Estimating dew formation in rice, using seasonally averaged diel patterns of weather variables

Abstract

If dew formation cannot be measured it has to be estimated. Available simulation models for estimating dew formation require hourly weather data as input. However, such data are not available for places without an automatic weather station. In such cases the diel pattern of weather variables might be used to run the simulation model. To investigate the possibility of using diel patterns of weather variables to estimate dew formation, a field experiment was carried out from February to April 1994 at the International Rice Research Institute (IRRI), Los Baños, Philippines. The seasonally averaged diel patterns of weather variables were derived from hourly records. Both the hourly recorded weather data and the seasonally averaged (‘mean’) diel patterns derived from these weather variables were used to run a simulation model based on an energy-balance approach. Hourly recorded weather data as input gave the best estimation of dew formation at crop height. Substituting the hourly records of wind speed and air temperature by their mean diel patterns gave slightly worse but still acceptable dew estimates, as confirmed by a Wilcoxon signed rank test. This test showed that for water vapour pressure and nocturnal net radiation, however, the substitution of actual values by mean diel patterns resulted in unacceptably large estimation errors.