An ArcGIS toolbar was developed with the help of ArcObjects within ArcGIS environment to estimate evapotranspiration (ET) and net irrigation requirement (NIR) on raster based approach. The toolbar can estimate ET on a daily or monthly basis either with Hargreaves and Samani method or FAO56-PM method and calculate the corresponding NIR on a monthly basis. The toolbar was tested using normal monthly meteorological data (maximum temperature, minimum temperature, relative humidity, wind speed, solar radiation and rainfall) collected from 133 India Meteorological Department (IMD) stations covering 19 agro-ecological regions from 1971–2000. These point meteorological data were interpolated using ordinary kriging method and resampled at 1 km spatial resolution to generate the input rasters. Crop coefficient (k c ) raster for each month was prepared by analysing the cropping pattern of the country. Using the developed toolbar, reference evapotranspiration (ET o ) was estimated using both the methods on a monthly basis and NIR was estimated using the ET o of FAO56-PM method and comparison was made between the two ET o estimates. Verification of ET o and NIR estimates made by the toolbar was performed by comparing the toolbar estimated monthly ET o and NIR with manually calculated ones at ten evenly distributed locations and was found that the toolbar can generate accurate ET o and NIR rasters.
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