The influence of hydroclimatic conditions and water quality on evaporation rates of a tropical lake

Abstract

The present paper analyses the influence of hydroclimatic forcing and water quality on the evaporation process of Lake Santo Anastácio, a tropical lake with capacity of about 0.4 hm3 and maximum depth of 5 m, located in the city of Fortaleza, Ceará, Brazil. The two-dimensional model CE-QUAL-W2 was used for modelling hydrodynamics and direct evaporation from the lake, and an evaporation estimation equation based on the mass transfer method was calibrated. Subsequently, direct evaporation was modelled while, at the same time, thermal characteristics of the water column were examined. Then, modelled evaporation was compared to measurements obtained over a period of 11 years (2009–2019) with a Class A pan. The results indicated a daily thermal stratification of up to 2 °C. When modelled evaporation was compared with the measurements obtained with the Class A pan, the mean Class A pan coefficients (K) were between 0.66 and 0.69, lower than the values reported in literature, possibly due to the high concentration of pollutants in the lake. Finally, the K coefficients were negatively correlated with wind speed (R2 of 0.51; p-value < 0.05), air temperature (R2 of 0.67; p-value < 0.05) and total phosphorus concentration in the dry period (R2 of 0.41; p-value < 0.05); suggesting that wind-induced phosphorus resuspension attenuated evaporation rates in the lake. These results confirm the direct influence of hydroclimatic conditions and water quality on the evaporation rates of a tropical lake. The impact of different K-values on water availability was also investigated. The results of this study are important to assist in management operations of lakes and reservoirs, mainly in regions which are substantially impacted by evaporation, as is the case of the Brazilian semiarid.