Using Sentinel-2 and weather data is possible to calculate the evapotranspiration and its excess or deficit. Here you have an example of use Article Capability of Sentinel-2 data for estimating maximum evapotr...

Dear Kul Khand , the crop water stress can be characterized using moisture indicators deriverd from IR thermal RS data, such as evaporative fraction, Bowen ratio, the Priestley-Taylor parameter and surface resistance to evaporation. These indicators are calculated from the resolution of the surface energy balance equation using different Energy Balance remotely sensed models, such as, SEBAL, METRIC, trapezoid model, SEBS, S-SEBI, TSEB, etc.

Regards

Thank you Juan Pedro Carbonell-Rivera for sharing the paper.

Dear HAMIMED Abderrahmane , thank you for your insight. Would you please be specific considering any of these surface energy balance models..

Very interesting

I would suggest the METRIC surface energy balance algorithm. Rather complicated although to calibrate manually. If you're familiar with R, a package has been coded to bypass the complexities.

“Allen, R.G., B. Burnett, W. Kramber, J. Huntington, J. Kjaersgaard, et al. 2013. Automated Calibration of the METRIC-Landsat Evapotranspiration Process. J Am Water Resour Assoc 49(3): 563–576. doi: 10.1111/jawr.12056.”

https://cran.r-project.org/web/packages/water/vignettes/METRIC_simple.html

Thanks Meyer Bohn , any thoughts on how METRIC handles the impact of excess water stress on ET?

METRIC calculates ET as a relative measure (ETrF) or the evaporative fraction of a reference crop (ETr) in which they use a "fully-transpiring alfalfa". The alfalfa unit is arbitrary, but what is powerful about it is that it allows you to internally calibrate across your study area. The low ET pixel anchor is "bare, dry soil" (from SAVI) and the wet pixel anchor is the ETr. I would run a regression between crop NDVI or SAVI values and ETrF to determine correlation. Although SAVI is included in the METRIC calculation (which breaks the assumption that variables in regression shouldn't be multicollinear) I think its worth a shot. In digital soil mapping, we break that assumption all the time because in reality these relationships aren't linear.

Dear Kul Khand

I agree with the colleagues by proposing METRIC as an approach well suited for monitoring the state of crop water stress. But, there are also other models such as the trapezoid and S-SEBI methods which are very simple and easily programmable.

Thanks much Meyer Bohn and HAMIMED Abderrahmane for your inputs. Looks like the comparison between VIs (NDVI, SAVI, NDWI) and ETrF maps is one of the ways to evaluate the impact of excess water on ET using remote sensing. Usually, this situation is uncommon during peak growing season for summer crops but may occur in areas with shallow groundwater and limited drainage.

Yes it's a good idea to compare Vegetation Index with Evaporative Fraction for evaluating the impact of excess water on evapotranspiration flux.

Here is the link of the SEBAL model source code by means GRASS and PYTHON:

https://zenodo.org/record/1303413#.XBPP7NTMet8

https://zenodo.org/record/1303413/files/SEBAL_v10.py?download=1

Regards

Thank you HAMIMED Abderrahmane .

You can use Tri-Angle or trapezoid method, the attached links may be help.

Article Estimation of Regional Evapotranspiration Based on Tri-Angle...

Article Assessment of the mutual impact between climate and vegetati...

I think stress due to water shortage is probably more common in remote sensing based ET models than due to the excess water. Majority of ET models (such as BAITSSS) assume excess water i.e. above field capacity is either deep percolated or runoff. So, having excess water goes to another level question to plant biophysical properties and aeration. I think, basically, the majority of ET models are utilized to understand plant stress due to water shortage (BAITSSS) than excess water.

Please visit.

BAITSSS utilize Javis type canopy resistance computation to understand the possile water stress due to water shortage.

https://sites.google.com/site/dhun9265/BAITSSS

https://www.researchgate.net/publication/328829421_Next_Generation_Landscape_Evapotranspiration_Tools_Is_It_Feasible

Dear Ramesh Dhungel , Thanks for your inputs and sharing the links.

Hello. consider the SAGA GIS software. ill draining areas can be demarcated using DEM derived topographical wetness index (TWI), closed depressions (CD) and flow accumulation (FA) parameters. All these parameters can be derived with SAGA.

Thanks Juan Pedro Carbonell-Rivera

Dear Farnando, thanks for sharing the paper.