Intense rains in São Paulo and drought in the USA corroborate IPCC conclusion

Scientists make this assessment based on the most recent report published by the Intergovernmental Panel on Climate Change

By Elton Alisson

Agência FAPESP – Despite the need for more studies to reiterate the evidence and clarify several uncertainties in the confidence level of some forecasts, the conclusion of the Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX) is corroborated by the greater frequency of extreme climate events in various regions of the world, such as the current drought in the United States, and by the increase in expenditure over the past few years by countries such as Brazil to deal with losses incurred as a result of flooding and landslides caused by intense rain.

This is the conclusion of researchers participating in the workshop “Risk Management for Extreme Climate and Disasters in Central and South America: What Can We Learn from the IPCC Special Report on SREX Extremes?”, held August 15 – 16 in São Paulo.

The workshop was sponsored by FAPESP and by the National Institute for Space Research (Inpe) in partnership with the IPCC and the Climate and Development Knowledge Network (CDKN), both of the United Kingdom, through support from Norway’s Ministry of Foreign Affairs and Climate and Pollution Agency. The objective of the event was to debate the conclusions of the SREX report and the options for managing the impacts of climate extremes, especially in South and Central America.

One of the main conclusions of the report, penned by the IPCC at the request of the Norwegian government and the UN International Strategy for Disaster Reduction, is that climate extremes have been increasing in frequency around the world during the past few decades as a result of climate change.

Consequently, the socioeconomic impacts of these phenomena have also increased in the past few years because of the human population’s greater vulnerability and exposure to them as a result of factors such as the substantial increase in urbanization in regions such as South America.

However, the researchers state, that there are uncertainties, owing to the scarcity of data, about the tendency of extreme climate events to occur on a global scale.

The report indicates, for example, that an increase in the frequency of hot days and nights is very probable over the next few years in various regions of the planet, a trend that that has already been detected in meteorological observations in most regions of southern and southwestern Brazil and in the southeast of South America.

In contrast, the report identifies doubts about an increase in the frequency of intense rains worldwide, indicating regions that have shown an increase and others where there has been a decrease. In view of these findings, it is impossible to generalize a conclusion that intense rains occur more frequently.

Nevertheless, the more frequent torrential rains in São Paulo over the past few decades indicate that stronger rain precipitation has occurred, at least on a regional scale.

“If there are still uncertainties about the trend toward increased rain frequency on a global scale, in São Paulo’s case there is no doubt that intense rains have increased significantly in the city in the past 50 to 70 years,” comments Carlos Nobre, secretary of Policy and Research and Development Programs at the Ministry of Science Technology and Innovation, a member of the coordination team for the FAPESP Program for Global Climate Change, an IPCC member and one of the authors of the SREX report.

“Today, intense rain that causes flooding and disasters in São Paulo is three times more frequent than it was 70 years ago. And the increased frequency of this type of extreme climate event in the São Paulo capital is very well documented,” affirms Nobre.

Because there is concrete and consistent proof of the increase in the frequency of intense rains in São Paulo in the past decades, according to Nobre, the city can serve as an excellent laboratory for conducting studies on the socioeconomic impacts of the increased frequency of extreme climate events, in terms of the level of exposure and the vulnerability of populations to these events. This evidence will serves as a means of confirming the IPCC’s conclusions.

“I would be very interested in conducting studies to quantify the enormous climate changes in São Paulo caused by the impact of urbanization and the effect of the urban heat island in the city,” states Nobre.

Socioeconomic impacts

Nobre cited a few examples of studies published recently by researchers in São Paulo State that outline the increased risks to the population caused by the greater frequency of intense rain.

One of the studies indicated an increase in areas in the São Paulo capital territory that are susceptible to flooding and are at a higher risk of landslides. Another study showed that with urbanization, the areas of intense rain expanded and increased the risk of leptospirosis, a disease transmitted by rat urine.

A study conducted by the Ecology Department at the Universidade Estadual Paulista (Unesp) Rio Claro campus, in partnership with Inpe, identified Campinas and Ribeirão Preto as two regions in São Paulo State that will be more vulnerable to climate change in the coming decades.

The major population concentration in Campinas increases the severity of the potential impacts associated with a flood. Ribeirão Preto is also populous. It too is likely to experience Brazil’s highest temperatures in the coming decades.

“We can discern the socioeconomic impacts on some regions caused by the acceleration of extreme climate events. These impacts are associated with the greater vulnerability of populations given the greater urbanization of the world and, in particular, of cities in Latin America, where this process has occurred in the past few decades in a chaotic manner,” says Nobre.

According to Nobre, in Brazil, for example, the resources for the reconstruction of regions affected by disasters resulting from extreme climate events have evolved very rapidly during the past 10 years and exceeded R$ 1.6 billion in 2011. “The economic impact of the disasters caused by extreme climate events is already significant in the country,” he affirms.

One of the examples given by researchers to illustrate the increased frequency of extreme climate events in Brazil in the past few years is the low humidity currently recorded in the country’s midwest and São Paulo’s southeast, in addition to the constant rains in the summer in São Paulo, Rio de Janeiro and other regions in the west and droughts in the western Amazon.

Outside Brazil, the drought currently affecting the United States is viewed by researchers as an example of an extreme climate event of uncommon magnitude that corroborates the conclusions of the SREX report.

“It is a climate event that occurs perhaps only once in 100 years and has an enormous economic and social impact, as it perturbs the entire agricultural commodity pricing system and also affects food security,” comments Nobre.

According to Nobre, the drought in the United States was not documented in SREX and should be included in the IPCC’s next report, slated for publication in 2013. This report should clarify the uncertainties in the level of confidence of some forecasts noted in the current document.

“Much of the information published in the SREX will be updated in the fifth IPCC report, through which we hope to gain a better comprehension of extreme climate events,” said José Marengo, researcher at Inpe’s Earth System Science Center (CCST), an IPCC member and one of the authors of SREX.

The lectures given at the workshop “Risk Management for Extreme Climate and Disasters in Central and South America: What Can We Learn from the IPCC Special Report on SREX Extremes?” are available at www.fapesp.br/ipccsrex/program.