Balanço hídrico de florestas e pastagens em diferentes solos na bacia hidrográfica do Bonfim – Região Serrana do Estado do Rio de Janeiro

Abstract

The water balance (WB) accounts for the volumes of water entering and leaving a specific area over a given time period, climate, and land use and cover systems. Estimating these volumes helps evaluate the need to implement appropriate surface and subsurface water resource management strategies, allows for strategic conclusions about the hydrological regime, and is one of the most important tools for land and water resource use planning in a watershed. Using the WB to assess ecosystem services related to water is crucial for supporting decisions related to land use changes. Estimating the water volumes of the water balance components helps understand how changes in land use and cover associated with a particular soil type can alter the hydrological cycle. The objective of this study was to estimate the water volumes of the main WB components considering different land uses and cover (Pastures and Forests) and soils (Cambissolo Háplico, Latossolo Vermelho, and Neossolo Litólico). The study period was from 01/01/2000 to 31/12/2019. The HYDRUS-1D model, using Richard's equation, was applied to estimate the water volumes in the WB. Pedotransfer functions were used to determine the soil hydraulic parameters for water retention and conduction. Upper boundary conditions included daily precipitation and evapotranspiration data, while lower boundary conditions included free drainage. Water uptake by roots was considered as an additional factor in Richard's equation (Sink factor). The results obtained were similar to those found by other authors; the average annual rainfall was 1462 mm, and the potential evapotranspiration was 1026 mm. In areas with Cambissolo Háplico under degraded pasture, 83%, 7%, and 9% of the total rainfall were percolated, transpired, and evaporated, respectively. In areas with Latossolo Vermelho under forest: these values were 35%, 58%, and 7%. During the dry season, evapotranspiration was 27% of the annual average precipitation in Latossolo Vermelho under forest and 11% in Cambissolo Háplico and Neossolo Litólico under pasture. Dry season percolation was 20% in Latossolo Vermelho under pasture and 9% in Latossolo Vermelho under forest. Surface runoff for a rain event with an intensity of 25 mm h-1 was 33% and 35% in pasture and 24% and 28% in forest. Soil characteristics play a fundamental role in WB calculations, affecting water percolation and evapotranspiration. This study highlights the importance of WB in water resource management, providing valuable insights for decision-making. Additionally, the data from this study can significantly contribute to future research and guide the development of policies and master plans, especially in the context of land use and cover.