Variations of evaporation in time and space I. Study of diurnal changes using evaporimeters and grass lysimeters

Abstract

Daily variations in measured and calculated evaporation rates were accounted for by changes in various weather factors, using simple and multiple regression analyses. Partial correlations indicated that solar radiation accounted for about 70% of the variations in water losses from dish evaporimeters, whereas the corresponding influences of temperature, vapour pressure deficit and wind, as individual factors, were about 35%, nil and 60 %, respectively. However, radiation, temperature and wind, as component factors, each showed a lower correlation with evaporation, whereas vapour pressure deficit showed a higher and significant correlation. The degree of association between evaporation and weather factors was greater when the number of daily observations used in the analysis was doubled. Multiple regression analyses showed that the combined effects of the four weather parameters were responsible for about 90 and 50 % of the observed variations in evaporation and transpiration rates, respectively. The rates of evaporation, calculated by the multiple regression equations, agreed well with evaporation observed on days other than those used for making the regression. Significant correlations were also found between evaporation from small dishes and a US Class A pan, and between evaporation and transpiration from grass in lysimeters.