Estimativa espaço-temporal da recarga subterrânea em área de afloramento do sistema Aquífero Guarani, Brasil

Abstract

By virtue of the larger demands for fresh water and the costs of surface water treatment for many human activities (irrigation, tourism, domestic and industrial purposes), groundwater use was been gaining more attention. The Guarani Aquifer System (GAS) is one of the main sources of groundwater in the world, because of its water storage volume (~40.000 km3). After the last drought in Brazil Southeast (between the years 2013 and 2016), research about groundwater recharge of GAS intensified. However, the published studies just show mean estimates, at annual scale, from field measurements, inside small outcrop areas. The main objective of this study is estimate and spatialize the groundwater recharge of GAS at outcrop area inside the São Paulo state. Recharge was estimated and spatialized (1 km x 1 km) by the application of residual water budget method over month scale between October 2001 and September 2014. All other components of the water budget were obtained from remote sensing and land use/land cover maps. The surface runoff (hortonian overland flow) was considered in water balance. The novelty of this study is the spatialization of the multitemporal recharge estimates and the incorporation of the surface runoff component into the water balance, which has been neglected in the GAS recharge estimates. The results showed that the montly historical mean is 26 mm (±19 mm) and the annual historic mean is equal 307 mm (± 50 mm). January (67 mm) and December (57 mm) are the main months for recharge, with maximum estimates and more contribution of the area. On the other hand, the months with the lowest recharge estimates were August (7 mm) and April (8 mm). On average, recharge accounts for 16% of precipitation. The average monthly precipitation estimates only decreased as of October 2010. It was possible to observe the trend of evapotranspiration increase in 8.5 mm per year. This indicates the necessity to monitor land use in recharge areas. The variations in land use and occupation registered in the studied period (2001-2014) correspond mainly to variations in CNs of less than 5%. It was possible to identify the areas which that most allow rmore echarge, in average, center (62%), South (27%) and North (11%). In the dry periods the center (56%) and South (28%) stand out for the maintenance of the recharge. It is expected that the identification of these areas, as well as the spatialization of recharge estimates, may be useful for the management of water resources. The intensity and extent of areas subject to water insecurity will only increase if nothing are done in order to contain and / or eliminate the impacts of water use. Historical mean values can be used to limit water extraction values for the maintenance of these sources. In addition, the values may be useful for groundwater flow modeling studies.