Metodologia de balanço hídrico e critérios de outorga em bacias hidrográficas com uso intenso de reservatórios de pequeno porte estudo de caso na bacia do Rio Quaraí

Os reservatórios se constituem numa das principais formas estabelecidas pelo homem de modificar o ciclo hidrológico ao armazenar água para sua utilização no futuro. Em algumas regiões do país este mecanismo é de fundamental importância para o atendimento das demandas consultivas, seja pelas condições adversas do clima, como é o caso do semiárido nordestino, como também em função da alta demanda de água requerida para o atendimento da irrigação, como ocorre em algumas áreas do Rio Grande do Sul. Este trabalho apresenta uma metodologia de balanço hídrico em rios e reservatórios de pequeno porte, cujo foco é o atendimento aos instrumentos da Política Nacional de Recursos Hídricos, como a outorga de direito de recursos hídricos e as políticas de planejamento. A metodologia está baseada na integração entre o modelo hidrológico chuva-vazão MGB-IPH como recurso para obtenção das séries afluentes de cada reservatório e trecho de rio do sistema hídrico. Associado ao modelo hidrológico, está a integração com os Sistemas de Informações Geográficas, que possuem a vantagem de obtenção das características físicas da bacia de forma automática, facilitando também a associação com os objetos que representam o sistema hídrico (i.e. demandas e reservatórios). O modelo de simulação realiza a contabilização do movimento de água através de um sistema de reservatórios e trechos de rio, cuja progressão de cálculo é realizada de montante para jusante. Como técnica de otimização, foi utilizado o algoritmo SCE-UA, baseado na teoria dos algoritmos evolucionários. A metodologia desenvolvida foi aplicada na Bacia do Rio Quaraí, caracterizada pelo intenso uso da água para o atendimento das demandas da irrigação, e também pelo estabelecimento de centenas de pequenas estruturas de reservação de água, destinadas ao abastecimento destas demandas. Os resultados indicaram que não há água suficiente para o atendimento das demandas da irrigação em 100% do tempo. Em média, apenas 75% do volume total de água requerido para o atendimento das demandas atuais poderia ser atendido, considerando o período simulado de 20 anos. Nos anos mais críticos pode ocorrer o esgotamento do curso principal do Quaraí e outros locais, decorrência das retiradas de água, além do efeito da reservação de água pelos açudes, pois admitiu-se a hipótese de não existirem descarregadores de fundo nessas estruturas. Como alternativas para a gestão da água na bacia, apontam-se a definição de critérios de outorga para retiradas e liberação de água em reservatórios, além de implementação de novas estruturas de reservação e regularização.Reservoirs are the most important form established by the man to modify the hydrological cycle to store water for use in the future. In some regions of Brazil this mechanism is crucial to meet the advisory needs, either by adverse weather conditions, such as the semi-arid northeast, but also due to the high demand of water required to meet the irrigation, as occurs in some areas of Rio Grande do Sul. This work presents a methodology of water balance in rivers and small reservoirs, whose focus is to achieve the goals of the instruments of the National Water Resources Policy, as the water rights and the planning policies. The methodology is based on the integration between the hydrological rainfall-runoff model MGB-IPH as a resource for obtaining streamflow series from upstreams of each reservoir and for all sub-watershed defined on the water system. Associated with the hydrological model is the integration with Geographic Information Systems, which have the advantage of obtaining the physical characteristics of the basin automatically, it also facilitates association with objects that represent the water system (i.e. demands and reservoirs). The simulation model performs accounting for the movement of water through a system of reservoirs and river stretches whose progression calculation is performed from upstream to downstream. As optimization technique, the SCE-UA algorithm, based on the theory of evolutionary algorithms was used. The procedure was applied in the Quaraí River Basin, characterized by intense use of water to meet the irrigation demands, and also by the establishment of hundreds of small structures reservation of water, destined to supply these demands. The results indicated that there is not water enough to meet the demands of irrigation at 100% of the time. On average, only 75% of the total volume of water required to meet the current demands could be met, considering the simulated period of 20 years. In the most critical years can occur exhaustion of the main course of the Quaraí and other sites, due to withdrawals plus the effect of the reservation by dams, it admitted the hypothesis that there are no releases in this structures. As alternatives to water management in the basin, point the definition of licensing criteria for withdrawals and releases in dams, as well as implementing new reservoir with regularization structures

Integração do modelo hidrológico para grandes bacias MGB-IPH e sistemas de informação geográfica para suporte à decisão de outorga de direito de uso da água

