Time-series analysis of evapotranspiration using normalized difference vegetation index over north-eastern and north-western agro-climatic zones of Tamil Nadu

Estimation of evapotranspiration spatially is mandatory for water budgeting and water resource monitoring based on crop water demand. The amount of evapotranspiration can be estimated spatially from reference evapotranspiration and fractional vegetation cover over the region. The incorporation of specific characteristics like spatial variability over the land cover produced highly reliable results. The AquaCrop model gives reference evapotranspiration based on climatic parameters like temperature, rainfall, solar radiation, relative humidity and elevation. Normalized Difference Vegetation Index (NDVI) depicts the health of vegetation spatially ranging from -1 to +1. The dimidiate pixel model converts NDVI to Fractional Vegetation Cover (FVC) which was then used as a substitute for crop coefficient value. The products of these two parameters produce actual evapotranspiration spatially over the region with high spatial resolution. The average amount of actual evapotranspiration varies for each Land Use Land Cover (LULC) type over different agroclimatic zones as the climatic parameters and water usage patterns vary for each land cover type.