Estimating the Effect of Heat Storage on Evaporation Rates

In the development of the Penman model, the effect of heat storage on evaporation rates was considered to be negligible in comparison with the net radiant heat. Comparison of mean daily evaporation rates observed using a floating pan and evaporation rates computed using the Penman model indicated that heat storage may be an important factor controlling evaporation rates from a pond during the period from April to August. A linear regression equation relating the residuals of the observed and computed evaporation rates to the radiation of the previous day can be used to adjust the Penman estimates for the effect of heat storage. The equation reduced the heat storage hysteresis without requiring additional meteorological data.