Impacts of land cover changes on energy flow and the water cycle in the brazilian semiarid region

Abstract

The São Francisco River is the most important water resource in the Northeast of Brazil, as it corresponds to 70% of the region's water availability, crossing the most populous semi-arid area on the planet. Its waters have multiple uses, for purposes of domestic consumption, irrigation, hydroelectric power generation, navigation, leisure, tourism, among others. Due to its significant strategic importance in the regional context, this river has undergone strong water stress over the last decade and, probably, this situation will continue, or even worsen, in the coming years. The reason for this is the strong demand for the withdrawal and consumption of its water, especially for the irrigation of agricultural crops. Such demand has increased even more, given the execution of the São Francisco River Integration Project (PISF), which already transposes part of its waters to the hydrographic basins of the Northern Northeast, territories that suffer from severe water shortages and have a high demand for water, both for domestic consumption and for carrying out productive activities. In addition, climate projections for the coming decades predict significant drops in rainfall volumes in the São Francisco River Basin, a situation that has already occurred between 2012 and 2018, and which resulted in a high decrease in flows, impacting various sectors, such as generation electricity and agricultural activities. Given this context, this research sought to assess the impacts of changes in land cover on the energy flow and on the hydrological cycle, especially for the estimation of precipitation and its effects on water availability in the Brazilian Semiarid Region. It was found that the São Francisco River Basin has undergone relevant changes in its land cover over the last four decades, with the deforestation of native vegetation in substitution for pastures and agricultural crops, and that these changes have significant relationships with reduction of water infiltration into the soil and subsurface runoff, in addition to the increase in surface runoff and evapotranspiration. Altogether, rainfall volumes have been decreasing since the 1990s, accompanied by reductions in the flow of the São Francisco River. The fall has been occurring more intensely since the last decade, in a strong event of drought that hit the basin and the Brazilian Semiarid Region between 2012 and 2018. In this event, the long-term flows of the São Francisco were the lowest in the whole historical record, impacting the generation of hydroelectric energy in plants located in the Sub-Middle and Lower São Francisco hydrographic sub-regions, and enabling the intrusion of saline water from the Atlantic Ocean, reducing water quality kilometers inland from the continent in the São Francisco gutter. Keywords: Climate Alterations. Drought. Land Use. São Francisco River.