Changing Trends in Rainfall Extremes in the Metropolitan Area of São Paulo: Causes and Impacts

Abstract

This study analyses observed trends in extreme rainfall events in the Metropolitan Area of São Paulo (MASP). Rainfall data sets with more than 60 years of record in MASP are used. In MASP, extreme rainfall events represent hydro meteorological hazards that trigger flash floods and landslides. Changes in rainfall extremes can be partly due to natural climate variability. In addition, it can also be related to global warming and/or urbanization. Total annual precipitation and the number of days with precipitation of 20 mm exhibit the largest significant increase during 1930-2019. This is better noticed during summer. This tendency is also noticed in the number of days with precipitation of 100 mm or more. Therefore, the positive trend in annual precipitation is mainly due to an increase in the frequency of extreme precipitation events. On the other hand, our analysis shows that the number of consecutive dry days increased. Though these results appear to be contradictory, they indicate an important climate change in recent times. Intense precipitation is concentrated in few days, separated by longer dry spells. The focus is on how atmospheric circulation variations are contributing to these changes. During 1960-2019 the South Atlantic Subtropical Anticyclone has intensified and slightly moved southwestward of its normal position. This change influences the transport of humidity and therefore impact precipitation. This can explain the increase in the precipitation extremes in the MASP. However, other atmospheric systems may also be important.

Dry and Wet Climate Periods over Eastern South America: Identification and Characterization through the SPEI Index

“…They also analyzed the relationship between the phases of the Southern Annular Mode (SAM) and the position of the SASA. Although the focus of the Marengo et al 2020 [44] was the climate variability impact in a metropolitan city in the ESA, their large-scale analysis clearly shows the humidity flux variability coming from the South Atlantic Ocean toward the region. Changes in the circulation can be important for the increase in the extreme wet and dry events observed in the period.…”

“…Attribution studies to identify whether the increase in the frequency of the wet and dry events registered during the 1980-2018 period over the ESA are due to natural or anthropogenic causes are still being developed. However, some possible physical explanation was given by Marengo et al 2020 [44]. They found that changes in the position and intensity of the SASA are responsible for changes in the atmospheric circulation in the ESA.…”

Analysis of Dry and Wet Episodes in Eastern South America during 1980-2018 Using SPEI

“…The 3rd International Electronic Conference on Atmospheric Sciences (ECAS 2020), 16-30 November 2020; Sciforum Electronic Conference Series, Vol. 3, 2020 of consecutive dry days also observed in MASP [8] indicates that intense precipitation is concentrated in fewer days, separated by longer dry spells.…”

“…In the last decade, the 2014 drought over Southeastern Brazil affected the water supply in the Metropolitan Area of Sao Paulo (MASP), one of the most populous areas in South America [3]. On the other hand, the observed positive trend in the frequency and intensity of extreme rainfall events in MASP, particularly during the austral Summer, triggers flash floods and landslides over the area [7,8]. The increasing number…”

“…Focusing on how the atmospheric circulation may contribute to these climate changes in MASP, Marengo et al [8] verified that during the last six decades the South Atlantic Subtropical High (SASH) has intensified and slightly moved southwestward of its normal position, probably affecting the transport of humidity towards South America and the precipitation associated.…”