Estimation of Actual Evapotranspiration Using Satellite-Based Surface Energy Balance Derived from Landsat Imagery in Northern Thailand

In this study, satellite-based measures of surface energy balance and the mapping evapotranspiration at high resolution with internalized calibration (METRIC) from Landsat imagery were used to estimate the spatiotemporal distribution of actual evapotranspiration (ETa) in northern Thailand, constituting a procedure that has rarely been performed in southeast Asia. Subsequently, we compared the ETa obtained from METRIC with that calculated using the FAO-56 dual-crop coefficient method via the SIMDualKc software and found a strong correlation. An assessment of the accuracy of all the sample plots revealed the R-2, Root-Mean-Square Error (RMSE), and mean absolute error (MAE) values to be 0.830, 0.730, and 0.575 mm d(-1), respectively. Differences in the cumulative ETa values derived from SIMDualKc and METRIC ranged in magnitude from 0.93-3.57% for rice and 3.08-7.99% for longan. The ETa values for forestland and waterbodies were higher than those for agricultural areas and areas with other forms of land use. The spatiotemporal distribution of the seasonal ETa during the dry season was consistent with the climate, vegetation, and anthropogenic activity. Thus, our results indicate that METRIC is a reliable tool for estimating ETa for water resource management under different environmental conditions and improving water use efficiency over large areas.

Automated summary

In this study, satellite-based METRIC technique was used to estimate the spatiotemporal distribution of actual evapotranspiration (ETa) in northern Thailand, which has rarely been done in southeast Asia. The results showed a strong correlation between METRIC and FAO-56 dual-crop coefficient method. The study concludes that METRIC is a reliable tool for estimating ETa and improving water resource management efficiency over large areas.