1. Bias in April 1 forecasts (underforecast) for July-April unimpaired runoff for 15 Sierra Nevada basins. 2005 was about 150% of average accumulation, i.e. a wet year. Real-time Sierra Nevada water monitoring system Context & need Importance. Increasing pressures on mountain water supplies & flood control make accurate forecasting more important to water decision makers now than in the past. Warming temperatures also introduce uncertainty into water forecasts that are based on historical statistical relationships, with errors greatest for conditions further from the historical mean. Accurate, real-time estimate of spatial snow amounts are critically needed & when available will provide an unprecedented, quantitative picture of snowcover across Sierra Nevada watersheds, which will inform water supply estimates, flood forecasts & resource management decisions. Soil moisture is a critical response variable, which exhibits basin-scale variability with snow. Conceptual design. A ground-based basin-scale design will consist of instrument clusters located along transects. The clusters will sample the main variables controlling snow distribution & melt, i.e. elevation, aspect, vegetation & in some cases, distance to a major ridge (wind effects). Each cluster will extend over 1-2 km distance, & include 10-20 snow depth & soil moisture measurement nodes. On the order of 20-30 clusters will be deployed across a basin, taking advantage of existing snow & meteorological sites where possible. Missing elements & enabling technology. The current ground-based measurement system for snow, designed for statistical water-supply seasonal forecasts, does not provide representative measurements of snow depth or water equivalent. A system of continuous representative measurements using low-cost technology, when blended with satellite snow-cover data, can provide an accurate, real-time estimate of spatial snow amounts. Three elements have recently come together that make deployment of a full-basin- scale measurement & information system feasible: i) accurate, sustained satellite estimates of snow covered area across mountain watersheds, ii) reliable, low-cost sensors & telemetry systems for snow and soil moisture, and iii) cyberinfrastructure advances to integrate data & deliver it in near real time. Expected outcomes. Deployment of a full-scale basin prototype will inform water management in that basin, serve as a testbed for deployment across the Sierra Nevada & provide data needed for research & development to modernize forecasting & decision-support systems. The resulting approach for estimating snowpack is robust relative to climate change, will improve forecast accuracy & will serve the state for decades to come. Daily snow water equivalent estimates by elevation band (cumulative amount melted) for Tuolumne R. basin, 2004. Upper panel is actual melt based on time series satellite snowcover & energy balance, estimated after snow has depleted. Lower panel simulates real-time forecast using existing, sparse snow telemetry data to estimate snow water equivalent across basin. Note errors in both timing & amount for lower panel, across all elevations. This is due to the relative lack of representative ground-based measurements. UC contacts: Roger Bales, Sierra Nevada Research Institute, UC Merced Jeff Dozier, Bren School, UC Santa Barbara Noah Molotch, School of Engineering, UC Los Angeles 1 H 2 O v2.0

2. Scenario for ground- based instrument deployment in American River basin, with existing instrumentation, land ownership & wilderness Real-time Sierra Nevada water monitoring system 2 Meteorological station Snow pillow Snow course Wilderness boundary New instrument cluster Basin boundary Highway USFS land 1-25 26-50 51-75 76-100 % SCA H 2 O v2.0

3. Snow course Snow pillow Extended array Use of proposed products in current & emerging decision support systems. Real-time Sierra Nevada water monitoring system Use of snow products in existing decision support Interpolated snow water equivalent from ground-based measurements, masked by satellite snow-covered area, gives a much more accurate estimate of snowpack water volume across a basin than does use of point snow pillow data alone. Snowpack estimates across a basin & by elevation band offer a quantitative measure of snowpack amount & seasonal runoff. Some water managers further evaluate these estimates by sub-basin & elevation band. 3 Use of snow products in emerging decision support Any one of several hydrologic models can be used to model snowmelt runoff, given spatial snow estimates plus spatial energy balance estimates. The project team will use PRMS, and make data available to other modeling teams Fraction of snowmelt coming from a given 300-m (1000 ft) elevation band, based on estimates of snow water equivalent distributed across Merced River basin. About one-third of the snowmelt comes from above 3000 m elevation, where there are no snow sites Snow depth sensor with radioInstalling soil moisture probes Typical layout for snow sensor & soil moisture array around a snow pillow & snow course site, Gin Flat, Yosemite NP. H 2 O v2.0

4. Broader watershed management issues & benefits of the proposed measurement & modeling system Links to flood forecasting NWS flood forecasting based largely on Quantitative Precipitation Forecast (QPF), e.g. from weather forecast model, plus relatively simple hydrologic model. Accurate snowpack estimates important for improving hydrologic modeling to accurately include rain on snow events & rapid snowmelt in hydrologic modeling. Soil moisture important variable in hydrologic models for flood forecasting. Management of forest & watershed resources Real-time snow & soil moisture measurement system will also serve data that is useful for informing watershed management decisions, e.g. fire, fuels, habitat, maintenance activities. Forest adaptive management is a major concern for protecting hydropower resources, returning forests to sustainable conditions, protecting habitat & water quality. Real-time Sierra Nevada water monitoring system 4 Links to NOAA research in American River NOAA’s Hydrometeorology Testbed (HMT) research program in the N. Fork, American River focuses largely on precipitation. Mainly deployment of instrumentation for measuring atmospheric water, with limited ground measurements of snow & soil moisture. Main satellite data used is for atmospheric moisture, e.g. off California coast. HMT will run through 2009 as a research project in N. Fork American River, with some instrumentation remaining on site for transition to operations. Good synergy with proposed satellite & ground-based monitoring system to provide more-complete, end-to- end hydrologic information. Could provide stimulus to extend instrumentation from N. Fork to entire basin. H 2 O v2.0