This study assessed the impact of climate change on the hydrological regime of the Paraguaçu river basin, northeastern Brazil. Hydrological impact simulations were conducted using the Soil and Water Assessment Tool (SWAT) for 2020–2040. Precipitation and surface air temperature projections from two Regional Climate Models (Eta-HadGEM2-ES and Eta-MIROC5) based on IPCC5—RCP 4.5 and 8.5 scenarios were used as inputs after first applying two bias correction methods (linear scaling—LS and distribution mapping—DM). The analysis of the impact of climate change on streamflow was done by comparing the maximum, average and reference (Q90) flows of the simulated and observed streamflow records. This study found that both methods were able to correct the climate projection bias, but the DM method showed larger distortion when applied to future scenarios. Climate projections from the Eta-HadGEM2-ES (LS) model showed significant reductions of mean monthly streamflow for all time periods under both RCP 4.5 and 8.5. The Eta-MIROC5 (LS) model showed a lower reduction of the simulated mean monthly streamflow under RCP 4.5 and a decrease of streamflow under RCP 8.5, similar to the Eta-HadGEM2-ES model results. The results of this study provide information for guiding future water resource management in the Paraguaçu River Basin and show that the bias correction algorithm also plays a significant role when assessing climate model estimates and their applicability to hydrological modelling.
The Paraguaçu watershed in northeastern Brazil faces increasing water scarcity, with water resources unable to meet the increasing demand. Accurate assessment of water availability is thus essential for efficient planning and management of local resources. In this work, the potential of the SWAT model for predicting daily and monthly variability of the hydrologic regime of the Paraguaçu River was assessed. Model calibration/validation followed: (i) A hierarchical framework; (ii) the assessment of maximum, average and minimum streamflow based on paired t-test and linear regression analysis; and (iii) the definition of permanence curves for streamflow with a probability of occurrence of 90% (Q90) and 95% (Q95). The goodness-of-fit indicators revealed a “satisfactory” model performance (model efficiency ranged from 0.42 to 0.83) when predicting streamflow in monitored sub-basins using a unique set of parameters for wet and dry conditions. The flow duration curves also showed that the model underestimated higher flows resulting from extreme events but performed well for flows with exceedance probabilities of <90%. The regression analysis and paired t-test demonstrated that the SWAT model can be used for estimating maximum, average and minimum monthly streamflow in a region where information is insufficient to support water authorities in the decision-making process. The SWAT model can thus be considered adequate for simulating monthly streamflow in the Paraguaçu watershed.
Flow is one of the hydrological variables of greatest interest due to its connection with water availability and its multiple uses. However, in recent years this resource has been threatened by intense land use and climate change, affecting patterns previously considered to be stationary. The goal of this study was to evaluate trends in changes of patterns of flow, precipitation, and land use in a basin located in the Brazilian Cerrado. 33 years of rainfall, fluviometric, and land use data were used, covering the period of 1985 to 2018 on an annual scale. Mann-Kendall and Sen Slope’s nonparametric test was applied to evaluate the trends in temporal series, as well as the Spearman Rho and Pettit, which were used to analyze the correlations between variables and detect the point of change in the series, respectively. The results show statistically significant trends in flow reduction over time. At the same time, a considerable reduction in natural areas occurred, with an increase of +750% in agricultural areas. The results also show that although a tendency to reduce precipitation was detected, its magnitude was not significant, with land use changes being the main factor for the negative changes in the flow of the Rio Grande tributary.
A chuva é um fator ativo na erosão hídrica, sendo esta a mais danosa erosão para solos e água. Diversos métodos foram desenvolvidos para estimar o potencial da precipitação em desagregar partículas dos solos. Neste sentido, objetivo deste trabalho é estimar e mapear o potencial erosivo das chuvas, bem como o período de retorno e probabilidade de ocorrência na bacia hidrográfica dos Rios Galheirão e Roda Velha, situada no oeste da Bahia. Foram utilizados dados fornecidos de 14 estações convencionais da Agencia Nacional de águas e 20 pontos estimados por sensores orbitais (TRMM) disponibilizados pela Empresa Brasileira de Agropecuária. Os dados foram inseridos em fórmulas e posteriormente distribuídos espacialmente em ambiente SIG. Para análise comparativa dos resultados encontrados com o cenário de uso e ocupação do solo, foi utilizado o mapa disponibilizado pelo Mapbiomas. Os resultados indicam a estimativa de erosividade anual com valores de até 13,536.28 MJ.mm.ha-1.h-1 por ano. A região oeste da bacia possui os maiores índices erosivos nas áreas de intensa atividade agrícola, sendo mais intensa nos meses de maior lâmina precipitada. Os índices erosivos da bacia hidrográfica são considerados de baixa e média erosividade. Estimation of rain erosion (R) in a tropical basin in western Bahia Abstract: Rain is an active factor in water erosion, which is the most damaging erosion to soil and water. Several methods have been developed to estimate the potential of precipitation to break down soil particles. In this sense, the objective of this work is to estimate and map the erosive potential of the rains as well as the period of return and probability of occurrence in the hydrographic basin of the Rivers Galheirão and Roda Velha, located in the west of Bahia. Data provided from 14 conventional stations of the National Water Agency were used, 20 points estimated by orbital sensors (TRMM) made available by the Brazilian Agricultural Company, the data were inserted in formulas and later distributed spatially in a GIS environment. For comparative analysis of the results found the map provided by Mapbiomas was used with the land use and occupation scenario. The results indicate the annual erosivity estimate with values of up to 13,536.28 MJ.mm.ha-1.h-1 per year. Since the western region of the basin has the highest erosion rates that correspond to the areas of intense agricultural activity, being more intense in the months of greater precipitated depth. The erosive indices of the hydrographic basin are considered of low and medium erosivity.
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