Estimativa, análise espacial e temporal da evapotranspiração de referência (eto) na bacia hidrográfica do Rio São Francisco, Brasil

Abstract

An important requirement for any water resources management program is knowledge of the natural processes that regulate the hydrological cycle, especially when it comes to spatial and temporal analyzes of these processes. The balance between precipitation and evaporation essentially defines water availability in a region. Irrigation planning and water resource management go hand in hand and when well executed, promote the maintenance and preservation of water resources without loss of productivity. In this context, the objective of this work was to perform a spatial and temporal analysis of reference evapotranspiration via Penman-Monteith FAO56 in relation to irrigated agriculture planning for annual crops and climatic trends of the meteorological variables in the São Francisco river basin. Meteorological data from the National Institute of Meteorology (INMET) were used and cover the period from 1961 to 2015. From this historical series, a spatial modeling of ETo and the zoning of annual crops in the São Francisco basin were performed in response to local water demand, relief and soil type. In the ETo determinations, the Penman-Monteith method - FAO 56 was used. Given the climatic trends determined by the Maan-Kendal test, the weight of each meteorological variable in the ETo calculation was determined. Spatial analysis in the São Francisco River basin showed that total annual ETo ranged from 1216.8 mm to 2114.2 mm. The sub-region São Francisco is the one that presented greater water demand, in the region of the Upper São Francisco, in turn, the zones with the milder regions were observed. A simulation of scenarios for the implantation of the corn crop showed that its viability under dry cultivation has a maximum arable area of 40% of the territory of the basin during the periods of planting beginning in January and / or February, November and / or December. Almost the entire territory of the basin is located in zones of water deficit, mainly in the periods of planting that go from the month of May until September. In the final compute of the ETo, there is a marked difference in influences of meteorological variables. On monthly scale, the relative humidity of the air, has greater contribution, followed by solar radiation. On a daily basis the roles are reversed, solar radiation has a greater impact on the calculation of ETo. The temporal analysis shows that the current scenario of the basin is that more than 80% of the territory of the basin presented an increase of the evapotranspiration rates in the order of 2.424 mm year-2.