Tuesday, 15 January 2002: 8:45 AM
Evaluation of Alternative Potential Evapotranspiration Schemes for Use in National Weather Service River Forecast System
Potential evapotranspiration (PE) is one of the required input time series to run the rainfall-runoff models in National Weather Service River Forecast System (NWSRFS). There are many different methods to compute PE, depending on what type of hydrometeorologic forcing data is available. This presentation compares several PE schemes, including those used in current NWSRFS, NCEP LDAS NOAH land surface model, and VIC land surface model. All of these schemes are based on Penman's combination approach which considers both energy and aerodynamic limits on PE. The main difference between them are related to how solar incoming insolation is estimated. In current NWSRFS, a utility program called SYNTRAN which uses sky cover information is used to derive solar incoming insolation. NCEP LDAS NOAH scheme uses solar incoming insolation data derived from NESDIS satellite observations. The VIC scheme derives solar incoming insolation data based on daily maximum and minimum temperature, precipitation and average wind speed. This paper will examine the differences between these schemes by comparing PE computed during common data periods. The long term differences (annual and monthly total) as well as short term differences (diurnal variation pattern and daily total) will be analyzed. The differences due to variations in climatic regimes will be studied as well. This study is motivated by the fact that traditional method of collecting sky cover information is being phased out with the full implementation of Advance Surface Observation System (ASOS) in the US. The ultimate goal of this study is to upgrade the SYNTRAN program in NWSRFS with enhanced capabilities to ingest new sources and new type of hydrometeorologic data.