that by the year 2100 in Northern California, there might be a 10% increase in wet season precipitation (November to April) and a 1% decrease in dry season precipitation (May-October). Operation of Lake Mendocino has joint flood risk, water supply, and ecological flow requirements.

In the Russian River Basin, a multi-agency effort termed the Forecast-Informed Reservoir Operations (FIRO) study has been underway to assess the potential for both improved streamflow predictions and upgraded (forecast-informed) reservoir operating rules to make water management more efficient in the face of extreme weather and climate events that typically lead to flooding or drought. As part of the FIRO effort a network of surface meteorological, soil moisture, and stream gauges in the Potter Valley portion of the upper Russian River was installed and measured to aid in model calibration. The fully calibrated Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model simulates primarily overland flow and discharge of groundwater. From the calibrated GSSHA watershed model output a runoff coefficient (total runoff/total precipitation) of 0.50 is calculated. This value is used to adjust the projected flows from the Basin Characterization Model (BCM) providing the streamflow into the Lake Mendocino used as forcings by the ResSIM model. These flows are increased +10% for wet periods, and decreased by -1% for dry periods and then reduced by Runoff Coefficient of 0.50, resulting in a net increase for wet periods of +5% (+0.05) and -1% (0.005) . The Corps of Engineers ResSIM model is then run for the operations periods for management of the lake of 1910 to 2013 with these changes in the flow compared to the base case (current configuration). The change in lake storage resulting from climate change is minor.