Satellite‐based regional‐scale evapotranspiration estimation mapping of the rice bowl of Tamil Nadu: A little water to spare^*

Abstract

Improved regular and rapid monitoring techniques are needed to quantify evapotranspiration (ET) precisely on agricultural fields to enhance the efficient usage of water resources and protect water quality and the environment. This study proposes estimating and mapping ET using a vegetation index coupled with a crop coefficient estimation method over the famous rice bowl region of Tamil Nadu, India. The study utilized a very high‐resolution satellite—Sentinel—of resolution 10 m. The study is based on a crop coefficient—Normalized Difference Vegetation Index (NDVI)—based ET estimation, which is one of the most adaptable practical approaches in quantifying crop water usage in multiple phases of crop growth on a regional scale. The results have been further calibrated using the surface energy‐based Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC) model to assess estimation correctness. The estimations analysed for the 2016–2019 kharif cropping season show good overall correlation with the coefficient of determination (R2) of ≥0.72, with mean bias error (MBE) of ≤0.0009 mm day−1 and root mean square error (RMSE) of ≤0.67 mm day−1, indicating a positive assessment of ET for the delta region of Tamil Nadu for reaching vindicable intendance of crop water in this region.

Terrestrial carbon cycle: tipping edge of climate change between the atmosphere and biosphere ecosystems

“…Studies suggest that the decadal increase of CO2 concentration enhanced the NPP availability by 20 -25% 10,153,157 . The increased CO2 concentration impacts the Chydrological cycle balance due to rapid photosynthesis, which decreases the evapotranspiration (ET) flux in the waterdeficient area 110,126,158 .…”

“…10,153,157 The increase in CO 2 concentration impacts the Chydrological cycle balance due to the rapid photosynthesis, which decreases the evapotranspiration (ET) ux in water-decient areas. 110,126,158 In another aspect, evapotranspiration (ET), which is an unavoidable component of the water cycle, is mediated by stomatal closure of the biota, corresponding to the efflux and inux of carbon through ER. 44,75,81 Under climate change, with the induced ET, the ecotypes in the terrestrial ecosystem experience soil drying with decreased soil-leaf water potential.…”

“…10,153,157 The increase in CO 2 concentration impacts the C-hydrological cycle balance due to the rapid photosynthesis, which decreases the evapotranspiration (ET) flux in water-deficient areas. 110,126,158…”