Improving water resources management in the western United States through use of Improving water resources management in the western United States through use of remote sensing data and seasonal climate forecasts remote sensing data and seasonal climate forecasts

Eric Rosenberg1, Andrew Wood1, Qiuhong Tang1, Anne Steinemann1, Bisher Imam2, Soroosh Sorooshian2, and Dennis Lettenmaier1

1Department of Civil and Environmental Engineering, University of Washington, Seattle, WA 98195 2Department of Civil and Environmental Engineering, UC Irvine, Irvine, CA 92697

Project Overview

Models and data resulting from NASA and NOAA research have the potential to improve water management, but there are few concrete examples where advanced hydrologic modeling and remote sensing data have been used in the water management decision process. This study attempts to address this problem in the context of two western United States case studies – the Klamath River basin of Oregon and the Sacramento River basin of California. NASA and NOAA research results of three types are being investigated for adaptation and use by water management agencies:

Earth Observing System MODIS products, including those that characterize snow cover extent, evapotranspiration (from which crop water use is estimated), and reservoir surface temperature (a key variable for estimation of reservoir evaporation), and AMSR-E snow water equivalent tools, and

NASA’s experimental seasonal climate forecasts, which are produced by the GMAO model and already utilized in UW’s west-wide seasonal hydrologic forecast system.

Seasonal climate outlooks from NOAA’s CPC

Research is being conducted in partnership with three operational water management agencies:

USDA Natural Resources Conservation Service, which provides seasonal streamflow forecasts over most of the west,

US Bureau of Reclamation, which has authority within the Klamath River basin, and

California Department of Water Resources (DWR), which has authority for much of the Sacramento River basin.

A retrospective assessment is currently underway to evaluate the skill of CPC seasonal outlooks in the study areas. DWR has also expressed the following perspectives on the potential of NASA’s products:

The MODIS snow cover extent product could be useful as a check against measured snowpack depths.

The MODIS crop-water use product could be valuable for estimating accretions to the river systems for flow into the Delta.

General potential exists for using seasonal climate forecasts to resolve disparities between flood control forecasts, which are based on meteorological forecasts, and water supply forecasts, which are based on historical climatology.

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STORAGE INFLOW OUTFLOW

Contractors make initial requests

Forecast System Implementation

The Feather River watershed against VIC’s 1/8° grid cells.

Implementation of the UW west-wide forecast system has begun with the Klamath River and the Feather River, a major tributary of the Sacramento River. Watersheds were delineated against the Variable Infiltration Capacity (VIC) hydrologic model's 1/8 degree grid cells (Liang et al., 1994; Cherkauer et al., 2003), and are currently being upgraded to a 1/16 degree resolution. Real-time implementation is proceeding with the nowcast mode before progressing to the forecast mode (without MODIS snow inputs), and finally, the forecast mode with MODIS snow inputs. Examples shown are from a retrospective assessment.

VIC Snow CoverJanuary 11, 2004

1. Streamflow for the Feather River at Oroville Reservoir was simulated using the VIC, applied at daily time step (hourly for the embedded snow accumulation and ablation model).

2. Retrospective Ensemble Streamflow Prediction (ESP) forecasts of April-July streamflow were initiated on the first day of January, February, March, April, May and June. The black dots are ensemble member values, the green circles are ensemble averages, and the red bars are observations.

3. Scatterplots of hindcast ensemble means and observations were generated, showing the increase in correlation from January through June as forecast lead time decreases.

4. Although hindcasts showed adequate correlations with observations, the uncertainty bounds provided by the ESP forecast technique were erroneously narrow, suggesting forecast overconfidence. As a result, a forecast calibration approach was explored that corrected for forecast uncertainty errors, based on using the ESP mean as a single value forecast and formulating the uncertainty from both correlation and climatological information. The resulting forecasts (green symbols) matched those observed during the 56-year hindcast evaluation period.

5. The raw ESP ensembles showed increasing overconfidence and undersimulated dispersion, as well as bias, as the forecast season progressed. The calibration approach restored the uncertainty to the forecast ensembles, so that the observed and forecast frequencies (blue) fell close to a 1:1 line on the reliability diagram.

A retrospective assessment of forecast system performance was conducted in the Feather River watershed to serve as the basis for evaluation and modification of the forecast system. Although hindcasts showed adequate correlations with observations, the uncertainty bounds provided by the ESP forecast technique were erroneously narrow, suggesting forecast overconfidence. As a result, a calibration approach was developed that corrected for forecast uncertainty errors (Wood, 2007).

Retrospective Assessment Decision Support

The Terra satellite (top), the first to carry the MODIS sensor, was launched in Dec 1999. The Aqua satellite (middle), the second to carry the MODIS sensor, was launched in May 2002. The study areas for the project (bottom) are the Klamath R. basin of Oregon and the Sacramento R. basin of California.

Acknowledgements

References

Funding has been provided by NASA’s Water Management Program and NOAA.

Cherkauer, K.A., L.C. Bowling, and D.P. Lettenmaier. 2003. Variable Infiltration Capacity (VIC) cold land process model updates, Global and Planetary Change 38, 151-159.

Liang, X., D.P. Lettenmaier, E.F. Wood, and S.J. Burges. 1994. A simple hydrologically based model of land surface water and energy fluxes for general circulation models, J. of Geophysical Research 99, 14415-14428.

Ray, A.J. and R.S. Webb. 2000. Demand-side perspective on climate services for reservoir management, Proceedings of the Climate Diagnostics and Prediction Workshop, Palisades, NY, 23-27 October 2000, 219-222.

Wood, A.W. 2007. Correcting errors in streamflow forecast ensemble mean and spread, J. of Hydrometeorology (in review).

Opportunities exist to improve DWR’s seasonal forecasts through the use of climate and remote sensing information. Current forecasts employ statistical methods and are based on an 80-year climatology (soon to be changed to a 50-year climatology). These forecasts generally do not incorporate climate trends (e.g., observed warming in the recent past) or climate variability (e.g., ENSO and PDO signals).

The following decision calendar (adapted from Ray and Webb, 2000) illustrates DWR’s current forecasting and allocation schedule against Oroville Reservoir’s operations for 2002-2003. Initial water allocations for the coming calendar year are made by DWR in December. The longer lead times offered by climate-based forecasts could result in considerable improvements to system performance.

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Allocations approved and revised by DWR

Monthly snow surveys conducted

Official forecasts issued for April-July runoff

Ongoing Activities

ENSO forecast typically available for coming winter

The Feather River watershed against VIC’s 1/16° grid cells.

MODIS Snow CoverJanuary 11, 2004