Application of the Precipitation Runoff Modeling System to evaluate water budgets after forest fuel management

Abstract:

The Sagehen Experimental Forest is being used as a prototype for forest fuel management to mitigate severe wildfires and improve ecosystem function and habitat. Sagehen is located at the headwaters of Sagehen Creek and contributes to the Truckee River, which is the main water supply for Reno, Nevada. Sagehen is a snow-dominated basin that receives an average annual rainfall of 892 mm and streamflow of 392 mm. A standardized precipitation index (SPI) indicates eight wet years and three dry years occurred since 1978. The Precipitation Runoff Modeling System (PRMS) is utilized to run scenarios of fuel treatments and to analyze corresponding water budget changes in Sagehen. PRMS is calibrated to observed streamflow using the systematic multi-objective, step-wise calibration software Let Us Calibrate (LUCA). The basin is divided into 128 hydrologic response units (HRUs) based on similar hydrologic and physical characteristics. Fuel management will include multiple thinning and burning treatments based on topography and ecosystem characteristics and coincides with approximately 41 percent of the defined HRUs. Three treatment scenarios were run for relevant HRUs for water years 1981-2000. Scenarios reflect a 25, 50, and 75 percent vegetation reduction by altering sensitive parameters such as summer and winter cover density, summer and winter rain-interception storage capacity, and snow-interception storage capacity. Preliminary analysis shows changes in the water budget exemplified by simulated streamflow compared to baseline simulations. Ongoing work includes investigating PRMS outputs such as evapotranspiration, snow, and recharge to fully understand the scope of proposed fuel management in Sagehen. Individual assessment of impacted HRUs will also provide insight on specific treatment types and ultimately provide insight for future regional treatments in the Sierra Nevada.