Global climate predictions and possible environmental impacts have an increasing source of concern in recent years. Analyses of the impacts of climate change scenarios on regional hydrology are required to design effective adaptation strategies for specific river basins. This study focuses on assessment of future climate change impacts on water resources of the Mundaú River Basin (MRB), in Brazil, using the Soil Water Assessment Tool (SWAT) and Regional Climate Models (RCMs) Eta‐MIROC5 and Eta‐HadGEM2, for three time periods under two Representative Concentration Pathways (RCPs). In general, climate models predict that the MRB will experience significant annual precipitation decreases, between 0.4% (1,087.45 mm) and 25.3% (815.59 mm), in both scenarios (RCP 4.5 and RCP 8.5) respectively, when compared to the observed period (2003–2016). Maximum and minimum temperature increases up to 2.3°C and 0.65°C under the RCP 4.5 scenario, and up to 4.3°C and 2.2°C under the RCP 8.5 scenario. SWAT simulations predict substantial surface runoff decreases with a minimum average annual value of 21.3 mm for the RCP 8.5 in medium‐term. Additionally, actual evapotranspiration (ET) is predicted to decrease from 780.77 to a minimum of 648.1 mm, although increases in potential evapotranspiration (ET₀) are expected. In general, annual streamflow also is expected to decrease, more severely under RCP 8.5 conditions, reaching a drop of approximately 66.7% (15.2 m³·s⁻¹), compared to the observed period (45.5 m³·s⁻¹). Seasonal streamflow is predicted to decrease for both models, in both rainy and dry seasons, except for medium‐term of the Eta‐HadGEM2. Although there are still some uncertainties associated with climate models, the findings from this study can assist water resource managers in management decisions for appropriate water use, development of public policies that favour sustainability, and adoption of mitigation and prevention practices to ensure water security in the basin.

O Soil and Water Assessment Tool (SWAT) é um modelo hidrossedimentológico que tem como foco principal avaliar os impactos das modificações no uso do solo sobre a qualidade e quantidade de água em bacias hidrográficas. Para que essas avaliações sejam adequadas, considerando a representatividade dos processos simulados pelo modelo, faz-se necessário a realização do procedimento de calibração. Muitos modeladores encontram grande desafio nesta etapa imprescindível da modelagem. Há uma grande variedade de parâmetros a serem considerados, diferentes algoritmos, bem como diferentes funções objetivas. Outro aspecto a ser destacado é o fato de que o tempo de processamento pode ser alto, quando se considera bacias hidrográficas representativas, como é o caso da bacia hidrográfica do Rio São Francisco, Brasil (639.219km²). Para atender a demanda de criação de um modelo de gestão integrada de águas para países BIS (Brasil, Índia e África do Sul) sob cenários de mudanças climáticas, a bacia do São Francisco foi calibrada. Esta nota científica objetiva fornecer uma visão do procedimento de calibração e confiabilidade do modelo, utilizando dados de vazão em tempo mensal no período de 1961 a 2016 para a bacia do São Francisco. O modelo SWAT calibrado para a bacia do Rio São Francisco pode ser utilizado para análises de cenários de mudanças climáticas e seus impactos sobre a disponibilidade hídrica da bacia, subsidiando assim, a tomada de decisão sobre os recursos hídricos, e a criação do modelo de gestão integrada com os demais países do BIS.Palavras-chave: modelagem hidrológica, SWAT-CUP, BIS Calibration technique for modeling the São Francisco watershed, Brazil, using SWAT A B S T R A C TThe Soil and Water Assessment Tool (SWAT) is a hydrosedimentological model whose main focus is to evaluate the impacts of changes in land use on the quality and quantity of water in watersheds. For these evaluations to be adequate, considering the representativeness of the processes simulated by the model, it is necessary to carry out the calibration procedure. Many modelers find a great challenge in this essential stage of modelling. There are a wide variety of parameters to consider, different algorithms, as well as different objective functions. Another aspect to be highlighted is the fact that the processing time can be high, when considering representative watersheds, as is the case of the São Francisco River basin, Brazil (639,219 km²). To meet the demand for the creation of an integrated water management model for BIS countries (Brazil, India and South Africa) under climate change scenarios, the São Francisco basin was calibrated. This scientific note aims to provide an overview of the calibration procedure using flow data in a monthly time step from 1961 to 2016 in the studied basin. The SWAT model calibrated for the São Francisco River basin can be used to analyze climate change scenarios and their impacts on the water availability of the basin, thus supporting decision-making on water resources and the creation of a management model. integrated with the other BIS countries.Keywords: hydrological modeling, SWAT-CUP, BIS.

