STUDY ON EVAPOTRANSPIRATION FROM CATCHMENTS UNDER A DRY METEOROLOGICAL CONDITION

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In this project, properties of evapotranspiration from catchments were studied using the hydrologic data, which were collected in various catchments in Japan and middle America, to investigate the effects of wetness and vegetation on the eapotranspiration.Water valance method was applied to know the annual evapotranspiration from the catchments and ratio of the evapotranspiration to potential evaporation, I.e. evapotranspiration ratio, were compared among the catchments to be discuss. The results showed that the annual ratio depends on the annual precipitation and land use, or condition of the vegetation. In the catchments with poor vegetation, the ratio was relatively less and was more greatly affected by wetness.Data of satellite (Landsat) were analyzed to identify the properties of vegetation in each catchment. As a result, it was found that the data and analysis were very available to quantify the activity of vegetation and a relationship with high correlation was recognized between Normalized Difference Vegetation Index (NDVI) and the evaporation ratio.A new hydrologic model was developed to investigate properties of the evapotranspiration in more detail. The model was applied to some of the catchments and the important results were obtained on the properties.