Change in Hydrologic Variables for Sierra Nevadas

This dataset includes Climatic Water Deficit (CWD) change, average winter (Dec, Jan, Feb) and average spring (Mar, Apr, May) snowpack change, recharge change, and runoff change from Basin Characterization Model (BCM) output using the GFDL and PCM A2 Scenarios in Sierra Nevada California, for 2010-2039, 2040-2069 and 2070-2099. The data was processed using historic (1979-2000) and future (2010-2039; 2040-2069; 2070-2099) values to calculate change. CWD: The term climatic water deficit defined by Stephenson (1998) is quantified as the amount of water by which potential evapotranspiration (PET) exceeds actual evapotranspiration (AET). This term effectively integrates the combined effects of solar radiation, evapotranspiration, and air temperature on watershed conditions given available soil moisture derived from precipitation. Climatic water deficit can be thought of as the amount of additional water that would have evaporated or transpired had it been present in the soils given the temperature forcing. This calculation is an estimate of drought stress on soils and plants and recent studies suggest it may serve as an effective control on vegetation cover types in the Bay Area (Cornwell 2010). In a Mediterranean climate, climatic water deficit can also be thought of as a surrogate for water demand based on irrigation needs, and changes in climatic water deficit effectively quantify the supplemental amount of water needed to maintain current vegetation cover, whether natural vegetation or agricultural crops. Climatic water deficit (CWD) quantifies evaporative demand exceeding available soil moisture, where S = soil moisture, AET = actual evapotranspiration, D =climatic water deficit. Snowpack: Amount of snow accumulated per month summed annually, or if divided by 12 average monthly snowpack. This is calculated as prior month's snowpack plus snowfall minus sublimation and snow melt. Recharge: Amount of water exceeding field capacity that enters bedrock, occurs at a rate determined by the hydraulic conductivity of the underlying materials, excess water (rejected recharge) is added to runoff. Runoff: Amount of water that becomes stream flow, summed annually. Modeled as amount of water that exceeds total soil storage and rejected recharge. The California Basin Characterization Model (BCM) climate dataset provides historical and projected climate surfaces for the state at a 270 meter resolution. The historical data is based on 4 kilometer PRISM data, and the projected climate surfaces are based on the A2 and B1 scenarios of the PCM and GFDL GCMs. The BCM approach uses a regional water balance model based on high resolution downscaled precipitation and temperature as well as elevation, geology, and soils to produce surfaces for a wide range of variables. These variables include maximum temperature, minimum temperature, precipitation, potential evapotranspiration, runoff, recharge, climatic water deficit, actual evapotranspiration, sublimation, soil water storage, snowfall, snowpack, snowmelt, and excess water. Data is distributed as 30-year monthly summaries and 30-year water year summaries, with month-by-month data for each year available by special request.