EVAPORATION FROM BARE ARID SOILS: WEIGHING LYSIMETER MEASUREMENTS AND SIMULATIONS

Desert soils account for about a third of the Earth’s land surface. The mechanisms governing their water and energy fluxes remain poorly understood, which limits our understanding of the ecology and hydrology of desert environments. The goal of this study was to gain insight into evaporation from bare, arid soil using a process-based evaporation model in conjunction with evaporation data from a weighing lysimeter. Evaporation rates after three storms were simulated with the model and then compared to measured evaporation rates from the weighing lysimeter. The forward-simulations agreed well with measured evaporation rates for two out of the three selected storm events (evaporation rate RMSEs of 0.092 and 0.190 mm d^-1, respectively). For the third event, forward simulations systematically underestimated measured evaporation rates. The latter was likely due to differences between the soil moisture profiles found in the lysimeter compared to the one assumed by the model. Two sensitivity analyses were carried on. One was based on varying individual variables one by one and the other using multiple variables together using a Monte Carlo simulation. The sensitivity analysis showed that total porosity and difference in soil moisture content above and below the second drying front are the models most sensitive parameters. Since total porosity can be accurately measured, a better parametrization of the soil moisture profile would be required to further improve the model predictions for arid soils.