The Ratio Distribution of Evapotranspiration to Precipitation well Related With Soil Thickness in Karst Watershed of Southwest China

Abstract

AbstractEvapotranspiration (ET) is predominant variable for water management in various types of ecosystems, and it has been intensively studied through in situ measuring and modeling methods. However, it is challenging to measure actual ET and upscale it to regional level for karst landscapes, where aquifers typically show remarkable and rapid responses to precipitation events. There is an urgent need to quantify water fluxes to provide reliable evidence for the protection and sustainable management of karst water resources. Therefore, in this study, five plots were built to observe actual ET based on Thermal Dissipation Probes, redesigned ventilated chamber and in‐site microlysimeters in a karst watershed in southwest China. Then, three models (Penman‐Monteith‐Leurning, PML; Remote Sensing‐Priestley and Taylor; and Hargreaves) were constructed to upscale ET estimation to the regional level based on Landsat‐8 images and MODIS data. The results showed that: (a) The PML model performed better than other models (p < 0.01) with higher R2 values (0.72 for MODIS images and 0.87 for Landsat‐8 images); (b) Daily ET exhibited significant seasonal variability and different spatial distribution, and yearly ET exhibited well related with soil thickness (R2 = 0.58); (c) Daily ET had a slightly positive correlation with DEM, however, had a negative correlation with ground temperature. This study is helpful to improve accuracy of measured and estimated ET by combining remote sensing data, and it has important implications for upscaling it to regional level. It suggests that ET is strongly regulated by constant supply of water, vegetation coverage, and available energy in karst catchments.