Modificações na cobertura vegetal do solo em bacias hidrográficas podem ocasionar alterações nas componentes hidrológicas. O objetivo do trabalho foi avaliar os processos hidrológicos sob diferentes condições de cobertura vegetal na Bacia Hidrográfica do Rio Mundaú (BHRM), Nordeste do Brasil, utilizando o modelo SWAT. Para a simulação hidrológica, foram considerados dois cenários (C1 – uso atual) e C2 (substituição de áreas agrícolas por Caatinga). Foram utilizados dados de entrada como mapa de uso e ocupação do solo, mapa digital de elevação e mapa dos tipos de solo, além de uma série de 17 anos de dados, em passo de tempo diário. A precipitação anual média da BHRM foi 1.109,7 mm, a evapotranspiração potencial anual foi 1.247,7 mm e a ascensão do aquífero raso foi de 24,94 mm por ano, em parte da bacia. O escoamento superficial anual para o cenário C1 foi igual 262,62 mm e para o cenário C2 igual a 257,49 mm. Os valores de percolação e recarga anuais foram de 302,78 e 15,14 mm para o cenário C1 e de 306,73 e 15,34 mm para o cenário C2. A evapotranspiração real anual para o cenário C1 resultou em 548,2 mm e para o cenário C2 em 549,3 mm. A mudança de uso do solo exerceu influência no regime hidrológico da Bacia do Rio Mundaú. A implantação de vegetação Caatinga em áreas agrícolas proporcionou redução no escoamento superficial. Por outro lado, processos como evapotranspiração, percolação para o aquífero raso e recarga para o aquífero profundo aumentaram.

ANÁLISE DA DINÂMICA TEMPORAL DA EVAPOTRANSPIRAÇÃO REAL EM UMA BACIA HIDROGRÁFICA DO SEMIÁRIDO ATRAVÉS DE MODELAGEM HIDROLÓGICA E SENSORIAMENTO REMOTO FREDERICO ABRAÃO COSTA LINS1; ABELARDO ANTÔNIO DE ASSUNÇÃO MONTENEGRO1; CAROLYNE WANESSA LINS DE ANDRADE FARIAS2; ALINE MARIA SOARES DAS CHAGAS1; RODRIGO DE QUEIROGA MIRANDA3 E JOSICLÊDA DOMINICANO GALVÍNCIO3 1Departamanto de Engenharia Agrícola, Universidade Federal Rural de Pernambuco, Rua Dom Manuel de Medeiros, s/n, Dois Irmãos, 52171-900, Recife, Pernambuco, Brasil. E-mail: frederico_acl@hotmail.com; montenegro.ufrpe@gmail.com; alinemschagas@gmail.com 2Departamento de Geociências, Universidade Federal da Paraíba, Campus I - Lot. Cidade Universitária, 58051-900, João Pessoa, Paraíba, Brasil. E-mail: carolynelins.ufpb@gmail.com 3Departamento de Geografia, Universidade Federal de Pernambuco, Av. Prof. Moraes Rego, 1235 - Cidade Universitária, Recife - PE, 50670-901, Recife, Pernambuco, Brasil. E-mail: rodrigo.qmiranda@gmail.com; josicleda@gmail.com 1 RESUMO A evapotranspiração é uma das componentes mais relevantes do ciclo hidrológico, especialmente, em regiões semiáridas, onde há elevadas temperaturas e alta demanda hídrica pelas culturas, sendo sua análise essencial para o planejamento e gestão dos recursos hídricos. Objetivou-se calibrar e validar o modelo Soil and Water Assessment Tool (SWAT) com informações de evapotranspiração real advindas de sensoriamento remoto, e investigar a sua dinâmica temporal em uma bacia hidrográfica experimental do Semiárido. O estudo foi desenvolvido na Bacia Experimental do Riacho Jatobá (13,5 km²). Dados de evapotranspiração (ET) foram obtidos do produto MOD16A2, do sensor MODIS. A simulação hidrológica foi realizada com o modelo hidrológico SWAT. Foram realizadas análises estatísticas descritivas e análise de tendência pelo teste de Mann-Kendall. Os valores de R² encontrados para a evapotranspiração, foram de 0,61 e 0,81 para a calibração e validação, respectivamente. As análises de tendência apontaram que há tendência de decréscimo da evapotranspiração real no período de 2006 a 2018. Da precipitação média anual na bacia (722,9 mm), 26% corresponde à precipitação efetiva e 74% retorna à atmosfera como evapotranspiração (534,7 mm). A utilização de dados alternativos para a calibração do modelo SWAT é de grande relevância, especialmente em bacias semiáridas. Palavras-chave: MODIS, SWAT, balanço hídrico. LINS, F. A. C.; MONTENEGRO, A. A. de A.; FARIAS, C. W. L. de A.; CHAGAS, A. M. S. das; MIRANDA, R. de Q.; GALVÍNCIO, J. D. ANALYSIS OF THE TEMPORAL DYNAMICS OF ACTUAL EVAPOTRANSPIRATION IN A SEMIARID RIVER BASIN USING HYDROLOGICAL MODELING AND REMOTE SENSING 2 ABSTRACT Evapotranspiration is one of the most relevant components of the hydrological cycle, especially, in semiarid regions, where there are high temperatures and great water demand for crops, and its analysis is essential for the planning and management of water resources. The objective was to calibrate and validate the Soil and Water Assessment Tool (SWAT) model with real evapotranspiration information from remote sensing, and to investigate its temporal dynamics in an experimental river basin of the Semiarid. The study was conducted in the Riacho Jatobá Experimental River Basin (13.5 km²). Evapotranspiration (ET) data were obtained from the product MOD16A2, from the MODIS sensor. The hydrological simulation was carried out with the SWAT hydrological model. Descriptive statistical analysis and trend analysis were performed using the Mann-Kendall test. The R² values ​​found for evapotranspiration were 0.61 and 0.81 for calibration and validation, respectively. The trend analysis test showed that there is a trend of decrease for actual evapotranspiration for the 2006–2018 period. Of the average annual precipitation in the river basin (722.9 mm), 26% corresponds to the effective precipitation and 74% returns to the atmosphere as evapotranspiration (534.7 mm). The use of alternative data for calibrating the SWAT model is highly relevant, especially for semiarid watersheds. Keywords: MODIS, SWAT, water balance.

