Preliminary Analysis of the Evapotranspiration Coefficient for Different Land Uses in Lagoa da Conceição, Southern Brazil

Código

I-EBHE0176

Autores

José Henrique Hess, Patrícia Kazue Uda

Tema

WG 2.6: Water systems analysis for integrated planning & management

Resumo

The hydrological cycle includes evapotranspiration as one of its main components. The evapotranspiration coefficient is a multiplicative factor that ranges from 0 to 1, and it can be used to calculate the actual evapotranspiration of various surfaces by combining it with potential evapotranspiration. The Lagoa da Conceição watershed covers an area of 75.5 km², with approximately 30.7 km² of forest, 20.1 km² of water, 10.3 km² of dunes, 6.6 km² of grassland, and 6.5 km² of urbanized area. This basin is located in southern Brazil, on the island of Florianopolis, and has a subtropical climate with no defined dry season. There is a lack of research on evapotranspiration in the region. Remote sensing evapotranspiration products have been used worldwide to understand the spatial behavior of this term in the water balance. Therefore, the aim of this study was to carry out a preliminary analysis of the evapotranspiration coefficient of the Lagoa da Conceição basin, using 45 images from the Landsat 4-9 Collection 2 Level-3 Provisional Actual Evapotranspiration product, from 2017 to 2024, for different land uses in the Lagoa da Conceição basin. This analysis was carried out during the summer, rainy season (January to March) and the winter, less rainy season (July to September). The Wilcoxon-Mann-Whitney test, with a significance level of 0.05, revealed that areas of forest and grassland have a higher average evapotranspiration coefficient in the summer period compared to the winter period. The average coefficient of the forest was 12.67% higher during the summer period (cfor,sum = 0.931) than during the winter period (cfor,win = 0.827). For grassland, the average was 10.76% higher, with cgra,sum = 0.481 and cgra,win = 0.434. Dunes, urbanization, and water covers had lower coefficients in the summer period (cdun,sum = 0.341, curb,sum = 0.419, cwat,sum = 0.960) compared to the winter period (cdun,win = 0.485, curb,win = 0.499, cwat,win = 0.982), representing a decrease of 29.66%, 15.97%, and 2.32% respectively. It is understood that forests and water influence the behavior of evapotranspiration in the basin, as they cover most of it. Thus, these land uses control the evapotranspiration process in the basin, and since their respective evapotranspiration coefficients are higher, together with the potential evapotranspiration characteristic of these land covers, it is expected that the overall evapotranspiration of the basin will also be high. Further analysis will be carried out to elucidate the factors that influenced the results obtained.