Evaporation Studies of Canopy-Covered On-Farm Reservoir

Abstract

The present study used fifteen existing evaporation models that use flux gradient, energy balance, and mass transfer approaches to estimate the rate of evaporation from a regular-sized open on-farm reservoir (OFR). Statistical analysis was performed to screen the models. The root mean square error (RMSE), percent deviation, coefficient of determination (R2), and scatter plot analysis reveal that three of fifteen models—namely, the Bowen ratio energy budget (BREB), Priestley-Taylor, and de Bruin–Keijman models—predict the evaporation rate from an open on-farm reservoir that is close to the actual evaporation recorded by a class A pan evaporimeter. These selected models were further used to predict the evaporation rate from a canopy-covered on-farm reservoir, taking into consideration the weather parameters in their microenvironment. The depletion of the water level in the OFR, which was recorded daily by a graduated staff gauge, and the change in the water spread area were measured together to compute the actual evaporation rate from the water bodies. The daily average evaporation rate from the canopy-covered OFR was approximately 1.18 mm less than the evaporation rate of a similar open OFR. During winter season (October to February), the 35% reduction in evaporation loss owing to the canopy cover over the OFR in comparison with the evaporation loss in an open OFR indicates the efficacy of the biological measure in mitigating the loss of scarce natural resources (e.g., rainwater) in rainfed areas.