The Influence of Remotely Sensed Leaf Area Index (LAI) on the Estimation of Evapotranspiration from SLURP Model

摘要

Evapotranspiration (ET) is an important state variable while simulating daily streamflow in hydrological models. In the estimation ofET, for example, when using FAO Penman Monteith equation, the LAI (Leaf Area Index) value reflecting the conditions ofvegetation generally affects considerably. Recently in evaluating the vegetation condition as a fixed quantity, the remotely sensed LAI from MODIS and NOAA satellite data is available, and the time series values of spatial LAI coupled with land use classes are utilized for ET evaluation. Four years (2001-2004) of MODIS LAI, MODIS NDVI and NOAA NDVI data were prepared for the evaluation ofETin the continuous hydrological model, SLURP (Semi-distributed Land Use-based Runoff Processes). The model was applied for simulating the dam inflow ofChungju watershed (6661.3 km~2) located in the upstream of Han river basin of South Korea. For 4 years (2001-2004) dam inflow data, the model was calibrated and verified using MODIS LAI data. The average Nash-Sutcliffemodel efficiency was 0.66. To identify the vegetation effect of two other cases (LAI from MODIS NDVI and LAI from NOAA NDVI), the model was run and the results were compared based on the MODIS LAI result. The model results showed that the watershed average AET under MODIS LAI condition was estimated 2.5 % and 1.0 % larger than the AETs by LAI from MODIS NDVI and LAI from NOAA NDVI respectively. Among the land uses, the AET for forests was highly affected by the different LAI application. Thus, it is necessary to collect the ground-measured LAI of forests with a more effort during the period of February to April or May. For the deciduous forest, additional careful LAI measurement during August to October or November is required.