Escassez hídrica e irrigação futura no Brasil: uma avaliação do impacto das mudanças climáticas nas principais culturas irrigadas do país

Abstract

Global warming will bring consequences to productive activities that depend directly on the climate, as is the case of irrigation. In Brazil, irrigation is an important and growing part of the country’s crop production, maintaining an annual growth rate of about four percent and with a significant potential for expansion. Therefore, this study analyzes the effects of global warming on total irrigation and its future impact on the country’s water scarcity for sugarcane, coffee, flooded rice and center pivot crops by considering the divergent RCP 4.5 and 8.5 scenarios. Reference evapotranspiration is calculated using the original Penman-Monteith method and a modification to consider the effect of carbon dioxide fertilization. Irrigation is calculated by the CROPWAT method with the soil water balance. The impact of total irrigation is done using regionalized AWARE characterization factors for Brazilian sub-basins. Future climate forecasts until 2100 came from the regional circulation model ETA – HadGEM-2-ES for South America and forecasts of irrigated areas in the country for 2019 and 2040 were considered. Irrigation results and impact for all crops were higher in the RCP 8.5 scenario, being more expressive for the central regions of the country due to the increase in temperature and absorbed radiation balance and decrease in relative humidity. The results of the carbon dioxide fertilization effect indicated a nationwide reduction in the trend of reference evapotranspiration, being more significant for regions with stronger winds. The sugarcane crop had the highest results for irrigation volume and future impact on water scarcity in both RCP scenarios because of its extensive irrigated area in the country. The impact was most significant for coastal northeastern planting regions, but central planting regions, which use mostly fertigation, had an expressive growth in irrigation and increase in future impact even with lower characterization factors. Rice had significant future impact values on water scarcity in its producing sub-basins due to significant values of characterization factors, while coffee had low irrigation and impact results if compared with rice and sugarcane, but its concentration in producing regions led to a high impact in the sub-basins of northwestern Minas Gerais and northern Espírito Santo. Although areas with single crops of sugarcane, rice and coffee presented the highest values of irrigation volume and impact for their sub-basins, the results showed considerable impacts in future periods for sub-basins with joint productions among the analyzed crops, including those of central pivot, in both RCP scenarios.