Temporal Trend and Estimation of the Hydrological Risk of Maximum Rainfall and Flow Extremes in the City of Rio Branco, Acre, Brazil

Abstract Extreme hydrological events have gained notoriety in recent decades, thus recommended elements of decision-making assistance are important. In this context, this study focused on analyzing the temporal behavior of the maximum rainfall and waterflow recorded in the city of Rio Branco, Acre (Brazil), in addition to analyzing their frequencies, highlighting the reference quantiles and their reported probabilities of recurrence. The results pointed to a linearly upward trend, both for flow and rainfall, but these differences were not statistically significant according to the Mann-Kendall and Spearman Rho tests (α = 5%), leading to the conclusion for the occurrence of changes in hydrological patterns in Rio Branco, although statistically non-significant. However, it is warned to the precocity of attributing the main cause of such changes to either anthropic or natural actions. Regarding frequency analysis, it was found that Gumbel distribution is proper to the adjustment of the studied data, thus, it is possible to determine the lifetime associated with hydrological risk and the useful lifespan of a project aiming at planning actions in the face of the impacts of extreme events, especially in a scenario of severe floods.