A combination of urban sprawl and land use change and hydrodynamic forecasting models resulted in a methodology capable of providing geographic information that identifies the locations with the highest risk of flooding in cities, including those caused by extreme rainfall. The study is pioneering and was carried out based on data from São Caetano do Sul, in the metropolitan region of São Paulo. The city was chosen because it has experienced extreme flood events. “Since this was something pioneering, it was essential that the city was not too extensive and with stable boundary conditions for the convergence of the model. In addition, the city had hydrometeorological data and documentation of the impacts of recent floods with public access”, explained researcher Cláudia Maria de Almeida, from the National Institute for Space Research (Inpe), where she coordinates the Cities Laboratory, focused on theoretical and research research. application in urban remote sensing. In partnership with the federal universities of Paraíba (UFPB) and Rio Grande do Sul (UFRGS) and local bodies, the researchers tested the model with data from the Civil Defense of the municipality, considering the flood of March 10, 2019, when three people drowned and several streets in São Caetano do Sul were left with almost two meters of water. The preliminary results of the study, which receives support from the State of São Paulo Research Foundation (Fapesp), were published in Water magazine. They are part of the work of doctoral student Elton Vicente Escobar Silva, also from INPE, the first author of the article, supervised by Claudia Maria. Modeling For hydrodynamic modeling, the group of researchers used the Hec-Ras software (Hydrologic Engineering Center’s River Analysis System). It is a computer program that can simulate the flow and elevation of the surface of the water, in addition to the transport of sediments. In the analysis of the extent of areas subject to flooding, two digital terrain models (DTM) were adopted with different spatial resolutions – 0.5m and 5m. The DTM is a mathematical representation of the ground surface, which can be manipulated by computer programs and usually represented in the form of a rectangular grid, in which an elevation value is assigned to each pixel. Vegetation, buildings and other features are digitally removed. Furthermore, four different computation intervals (1, 15, 30 and 60 seconds) were adopted to evaluate the performance of the simulation outputs. The best results were obtained with the 5m spatial resolution simulations, which showed the flood maps with the greatest coverage of the flooded points (278 out of a total of 286 points, that is, 97.2%) in the shortest calculation times. They even mapped flooding points that were not observed by the Civil Defense, nor by people from São Caetano do Sul during the flood that hit the city. “Our idea was to create a support methodology for decision makers. We simulate how soil change will be in the coming years and also what this impacts on the river runoff network. From there, it is possible to make simulations with scenarios. An example is to cross the millimeters of rain in a certain time interval to project what it can cause in an area of the municipality. With this, managers could make decisions to avoid both economic damage and loss of life”, said researcher Elton Vicente Escobar Silva. Connected with the capital and neighboring Santo André and São Bernardo do Campo, the municipality of São Caetano do Sul has a history of floods – there were 29 occurrences between 2000 and 2022, according to the researchers. On the other hand, it is the most sustainable city among the 5,570 in Brazil, according to the Sustainable Development of Cities Index (IDSC). And, with an estimated population of 162,000 residents, it has 100% of households with adequate sanitary sewage, 95.4% of urban households on public roads with trees and 37% on roads with adequate urbanization (presence of culvert, sidewalk, paving and curb), according to the Brazilian Institute of Geography and Statistics (IBGE). Example The experiment may be used by other municipalities in the construction of public policies and in decision-making to face the impacts of these phenomena, being able to avoid, in addition to the destruction of buildings and infrastructure, the death of residents, point out the researchers. In addition, it has low cost. “Once the research is completed, the transferability of the model will fundamentally depend on the availability of data to feed the model and on the training of personnel to parameterize and calibrate the model. The platform where the model runs is free for academic purposes and non-profit institutions only. For government institutions and companies, a modest annual license fee is charged, which is fully feasible for the vast majority of Brazilian cities,” said researcher Cláudia Maria de Almeida. The platform and the training of technical personnel are low-cost investments. “The data, if available, do not imply investment of public resources. However, obtaining data that is not available may entail costs, which, depending on the size of the city hall, will be easily covered”, explained researchers Cláudia Maria de Almeida and Elton Vicente Escobar Silva. Smart cities For researcher Claudia Almeida, a differential of the study is, in addition to combining hydrodynamic modeling for the urban area with the complexity of the underground rainwater drainage network, using real data to parameterize and validate the model. “We combine very high spatial resolution images and deep learning [aprendizado profundo]. All of this is linked to big data and smart cities”. The concept of smart cities began to be discussed in the 2010s, involving technological issues such as integrated traffic lights or bus stops with Wi-Fi. Recently, they began to include themes related to sustainability and quality of life for residents. According to the United Nations (UN), the world population reached eight billion people last year, with 56% living in urban areas. It is estimated that by 2050 the population will grow to 9.7 billion people, of which 6.6 billion will be in cities (about 68% of the total). City planning City planning, however, does not move at the same speed. With rampant urbanization there are, for example, changes in land use and land cover, an increase in the impermeable surface area and changes in hydrology. This scenario, combined with a higher frequency of extreme events caused by climate change, exposes municipalities to vulnerabilities such as floods, floods and landslides during the rainy season. Rains and floods harm the development of cities – Gabriel Correa/Agência Brasil “The disorderly growth of cities is contemplated in the research, since the hydrodynamic simulation model will be fed through a coupling, by the output of a spatial dynamic model of prediction of urban expansion and change in urban land use. Therefore, through the design of different scenarios of changes in land use, the hydrodynamic model will provide inputs for corrective actions, such as impeding urban occupation in floodplain areas of water bodies”, point out specialists from the National Institute for Space Research. The model is intended to simulate past events and predict future flood events, especially extreme ones, according to the conjecture of different scenarios. “At the same time, the model can and should be used as a decision support instrument with regard to planning and emergency actions by the Civil Defense and works to contain floods or floods”, said the technicians.
Agência Brasil
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