A modified METRIC model for high resolution partitioning and mapping of evapotranspiration over irrigated agricultural landscapes in Morocco

Partitioning of evapotranspiration (ET) into soil evaporative (E) and plant transpiration (T) components remains challenging in flux modeling that has particular relevance to crop water use management. Here, we develop an approach to modify the Mapping EvapoTranspiration at high Resolution and with Internalized Calibration model (METRIC) that allows improved partitioning to landscape-scale flux components. Referred to herein as METRIC-2S, the approach introduces a two-source scheme into the original one source model, using soil and vegetation temperatures to drive the partitioning process. These temperatures are used by METRIC to calculate two ET components, one for the soil and another for the vegetation, which are subsequently weighted by the fractional vegetation cover (fc) to compute E and T. Soil and vegetation temperatures are estimated using the hourglass method, which is driven by the surface temperature and fc. ET estimates from the original METRIC and revised METRIC-2S models are intercompared and validated against eddy covariance measurements over three agricultural sites, including an olive orchard, wheat field and a mixed wheat/olive plantation. Overall, METRIC-2S provides considerable improvements in accuracy relative to the original METRIC model over the three sites, with observed decreases in RMSE from 141 to 63 W/m 2 at the olive site, 102 to 83 W/m 2 over the wheat field and from 180 to 78 W/m 2 at the mixed site. To evaluate the performance of the partitioning scheme, transpiration estimates are compared against available sap flow measurements over the olive orchard site for selected dates that coincide with a Landsat overpass, with an RMSE from this reduced sample of approximately 22.3 W/m 2 . While additional verification and assessment of component values are required, results suggest that the METRIC-2S approach represents a good trade-off between simplicity and improved accuracy. • METRIC-2S, is a two-source model derived from the METRIC approach. • METRIC-2S uses soil and vegetation temperatures to drive the ET components. • METRIC-2S model demonstrates significant ET improvements over the original METRIC. • Results of METRIC-2S transpiration compared to sap flow measurement is promising.