FLOOD RISK ASSESSMENT IN PORTO ALEGRE-RS
Keywords:
floods, time of recurrence, non-stationarity, climate changeAbstract
In May 2024, Porto Alegre experienced the largest flood recorded in 126 years (1899-2024), surpassing the historic 1941 event that led to the implementation of a Flood Protection System (SPCC) in the 1970s. Water levels in Guaíba Lake are influenced by upstream river basins, downstream hydraulic interaction with Patos Lagoon, and wind forcing. This study estimates future flood risk based on the adjustment of a non-stationary statistical distribution for the historical water level series. Different parameterizations of the Gumbel distribution were evaluated, and the model with the best statistical performance was selected. The two largest events in the record proved to be "outliers" suggesting that their return periods may exceed those estimated by the fitted model. Risk projections up to 2100 indicate a progressive increase in flood magnitude, ranging from 4% in 2030 to 10% in 2100. For the 100-year return period event, flood levels are projected to increase by approximately 10% by 2100. The results assume that the trend observed over the past 126 years adequately represents future non-stationarity, without explicitly incorporating prospective climate change scenarios driven by global environmental and economic activities.
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