Extreme Rainfall Events in the Southwest of Rio Grande do Sul (Brazil) and Its Association with the Sandization Process

Abstract

Part of the sandization process in southwestern Rio Grande do Sul (Brazil) originates from daily torrential rains. However, it is believed that climate changes have been provoking more frequent and more intense rains in the region, a phenomenon which can change the dynamic of erosion/transport/sedimentation natural processes. The objective of this work is to identify the behavior of daily rainfall extreme events (in terms of their frequency, return time, tendency and genesis), relating them to both climatic change issue and enhancement of erosive processes. We have used daily rainfall data from meteorology stations of Brazilian National Water Agency (ANA) for the period between 1928 and 2017 and the percentile 99 was used to identify daily rainfall extreme value (71.5 mm). The upper values were categorized and their absolute and relative frequencies as well as their return time were identified. The temporal tendency of these events was evaluated by the Mann-Kendall test, considering the 90 years of the series. The results showed that there was a significant increase in heavy rainfall events in November and December in the last two decades and that the return time for these events decreased throughout the time. Synoptic analyses from GOES 13 satellite infrared imagery and from ECMWF/ERA/Interim reanalysis data allowed concluding that such intense rainfall events originated themselves from the transport of moisture from the Amazon by Low-Level Jets, which promoted the formation of Mesoscale Convective Complex, with large volumes of rain in the study region. Thus, the recurrence of these events in the southwest of Rio Grande do

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