Hydrology and Water Resources: Current Research
UW Westwide Hydrologic Forecast System and Surface Water Monitor
- Dennis Lettenmaier, UW Climate Impacts Group
Over the last decade, great strides have been made in land surface modeling at regional to continental scales. The North American Land Data Assimilation System (NLDAS) has developed new approaches for estimating current land surface moisture conditions (e.g., soil moisture, snow and runoff) as well as retrospective reconstructions of the same variables. These science-based products were motivated by a need to improve initialization of numerical weather prediction models, but have many other potential applications both in research and operations.
The University of Washington's Westwide Hydrologic Forecast System and Surface Water Monitor (SWM) meld these advances into a system that serves both hydrologic forecast and drought management objectives. Both the SWM and the Westwide Forecast System are continental U.S. implementations of NLDAS models that combine retrospective daily analysis of over 90 years with real-time, daily-updating simulations of land surface climate and moisture conditions. The retrospective dataset provides a foundation for research toward understanding hydrologic trends and variability on a national scale since 1915. It also provides an unusually consistent statistical background for interpreting the real-time moisture estimates, enabling their depiction as anomalies or percentiles with respect to historical conditions. The real-time percentile maps and predictions have already become an input to national-scale operational drought management efforts such as the US Drought Monitor and the Climate Prediction Center Drought Outlook. The system is also used for prediction at seasonal lead times, enabling the production of operational hydrologic, drought-oriented forecasts that complement those currently available from operational centers.
The SWM produces nowcasts of soil moisture and runoff conditions over the U.S. and Mexico at one-half degree spatial resolution, which are updated daily for four NLDAS land surface models, and for a multimodel composite. The higher resolution Westwide Forecast System operates at a higher one-eighth degree spatial resolution, for one model (Variable Infiltration Capacity, or VIC) only, but also includes several seasonal (six months to one year lead) forecasts of soil moisture and other land surface variables, as well as streamflow at approximately 200 forecast points.
Climate Prediction Center
For publications on climate impacts on PNW water resources, please see CIG Publications.
Wang A., T.J. Bohn, S.P. Mahanama, R.D. Koster, and D.P. Lettenmaier. 2009. Multimodel ensemble reconstruction of drought over the continental United States. Journal of Climate 22(10): 2694–2712.