The question is repeated every time we witness an extreme weather event: did this phenomenon happen naturally or is it a fact of climate change? The question was never answered, because it was wrong.
The association between climate change and extreme events — such as storms, floods, droughts, hurricanes or tornadoes — is more complex than a direct cause-and-effect relationship.
There would be no scientific basis for saying something like “this rain here was the fault of climate change, but that other one is natural and would have happened anyway”. Global warming influences the entire climate system without discrimination.
The correct question, which led scientists to find a clear relationship between different expressions of the same phenomenon, asks how rising global temperatures impact the frequency and intensity of extreme events.
The response was quantified in an unprecedented way in the latest IPCC report, the UN Intergovernmental Panel on Climate Change.
According to the global data of the report, heavy rains in the world are already 0.3 times more frequent and 6.7% more intense.
In an extreme scenario, with a 4°C increase in the global average temperature, precipitation could become 30.2% higher and the frequency —whose global average is one heavy rain per decade—could almost triple, reaching 2.7 occurrences in the same period.
More frequent and more intense than the standards for the period, the rains we have experienced in the last two months in municipalities in Bahia, Minas Gerais and São Paulo confirm a time frame defined, since the late 1980s, by IPCC reports.
They pointed to the year 2020 as the horizon for climate action, since from that year onwards the occurrence of extreme events would be more expressive.
“When the temperature increases, this puts more energy in the atmosphere. If there is a source of moisture, this generates more evaporation and makes the clouds grow more. Clouds with greater vertical development cause more intense rains”, describes doctor in Meteorology Gilvan Sampaio , coordinator of Earth Sciences at Inpe (National Institute for Space Research).
“The climate system today has much more energy to dissipate than it had 50 years ago. Major droughts and floods are ways of dissipating this energy”, says Paulo Artaxo, a physicist at USP and one of the authors of the IPCC’s scientific reports.
Although we have already experienced isolated episodes of intense rainfall in recent decades, with rainfall that exceeds the precipitation forecast for the whole month by just a few days, climate change has unprecedented patterns, for which we are not prepared.
“With heavier rains, risk areas will be expanded. Areas that historically do not flood may begin to suffer from floods. We need to map them”, highlights Ivan Maglio, a researcher at USP and a postdoctoral fellow in urban planning and climate change.
“It is not enough to address physical risks when there is an emergency, it is necessary to create climate adaptation plans to minimize these problems with prevention and preparedness”, he adds.
For at least a decade, the rulers of capitals such as São Paulo and Rio de Janeiro have had access to scientific information on regionally projected climate impacts.
Coordinated by Inpe in partnership with universities, the study “Megacities, Vulnerability and Climate Change” projected the impacts of global warming on the two cities by the end of the century.
“Total rainfall above 50 mm/day, practically non-existent before the 50s of the last century, commonly occurs two to five times a year in the city of São Paulo. The growing urbanization of the peripheries acting in synergy with global warming projects that events with large volumes of rainfall will occur more frequently in the future, encompassing an increasingly larger geographic area of the metropolitan region”, says the Inpe study published in 2010.
The study crossed the projections of urban expansion in the metropolitan region and the expansion of risk areas caused by increased rainfall. By 2030, more than 20% of the expansion area would be susceptible to flooding and flooding and about 11% to landslides.
Climate adaptation plans need to form an axis of urban planning, together with the fight against social inequality — since the most socially vulnerable populations are also the most impacted by climate change and form the majority of residents in risk areas.
This Wednesday (2), the weather warning map from Inmet (National Institute of Meteorology) points out “danger” or “potential danger” linked to intense rains in much of the country, covering the entire North, Midwest and Southeast regions.
Despite the photo of the moment pointing to rains, climate change should still increase the droughts, which also promise to be more intense and frequent.
Regional projections from the IPCC published last August show an increase in heavy rains in the Center-South of Brazil, with large volumes of water concentrated in up to five days of rain, while the Northeast and Amazon are expected to suffer from longer dry periods.
Without the usual rhythm and predictability, rain and drought can be equally synonymous with catastrophe.
In the early days of agriculture, the invention of the concept of time allowed humanity to deal with natural cycles. The challenge now resides especially in the lack of regularity of the times of nature, which requires reinforcement in the planning of medium and long-term public policies, based on the best available science. The only way out is to get ahead.
Source: Folha
