Evaluation of WAPOR for the Estimation of the Annual Rainfed Crops Biomass, Tunisia

In the Mediterranean region, considered as the prominent hotspot in future climate change projections, water scarcity becomes the main challenge for the agricultural sector. This is mainly the case of the Tunisian agriculture that is substantially based on rainfed crops to ensure food security. Thus, monitoring and assessing the vegetation conditions may provide accurate information, which allows improving water productivity and helps decision-making including water management. Currently, satellite-derived vegetation data has been widely used to assess the crop production and the effect of water shortage and extreme climatic events. In this context, the FAO portal to monitor water productivity through open-access of remotely sensed derived data (WaPOR) WAPOR database was developed to monitor the water productivity through remotely sensed derived data. The aim of this work is to evaluate WAPOR ability to estimate the biomass of rainfed annual crops in the Cap Bon region in the North-East of Tunisia. The WAPOR products covering the study area are available at the national level (Level 2) with a spatial resolution of 100 m. Measured aboveground of local cereals varieties of wheat, barley and oat and mixed fodder crops (faba-bean, triticale and vetch) was compared to the estimated actual evapotranspiration and interception (ETa_WAPOR), during four years with different climatic conditions. The area of the considered agricultural fields varies from less than one hectare to around 10 ha. The estimated cumulative actual evapotranspiration (ETa_WAPOR) calculated from the predicted decadal ETa shows an acceptable correlation with the monitored dry biomass (R² = 0.78) but with high RMSE value of around 2.7 ton/ha. The performance of WAPOR estimation doesn’t seem to vary with seasonal climatic conditions.