Alluvial aquifers are vital for agricultural communities in semiarid regions, where groundwater quality is often constrained by seasonal and spatial salinity variations. This study employed geostatistical methods to analyze the spatial and temporal variability of electrical conductivity (EC) and the sodium adsorption ratio (SAR) and elaborate an indicative quality map in the Mimoso Alluvial Aquifer, Pernambuco, Brazil. Groundwater samples were collected and analyzed for cations, total hardness (TH), and the percentage of sodium (PS). Moreover, the relation between EC and the SAR was used to determine the groundwater quality for irrigation. Cation concentrations followed the order Ca²⁺ > Mg²⁺ > Na⁺ > K⁺. EC and the SAR exhibited medium to high variability, with spatial dependence ranging from moderate to strong, and presented a strong cross-spatial dependence. Results showed that sequential Gaussian simulation (SGS) provided a more reliable groundwater classification for agricultural purposes compared to kriging methods, enabling a more rigorous evaluation. Based on the strong geostatistical cross correlation between EC and RAS, a novel water quality index was proposed, properly identifying regions with lower groundwater quality. The resulting spatial indicator maps classified groundwater as suitable (64.7%), restricted use (2.08%) and unsuitable (2.38%) for irrigation. The groundwater quality maps indicated that groundwater was mostly suitable for agriculture, except in silty areas, also corresponding to regions with low hydraulic conductivity at the saturated zone. Soil texture, rainfall, and water extraction significantly influenced spatial and temporal patterns of groundwater quality. Such correlations allow a better understanding of the groundwater quality in alluvial valleys, being highly relevant for water resources management in semiarid areas.

Land-use change has a significant influence on runoff process of any watershed, and the deepening of this theme is essential to assist decision making, within the scope of water resources management. The study was conducted for Mundaú River Basin (MRB) using the Soil and Water Assessment Tool (SWAT) model. The study aims to assess the issue of land-use change and its effect on evapotranspiration, surface runoff, and sediment yield. Input data like land use, topography, weather, and soil data features are required to undertake watershed simulation. Two scenarios of land use were analyzed over 30 years, which were: a regeneration scenario (referring to use in the year 1987) and another scene of degradation (relating to use in the year 2017). Land use maps for 1987 and 2017 were acquired from satellite images. Overall, during the last three decades, 76.4% of forest was lost in the MRB. The grazing land increased in 2017 at a few more than double the area that existed in 1987. Changes in land use, over the years, resulted in an increase of about 37% in the water yield of MRB. Changes have led to increased processes such as surface runoff and sediment yield and in the decrease of evapotranspiration. The spatial and temporal distribution of land use controls the water balance and sediment production in the MRB.