Performance of evaporation estimation methods compared with standard 20 m2 tank

Abstract

The low reliability of evaporation estimates in reservoirs challenges the management of water resources, especially when drought occurs. The evaporation rates measured in buried tanks (20 m2 evaporimeters) are close to that of lakes. However, there are few studies in Brazil using long data sets with this type of tank. In this context, this study aimed to evaluate evaporation estimates of free water surface using the method of Penman (1948) and other five empirical equations in comparison with data from a 20 m2 tank observed during 10 years. The annual relationship between rainfall and evaporation was 1.0, showing variations in dry years (0.7) and rainy years (1.3). Among all evaluated methods, Linacre (1993) shows the best performance. Camargo et al. (1999) has very good estimates using air temperature as input variable and is a simple and reliable alternative when data are missing.

Hydrological trade-offs due to different land covers and land uses in the Brazilian Cerrado

“…3a). It was approximately 100 mm yr −1 lower than the average observed during the last 37 years (Cabrera et al, 2016) due to a drought in 2014 (Getirana, 2015;Melo et al, 2016). Additionally, precipitation (P ) and the water balance residual (dS/dt) were the water balance components that had the largest variations throughout the monitoring period.…”

“…The soil root zone in the wooded Cerrado may reach up to 18 m (Rawitscher, 1948). However, most of the water used for plants' transpiration comes from the first layers (up to 7.5 m; Canadell et al, 1996;Oliveira et al, 2005;Garcia-Montiel et al, 2008).…”

“…This happens due to the lack of water readily available for the plants along the root zone. This condition does not repeat in the wooded Cerrado, as its root system is deeper (Canadell et al, 1996), and the plants may reach water in depths where sugarcane and pasture cannot do this. However, the root zone depth of undisturbed vegetation such as the wooded Cerrado is uncertain and may vary according to the soil characteristics (Canadell et al, 1996) and the groundwater table level (Leite et al, 2018).…”

“…The climate in the region is humid subtropical (Cwa, Köppen), with a hot and wet summer and a dry winter (Alvares et al, 2014). The average annual rainfall and temperature are 1486 mm yr −1 and 21.5 • C, respectively (Cabrera et al, 2016). Additionally, the soil is sandy, and it is classified as an entisol (Oliveira et al, 2016); its saturated hydraulic conductivity ranges from 11.30 to 147.31 mm h −1 along the superficial layer (first meter; Oliveira, 2014;Youlton et al, 2016b).…”

Alterações no ciclo hidrológico e na perda de solo devido aos diferentes usos do solo e variações climáticas em área de Cerrado

“…O método de Priestley e Taylor (1972) utilizado no cálculo da evapotranspiração do Cerrado sensu stricto pode resultar em estimativas com erros de aproximadamente 10% em relação aos dados observados (Vourlitis et al, 2002). A evaporação estimada para o solo exposto (superfície livre, sem vegetação) pode apresentar valores subestimados em até 11% (Cabrera et al, 2016), com os métodos utilizados (Priestley e Taylor, 1972;Ritchie, 1972 Fonte: Autor. Nas condições de solo exposto, as discordâncias entre dados observados e estimados podem ser explicadas pela dificuldade na manutenção do solo em preparo, sem a presença de plantas daninhas.…”