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• Evaporation trends of tropical reservoirs in Brazil were investigated. • Both positive and negative trends in evaporation were observed. • In the industrial region, the negative trend was potentially caused by the impact of pollutant released to the atmosphere. • In the coastal region, the positive trend was related to increasing air temperature. This paper aims to analyze the trends (Mann-Kendall test) of evaporation and climatological variables, including air temperature, relative humidity and wind speed in four reservoirs located in the Brazilian Northeast. The evaporation was estimated through remote sensing using the Surface Energy Balance System for Water (AquaSEBS) model from 1985 to 2018. In addition, it was verified which meteorological parameter has the highest correlation (R2) with the evaporation in order to assess why this process is changing throughout the years in each reservoir. The model performed well, with root mean square error (RMSE) ≤ 1.25 mm/day, percent bias (PBIAS) ≤ 13.70% and coefficient of determination (R2) ≥ 0.51. One reservoir located closer to a coastal zone presented a positive trend (+0.24 mm/34 years), corroborating the measurements of a reference class A pan, and Penman-Monteith equation, while the others, located closer to industrial areas, displayed negative trends (−0.26 to −0.080 mm/34 years). This reduced evaporation was attributed to the impact of industrial pollutant release to the atmosphere, while the increasing effect in the other reservoir was due to its proximity to the coast, which implies an air renewal as the sea breeze contributes for an improvement in the air quality. The meteorological data also presented positive and negative correlations: Temperature exhibited a positive trend (+0.57 °C/34 years), whereas humidity (−4.83%) and wind speed (−0.29 m/s), a negative trend. Evaporation displayed moderate coefficient of determination (R2 > 0.31) with wind speed and humidity. Yet, the reduction of evaporation may be associated with a possible counterbalancing effect of wind speed over humidity. Overall, the results contribute to a better understanding of evaporation trends in a water-scarce region and can be used in a water resources management context as the increasing/reduction of evaporation might significantly impact water availability in this area. [ABSTRACT FROM AUTHOR]

• Hydroclimatic conditions and water quality affect class A pan coefficients (K) • K-values were correlated with wind speed, air temperature and TP concentration. • Wind-induced phosphorus re-suspension potentially resulted in reduced evaporation. • The impact of K-values on evaporation was negatively related to water availability. 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. [ABSTRACT FROM AUTHOR]