A study reported in Nature analyzed floods and droughts that affected the same place twice, finding that the second occurrence caused more damage, generally speaking. The authors included scientists affiliated with the University of São Paulo (photograph taken during the 2014 drought affecting the Cantareira system, which supplies water to some 9 million inhabitants of metropolitan São Paulo; credit: SABESP)
Published on 11/21/2022
By Luciana Constantino | Agência FAPESP – The impacts of extreme weather events have intensified in several countries, mainly owing to global warming. Researchers predict a doubling of economic losses due to flooding worldwide and a tripling of the losses due to drought in Europe and China if the average global temperature rises 2 °C above the pre-industrial level. Risk management policies to mitigate the effects of environmental disasters are increasingly important in this context.
A significant contribution to the discussion of disaster risk management comes from a study conducted by 91 scientists in several countries, including Brazil, and reported in a paper published in Nature. The group analyzed a series of climate events that occurred in recent decades around the world to show that risk management reduces vulnerability to flooding and drought but is relatively ineffective in limiting the impact of event sequences of unprecedented magnitude.
The study focused on 45 pairs of events that occurred in the same area on average 16 years apart between 1947 and 2019; 26 event pairs were floods and 19 were droughts. The events occurred across different socio-economic, hydrological and climate contexts on all continents.
One of the aims was to find out how risk factors changed between the first and second extreme episode, and to compare their impacts. According to the authors, where the second event was more intense than the first, its impacts were worse if risk management was based only on prior episodes and failed to plan for extreme cases such as rivers overflowing or levees and reservoirs bursting.
“Environmental risk management needs to be revisited and viewed as grounds for genuine improvement. The process is challenging but full of opportunities, not least in the case of Brazil,” Eduardo Mario Mendiondo, a co-author of the article, told Agência FAPESP.
Mendiondo is a professor at the Hydraulics and Sanitation Department of the University of São Paulo's São Carlos School of Engineering (EESC-USP) in Brazil, and a researcher affiliated with the National Institute of Science and Technology for Climate Change Phase 2 (INCT-MC2), which is supported by FAPESP. He is also a lead researcher at the Water Adaptive Design and Innovation Laboratory (WADILab) and works at two of USP’s research centers: the Interdisciplinary Climate Investigation Center (INCLINE) and the São Paulo State Disaster Research Center (CEPED).
The study was led by Heidi Kreibich, chair of a working group on flood risk and climate adaptation at the Potsdam Center for Research in Geosciences (GFZ) in Germany and a leader of Panta Rhei, a research initiative of the International Association of Hydrological Sciences (IAHS), a non-governmental scientific organization founded 100 years ago (in 1922). In the past decade, the initiative has built regional and international alliances in pursuit of an integrated, multidisciplinary and inclusive vision of the co-evolution of hydrologic and social systems, as exemplified by decentralized water supply facilities.
According to the article, the dataset included only two success stories, in the sense that the impacts of the second event were reduced despite increased hazard: a pair of floods due to heavy rain in Barcelona, Spain (1995 and 2018); and a pair of river floods in Germany and Austria (2012 and 2013). The main factors in common were institutional changes leading to improved governance of flood risk management, with more integration in the management of emergencies and early warning systems; and heavy investment in structural measures such as construction of rainwater reservoirs and levees.
Another positive point was interdisciplinarity in dealing with these issues and in research, potentially avoiding isolation of science or its use in silos without open dialogue. An example of interdisciplinary action is the use of new risk transfer instruments such as climate-risk insurance.
The authors note that according to international best practice, risk management aims to reduce the impact of events by modifying hazard, exposure and vulnerability. Hazard is a process or activity that may cause loss of life, injury or other health impacts, damage to property, social and economic disruption or environmental degradation. Exposure relates to people, infrastructure and other tangible assets located in hazard-prone areas. Vulnerability is determined by physical, social, economic and environmental factors that increase susceptibility to hazard.
All three risk drivers can be exacerbated by poor management and their impacts can be direct (e.g. deaths and monetary losses), indirect (e.g. disruption of traffic or tourism) and intangible (e.g. impacts on human health or cultural heritage). They are influenced by changes in population density and socio-economic development, and can be made worse by suboptimal implementation of non-structural measures such as risk-aware regional planning and early warning.
Decentralization and participatory management
In the case of Brazil, Mendiondo and other researchers at EESC-USP studied the water supply system in metropolitan São Paulo (the largest metropolitan area in the southern hemisphere, with 22 million inhabitants), including the Upper Tietê and Cantareira sections. “The rivers in this region aren’t as large as those of other regions, like the Amazon, but the system is important because of the large population it serves, involving synergies among various sectors. The innovative approach we used in the study promotes decentralized, participatory and long-term solutions,” Mendiondo said.
In São Paulo, construction of reservoirs to mitigate the impact of drought is fundamental to water security, he added, but success depends on permanent education and science diffusion campaigns to encourage rational water consumption and reuse.
“The scientific evidence proves that if secure and decentralized rainwater reuse in metropolitan São Paulo had been planned for in the last 40 years, it would have been possible to live with the three great droughts of the twenty-first century without the need to build or expand large reservoirs and without water rationing in neighborhoods,” Mendiondo said. “Climate isn’t the only driver. The type of planning prioritized is also a key factor. Water and society should co-evolve. Without cultural awareness and [cultivation of] better habits, building more reservoirs could even lead to increased water consumption, heightening the risk of future water shortages and fueling a vicious circle of water insecurity. This is happening right now in California [USA] and Shanghai [China].”
For the sake of exemplification, Mendiondo cited another paper published in February 2022, which compared droughts occurring in metropolitan São Paulo in 1985-86 and 2013-15 (the latter more extreme than the former), and showed that the region was made more vulnerable by delays in implementing the decentralized rainwater reuse required by public policy and dependence on too few reservoirs. The authors included PhD candidate Felipe Arguello de Souza and EESC-USP alumni Guilherme Mohor and Diego Guzmán, all of whom are co-authors of the paper published recently in Nature.
The article “The challenge of unprecedented floods and droughts in risk management” is at: www.nature.com/articles/s41586-022-04917-5.