Effects of diurnal, intra-seasonal and seasonal climate variability on the energy balance of a small subtropical reservoir

Abstract

In order to gain a full understanding of the importance of interactions between the atmosphere and inland water bodies, there is a need to analyse these exchanges in different regions throughout the world and under a wide range of weather and climate conditions. A 2-year time series of energy balance measurements was made at a small reservoir situated in southeast Queensland, Australia. Measurements were used to establish diurnal, intra-seasonal and seasonal cycles of evaporation, while synoptic weather maps and local weather station data were used to relate variations in water surface-atmosphere energy exchanges to synoptic and mesoscale weather phenomena. Consistent diurnal peaks in latent heat flux during the afternoon were observed throughout this study as a result of strong dry winds coinciding with peak water surface temperatures. Occasional intra-seasonal pulses in latent heat flux (i.e. evaporation) in winter and spring were associated with the passage of cold fronts over southern Queensland, which brought strong dry westerly winds. The average annual evaporative water loss from the reservoir during the 2-year measurement campaign was 991mm year-1. It is thought that differences between the annual evaporation totals for the 2 years of this study may have been related to differences in the frequency of overcast conditions as a result of a change in the phase of the El Nino-Southern Oscillation.