1. Real-time Sierra Nevada water monitoring system
Context & need
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.
Importance. Climate change introduces uncertainty into water forecasts that are based on historical statistical relationships, with errors greatest for conditions further from the historical mean. Increasing pressures on mountain water supplies & flood control also make accurate forecasting more important to water decision makers than in the past. 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 emerging as a critical response variable, which exhibits basin-scale variability with snow
Daily snow water equivalent estimates by elevation band (cumulative amount melted) for Tuolumne R. basin, 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.
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 accurate 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.
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 snow depth & soil moisture measurement nodes. On the order of 20 clusters will be deployed across a basin, taking advantage of existing snow & meteorological sites where possible.
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
DRAFT
DRAFT 1

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

3. Real-time Sierra Nevada water monitoring system
Use of proposed products in current & emerging decision support systems.
Use of snow products in existing decision support
Interpolated snow water equivalent from ground-based measurements, masked by satellite snow-covered area, gives 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 & by elevation band.
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..
Snow course
Snow pillow
Extended array
Typical layout for snow sensor & soil moisture array around a snow pillow & snow course site, Gin Flat, Yosemite NP.
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.
Snow depth sensor with radio
Installing soil moisture probes
DRAFT 3

4. Real-time Sierra Nevada water monitoring system
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.
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.
Management of forest & watershed resources
Real-time snow & soil moisture measurement system will also serve data that is useful for informing watershed management decisions.
Forest adaptive management is a major concern for protecting hydropower resources, returning forests to sustainable conditions, protecting habitat & water quality.
DRAFT 4