Irrigation Water Retrieval Through Data Assimilation of Surface Soil Moisture into the FAO-56 Approach in the South Mediterranean Region

Optimizing irrigation (timing and amount) is a worldwide requirement for water resource management, especially in semi-arid regions suffering already from limited water supply. In this study, an approach for estimating daily to seasonal irrigation amount is developed. The approach assimilates the surface soil moisture (SSM) estimated from Sentinel-1 radar data using a particle filter algorithm into the FAO-56 double coefficient model. The approach is tested over a drip irrigated wheat field located in the center of Morocco during two successive growing seasons. It is evaluated using in situ SSM measurements and using Sentinel-1 SSM products. Assimilation of Sentinel-1 SSM products, available every 6 days, yielded accurate irrigation estimates. The seasonal amounts are estimated with a maximum difference of 28 mm (8%) and 15-days cumulative irrigation amounts are reasonable with R=0.64, RMSE=28.78 mm and bias=1.99 mm.