Cloud effects on evaporation at a sub-tropical site

Abstract

Water usage impacts the management of our water resources. It is believed that accurate information on the hydrological cycle disseminated to the public, will considerably alter consumer usage behaviour. Evapotranspiration is one of the most variable and sensitive of the hydrological components and it is imperative that we fully understand what environmental factors directly or indirectly affect evapotranspiration. The objective of this study was to confirm the indirect affect of clouds on evaporation by examining how clouds affect variables used by the Penman-Monteith equation. As expected, during the day or night it was found that clouds had a negative correlation with solar radiation and temperature, and a positive correlation with humidity all at the earth's surface. There was no significant relationship between wind speed and clouds except during the night. Correlation coefficients, with respect to cloud, for temperature and humidity varied only slightly from day to night, but interestingly wind speed showed a significant change from 0.077 to 0.264. These findings may suggest that there are some occasions when 'water-wise' activities, for example watering the garden at night to decrease potential evaporation, may not be as beneficial as previously thought.