1. Catchment Scale Streamflow Response to Climate Variability in the Rain-Snow Transition Zone of California's Sierra Nevada Mountains T.C. Harmon [1,2] and S.M. Jepsen [1] [1] Sierra Nevada Research Institute, University of California Merced, USA [2] School of Engineering, University of California Merced, USA CZO Annual Meeting, 20 August 2013

2. NSF WSC Project Aims/Methods WSC project extends from headwaters to the San Joaquin Valley floor (here, focus is on headwaters) Integrated watershed model: PIHM (Penn State) Tightly coupled surface water- groundwater interactions Goal: Characterize catchment response to spatiotemporal changes in rainfall and snowmelt Shaver Lake Providence sub-catchments Study Area - Providence 5 km

3. Recent Results/Findings Adjustments made to hydrologic model (PIHM) to simulate desired snowmelt dynamics Preliminary model results show stream discharge too late in year Need earlier modeled runoff Ideas to test in model: – Increase hydraulic conductivity? – Simulate horizontal macropores? – Decrease snowfall:rainfall ratio? – Nonuniform soil and snow depths? Upper Providence sub-catchment, water year 2006 Stream discharge (10 4 m 3 /day) Day of water year 2006 SWE (m)

4. Proposed Aims/Methods for Improved Model Output Finalize model calibration protocols leveraging computational cluster – Compare outcomes with RHESSys? Analyze sensitivity of flow paths (overland, groundwater) to soil parameters and model forcings Explore idea of adding spatially distributed snowmelt: – Available input: snow pillows, pingers, and lidar products – Incorporate separate snowmelt model? (e.g., ISNOBAL) Param 1Param 2Param 3… Run 1 values … Run 2 values … Incorporate interface to facilitate model calibration, e.g.:......