Extreme rainfall days in metropolitan Sao Paulo have risen four-fold in seven decades

Cemaden operators in the scenario space. Credit score: Cemaden

Intense rainfall has become increasingly widespread in metropolitan São Paulo, Brazil. The capital of the condition of São Paulo is the major city in the southern hemisphere. The metropolitan area endured from flooding owing to large rain in February. Early in the month, no much less than 114 millimeters (mm) fell in a single 24-hour time period. This was the next highest 24-hour amount of money for the thirty day period due to the fact 1943, according to Brazil’s Countrywide Meteorological Institute (INMET).

According to a study by researchers at the Purely natural Catastrophe Surveillance and Early Warning Middle (CEMADEN), an company of the Brazilian Ministry of Science, Engineering, Innovation and Communications (MCTIC), the two the complete rainfall and the frequency of extraordinary rainfall activities in metropolitan São Paulo have greater drastically in the last seven many years.

Whilst there had been almost no days with heavy rain (extra than 50 mm) in the 1950s, these days have transpired in between twice and 5 situations per year in the last 10 several years in metropolitan São Paulo, according to the authors.

The review was supported by São Paulo Research Foundation—FAPESP beneath the aegis of its Analysis System on Global Local weather Improve (RPGCC). The findings are claimed in the Annals of the New York Academy of Sciences.

Researchers affiliated with INMET, the Nationwide Area Study Institute (INPE) and the University of São Paulo’s Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG-USP) also took component in the research.

“Rigorous rainstorms lasting a several hrs with enormous amounts of water, as considerably as 80 mm or 100 mm, are no for a longer time sporadic events. They are going on more and more regularly,” José Antonio Marengo, a senior researcher at CEMADEN and principal investigator for the research, told.

The scientists analyzed data gathered by INMET’s temperature stations at IAG-USP and Santana Lookout in the northern part of the town. The examination showed an improve in the variety of times with significant rain and in the frequency of rainfall extremes, particularly through the rainy time (spring-summer season).

The dry season utilized to come about in between April and September in most of the point out but has lasted until finally Oct in modern a long time. The amount of consecutive days without having any rain at all has also progressively amplified, suggesting that weighty rainfall situations are concentrated in fewer times, interrupted by for a longer period intervals of warm dry climate.

With fewer cold nights and additional incredibly hot days, convective rainfall is more possible to arise, expanding the frequency and intensity of extraordinary rainfall, the authors take note.

In convective rainfall, the floor heats up, boosting evaporation and leading to heat moist air to increase (convection). As the air ascends, it cools and varieties convective clouds, which precipitate upon reaching saturation.

“We observed a prolonged-expression pattern in this type of climate event, with very robust symptoms that local weather adjust is in development,” Marengo stated.

Documents from the IAG-USP and Santana Lookout weather stations confirmed a four-fold enhance in the selection of times with rainfall exceeding 100 mm amongst 2000 and 2018 in contrast with people from the 1940s or 1960s.

Records from IAG-USP also showed an boost in full rainfall, in the frequency and intensity of heavy precipitation, and in the frequency of consecutive dry days in the interval 1931-2017.

“This implies that the maximize in complete rainfall in São Paulo in latest many years was owing to an raise in ‘heavy’ precipitation, concentrated in less times and with for a longer period dry spells in involving,” Marengo reported.

Leads to

In accordance to the scientists, the changing rainfall regime in metropolitan São Paulo may well be owing to normal local climate variability but may perhaps also be associated to world wide warming and escalating urbanization that has happened in particular in the last 40 decades, which has exacerbated the prevalence of city heat islands.

The expansion of urbanization has reworked the region’s beforehand exposed soil and Atlantic Rainforest remnants into sealed concrete, cement and asphalt surfaces that take in warmth whilst retaining no humidity. The temperature rises for the duration of the day, and as the sunshine goes down, the accrued heat rises into the atmosphere, the relative humidity falls, and water evaporates swiftly from the ground to sort towering cumulonimbus clouds, Marengo spelled out.

In his see, heat islands and comparable effects enable demonstrate the enhance in severe rainfall functions that occurred in metropolitan São Paulo amongst 1933 and 2010.

In the past 20 a long time, these adjustments in the rainfall regime, in conjunction with the substantial-chance design of properties on hillsides and riverbanks, have led to an raise in hydrometeorological hazards, triggering disasters this kind of as flash floods, river flooding and landslides, the authors take note.

“An excessive rainfall occasion just isn’t by itself a purely natural disaster. So-known as normal disasters truly result from a mix of factors ranging from weather and climate to urban, financial and social phenomena. In other words and phrases, they are also anthropogenic disasters that result from human action, not just weather,” Marengo mentioned.

Most Brazilian states endure from flooding, but it is worst in São Paulo, which accounts for 33.36% of conditions, adopted by Santa Catarina (11.25%), Rio Grande do Sul (9.06%), Paraná (8.33%), Rio de Janeiro (7.28%) and Minas Gerais (5.96%).

Some 170 river floods and flash floods transpired in the period of time 2014-18. Flash floods created the most deaths and serious accidents, adopted by landslides and mudslides.

“The Southeast and South locations of Brazil are the worst affected by hydrometeorological disasters simply because of their inhabitants density,” Marengo mentioned.

“Landslides, for case in point, only get rid of people today mainly because they are forced to stay in superior-hazard locations where by no just one ought to construct a household. The streets only fill up with water simply because the rivers have been channelized and buried, and the city’s surfaces are sealed with asphalt and concrete.”



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