Os procedimentos para decidir tecnicamente sobre pedidos de outorga de direito de uso da água envolvem etapas de comparação entre a demanda e a disponibilidade de água, as quais têm forte relação com os atributos espaciais da rede de drenagem e da localização dos diferentes e água em uma bacia hidrográfica. Idealmente, portanto, modelos hidrológicos utilizados para analisar a disponibilidade de água nos locais onde a outorga é solicitada deveriam ser integrados a um Sistema de Informação Geográfica (SIG). Neste trabalho apresentamos uma metodologia integração de modelos hidrológicos e SIG para auxílio à tomada de decisão em pedidos de outorga de direito de uso da água. A metodologia envolve: 1) a utilização de SIG para pré-processamento de dados visando a aplicação de um modelo hidrológico chuva-vazão; 2) a aplicação do chuva-vazão para gerar estimativas da vazão de referência adotada como disponibilidade hídrica em cada trecho de em que é dividida a bacia; 3) a transferência dos resultados do modelo hidrológico de volta ao SIG; e 4) a aplicação de um Sistema de Suporte à Decisão no qual cálculos simples Grande do Sul, de balanço hídrico são realizados internamente em um SIG. É apresentado um teste da metodologia na bacia do rio dos Sinos, no Rio Grande do Sul-Brasil, região em as demandas ultrapassam a disponibilidade de água. Os resultados no estudo de caso demonstraram que é possível aprimorar a metodologia de análise de outorga ao SIG e modelagem hidrológica para auxílio à tomada de decisão, facilitando assim o aproveitamento sustentável dos recursos hídricos numa bacia baseados no conhecimento da variabilidade sazonal e espacial da sua disponibilidade.The procedures for technical deciding about water use permits, involve steps of comparison between de‑ mand and availability of water which has a strong relation‑ ship between the spatial attributes of the drainage network and the location of different water users in a watershed. Therefore, ideally, the models used to make these analyses should be integrated into a Geographic Information System ‑ GIS. We propose a methodology for integrating GIS and hydrological models to support decision making in analysis of water use permits requests. The methodology involves 1) the use of GIS for pre‑processing of data for the application of a rainfall runoff hydrologic model; 2) the application of rainfall‑runoff model to generate estimates of the flow of reference adopted as water availability in every stretch of river; 3) transfer the results of the hydrological model back to the GIS; and 4) the application of a Decision Support System in which simple calculations of water balance are done entirely in GIS environment. The presented meth‑ odology was tested at the Dos Sinos River basin, at Rio Grande do Sul, Brazil, region where the demands exceed the water availability. The results of this case study showed that it is possible to improve the methodology used to analyze the granting of water rights for use permits when GIS and hydrological models are integrated

A new scenario-based framework for conflict resolution in water allocation in transboundary watersheds

One of the main causes of water conflicts in transboundary watersheds all over the world is represented by the increasing water demand due to urban, industrial, and agricultural development. In this context, water scarcity plays a critical role since, during a drought period, water supply is not su cient to cover the demand of all water uses. In this work, we have conceptualized and developed a new scenario-based framework able to improve the sustainability and equity of water allocation among two or more riparian countries. The proposed approach is in accordance with the United Nations Watercourses Convention. It considers a hydraulic/hydrologic model, a water-management model, and combines them with multi-criteria decision analysis (MCDA) and what if scenario analysis (WISA). The suggested framework was applied to the transboundary watershed of Cuareim/Quaraí river (Uruguay/Brazil) to tackle a real water-sharing conflict. It resulted in being very flexible in exploring various policy options and test and quantifying them with di erent scenarios to reach an objective and impartial decision in a water-sharing issue. This framework can e ectively be applied to any other transboundary watershed to resolve any possible conflict related to water-allocation/water-management matter

Patterns and drivers of evapotranspiration in South American wetlands

Evapotranspiration (ET) is a key process linking surface and atmospheric energy budgets, yet its drivers and patterns across wetlandscapes are poorly understood worldwide. Here we assess the ET dynamics in 12 wetland complexes across South America, revealing major differences under temperate, tropical, and equatorial climates. While net radiation is a dominant driver of ET seasonality in most environments, flooding also contributes strongly to ET in tropical and equatorial wetlands, especially in meeting the evaporative demand. Moreover, significant water losses through wetlands and ET differences between wetlands and uplands occur in temperate, more water-limited environments and in highly flooded areas such as the Pantanal, where slow river flood propagation drives the ET dynamics. Finally, floodplain forests produce the greatest ET in all environments except the Amazon River floodplains, where upland forests sustain high rates year round. Our findings highlight the unique hydrological functioning and ecosystem services provided by wetlands on a continental scale

Artificial neural network model of soil heat flux over multiple land covers in South America

Soil heat flux (G) is an important component for the closure of the surface energy balance (SEB) and the estimation of evapotranspiration (ET) by remote sensing algorithms. Over the last decades, efforts have been focused on parameterizing empirical models for G prediction, based on biophysical parameters estimated by remote sensing. However, due to the existing models’ empirical nature and the restricted conditions in which they were developed, using these models in large-scale applications may lead to significant errors. Thus, the objective of this study was to assess the ability of the artificial neural network (ANN) to predict mid-morning G using extensive remote sensing and meteorological reanalysis data over a broad range of climates and land covers in South America. Surface temperature (Ts), albedo (α), and enhanced vegetation index (EVI), obtained from a moderate resolution imaging spectroradiometer (MODIS), and net radiation (Rn) from the global land data assimilation system 2.1 (GLDAS 2.1) product, were used as inputs. The ANN’s predictions were validated against measurements obtained by 23 flux towers over multiple land cover types in South America, and their performance was compared to that of existing and commonly used models. The Jackson et al. (1987) and Bastiaanssen (1995) G prediction models were calibrated using the flux tower data for quadratic errors minimization. The ANN outperformed existing models, with mean absolute error (MAE) reductions of 43% and 36%, respectively. Additionally, the inclusion of land cover information as an input in the ANN reduced MAE by 22%. This study indicates that the ANN’s structure is more suited for large-scale G prediction than existing models, which can potentially refine SEB fluxes and ET estimates in South America