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

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