Impactos das mudanças climáticas sobre as demandas de água para irrigação de culturas de sequeiro na região Sul e Campanha do Rio Grande do Sul

Abstract

Changes in climatic variables directly interfere with agricultural production in a given region, and can cause major impacts. The southern half of Rio Grande do Sul, which comprises the South and Campaign regions, is a major producer of various crops. The southern half is considered to be at its maximum limit of cultivable areas, in addition to presenting lower rainfall regimes than the northern half. Thus, it is essential to properly manage the natural resources available in order to obtain greater agricultural productivity, avoiding losses. CPTEC/INPE makes available on the PROJETA platform, global climate models regionalized by the ETA model, which enable better results for modeling in specific areas. The SWAP (Soil Water Plant Atmosphere) model makes it possible to simulate interactions between water flow, plant growth, heat flow and solute transport. Thus, this work aimed to evaluate the influence of climate change on the demand for water for irrigation using three global climate models regionalized by the ETA model (CANESM2, HADGEM2-ES and MIROC5) for the historical period and two future scenarios RCP 4.5 and RCP 8.5, which were subdivided into three periods: F1 (2006-2040), F2 (2041-2070) and F3 (2071-2099), for 27 municipalities that are located in the South and Campaign in Rio Grande do Sul. an analysis of the trend of precipitation data and average temperature for the time periods and verified the existence of positive anomalies. It was possible to observe the trend of increasing average temperature throughout this century, where the highest temperatures will occur at the end of the century. For the three climatic models, temperatures in general will be milder in the RCP 4.5 scenario when compared to the RCP 8.5 scenario. There is a tendency to increase the average accumulated precipitation in the future periods analyzed. As a result, although most municipalities and models indicate an increase in rainfall patterns, there are variations between municipalities, models and scenarios. The water demands of the southern region and Campaign showed variations between scenarios and models, however it is possible to conclude that some scenarios and models project the increase of water for irrigation for some municipalities, and others indicate a decrease in the demand for water for irrigation, when compared with the base period. Such increase in water demand observed may be related to the increase in average temperature that occurs until the end of the century, causing the transpiration of crops to increase and also the evaporation of water available in the soil, which consequently increases the demand for water for irrigation. It should be noted that due to the fact that crops vary significantly in the planted area each year, since crop rotation is a widely used technique, the results are only projections since they use the areas and crops for the year 2017 made available by the Foundation Economics and Statistics (FEE), for rainfed crops.