Diurnal Temperature Cycles in Shallow Water Pools

Larvas of malaria mosquito species live close to the water surface in shallow waters, and are exposed to water temperatures which differ considerably from the air or bulk water temperature. The present research aims to obtain a sound physical insight into processes which determine the water temperature profile. That is why, first, several outdoor experiments were made to collect physical evidence. Second, simple physical models are developed to simulate the temperature profile within small water bodies. The model simulations as well as the measurements show that during daytime strong temperature stratification occurs in relatively large water bodies (diameter > 1 m). This stratification is strongly dependent on wind speed and also on the vegetation of the surrounding environment of the water body. Throughout the night, however, a well-mixed layer develops growing from the water surface. Very small water bodies, however, mostly show a well mixed water layer during nighttime as well as during daytime. Model simulations agree well with the measurement results for relatively large water bodies (diameter > 1 m). Small water bodies (diameter <0.5 m), however, show a complex interaction between the atmosphere and the water-air interface and between the water body and the sediment below the water. It appears that the temperature behavior is very sensitive to the extinction coefficient for short wave radiation, which is closely related to the suspension of fine particles in the water. Subsequently, rain affects the water temperature dramatically during the rain event only. After such an event the normal course of the daily temperature cycle is more or less recovered.