Abstract
Evapotranspiration (ET) is one of the major elements in the water circulating process on the earth. From the view point of water resources or water utilization, the distribution of ET over wide area in a long term, like monthly, should be considered in connection with the regional characteristics of topography or landuse. Remote sensing technique is a probable means to estimate the distribution of ET over wide area, however this technique has some difficulties to measure ET directly for a long duration.
Here the model which adopts an indirect method to estimate ET has been developed by using Landsat MSS, digitized elevation and observed meteorologi-cal data near the ground. In order to examine the effects of topography or landuse conditions on the amount of ET, some calculating experiments have been executed by this model, which is able to estimate ET under arbitrary presumed conditions. The results of calculation are summarized in the following.
With regard to the topographic conditions, the amount of ET is scarecely affected by the variance of elevation unless the area has dominant slope orientation. On the other hand the value of elevation averaged in the area is found to be a significant indicator of topographic conditions on ET.
Landuse conditions are represented by reducing to two empirical parameters in the model. The regional averaged values of these parameters might be choosen as representative indicators of landuse in wide area relating to the environmental condition on ET. This result suggests that there is a possibil-lity to trace the landuse change in the past and to assess the conversion in the future from the hydrological point of view by adopting remote sens-ing technique.
