Identification of Trends in Precipitation Extremes and its Possible Impacts for the city of Tubarão, in Southern Brazil

Changes in patterns of extreme precipitation have been observed in different parts of the world, frequently being associated with climate change and global warming. Other factors, such as urbanization and land use change, also may contribute for alterations in regional climate. Understanding the behaviour and possible impacts of extreme precipitation changes is essential for urban planning and decision-making process. This study aims to identify potential signs of climate change with trends analysis in the urban area of the city of Tubarão, in Southern Brazil, using records of daily precipitation. We also discuss the possible impacts from the trends for public infrastructure and society. It is important to stress that this study does not aim to assess the causes of the increase.

The analysis was performed on basis of the precipitation indices of moderate extremes developed by ETTCDI and calculated by RClimDex software tools. These indices provide elements to identify trends in the characteristics of precipitation. We used the complete available data from Rio do Pouso station, whose record length is 69 years. Besides that, Rio do Pouso was the station used for generation of IDF curves for the design of hydraulic structures in the municipality.

The results produced show that almost all the indices have increased, with 95% confidence intervals, presenting positive trends for all the indices. The results induce a positive trend of extreme precipitation, either for total annual or daily maximum precipitation. Furthermore, using different base periods (1940-1969, 1961-1990 and 1988-2017), it is possible to predicate the increase of the frequency of very wet days (above 95^th percentile) and extremely wet days (above 99^th percentile). This increase also follows the increase of total annual precipitation suggesting that most of the precipitation occurs with high intensity. Seasonal analysis also presented an increase of the indices, mainly in summer and spring, inducing a possible relation with El Niño episodes.

Positive trends in precipitation extremes can cause several impacts for human life and urban infrastructure. With the increase of extreme precipitation values, hydraulic structures such as drainage network may become undersized, intensifying floods and increasing public health problems.

These results reinforce the importance of evaluation of the variability of precipitation data in the city of Tubarão to identify trends.