The alarm bells
The mega study relies on 11 climate models for the first time to project global flood risk for the end of this century when the climate is predicted to get warmer. Through a state-of-the-art global river routing model (called the Catchment-based Macro-scale Floodplain Model or CaMa-Flood), Japanese and British scientists have demonstrated a large increase in flood frequency in Southeast Asia, peninsular India, eastern Africa and the northern half of the Andes.
Lead researcher Yukiko Hirabayashi from the Institute of Engineering Innovation at The University of Tokyo says the team looked at changes in flooding and evaluated its consistency and spread. Their study predicts a large increase in flood frequency in parts of Asia, Africa and South America in response to future warming conditions. These findings suggest that there is a necessity for adaptation to intensified floods and the introduction of further strategies to mitigate greenhouse gas emissions, Hirabayashi says.
However, the study also projects a decrease in flood frequency in certain areas of the world — northern and Eastern Europe, Anatolia, Central Asia, central North America and southern South America.
In addition to the global-scale analysis, the models were studied at the outlets of selected river basins. The models suggest that during the 21st century, the frequency of floods will increase in almost all of the selected rivers in South Asia, Southeast Asia, Oceania, Africa and Northeast Eurasia. They also project that the 20th century 100-year flood event will occur about every 10–50 years in many of these rivers in the 21st century.
The authors caution that global exposure to floods would increase depending on the degree of warming, but interannual variability of the exposure may imply the necessity of adaptation before significant warming. They highlight that major attention should be paid to adaptation and mitigation strategies in lower-latitude countries where flood frequency and population are both projected to increase.
Analysing the danger
Hirabayashi’s co-researcher Shinjiro Kanae from the Department of Civil Engineering at the Tokyo Institute of Technology says according to the summary of the IPCC special report SREX (2012) on the projection of future floods the “projected precipitation and temperature changes imply possible changes in floods, although overall there is low confidence in projections of changes in fluvial floods. Confidence is low due to limited evidence and because the causes of regional changes are complex….”
Kanae, who was involved in the writing the SREX summary, says the evidence was pretty limited when it was written last year but their new projection increases the level of evidence to a higher level.
“The so-called warm, humid regions (including Southeast Asia, East Asia, South Asia and tropical Africa) are already notoriously flood-prone. Unfortunately, many countries in these regions are developing. Also, population is likely to increase in some or many of them according to UN estimates. It’s a really ‘damp prospect’ for them,” he says.
Rajiv Sinha, professor of geosciences in the department of civil engineering at IIT Kanpur, says climate change can involve marked changes in the probability distribution of weather parameters (temperature and precipitation) and is likely to modify the magnitude-frequency relationship of the geomorphic processes.
“A series of unprecedented floods in several parts of India should force us to think that extreme events can and do occur. They should trigger serious thought that natural as well as anthropogenic forces are often not easy to separate,” Sinha says. He says some recent floods in India — Himachal Pradesh (July 2010), Leh (August 2010), several parts of Karnataka, Tamil Nadu, Andhra Pradesh and south Orissa during November-December 2010 — should serve as an indicator to a modified hydrological regime.
Globally too, severe floods in east China (May 2010); Rio Lorogo, Brazil (June 2010); Pakistan (August 2010) and Queensland, Australia (December 2010); Rio de Janeiro, Brazil (January, 2011); and Queensland, Australia (February, 2011) point towards this, he says.
Scientific analysis of archived data and model-simulated precipitation fields show that there is some increase in extreme rainfall events of high intensity and short duration rainfall in the last 50 years or so, according to Sushil Kumar Dash, head of the Centre for Atmospheric Sciences at IIT Delhi. “Such incidents are also likely to occur more in the future. These extreme rainfall incidents will most probably increase the chances of more flash floods and urban flooding in India,” he says.
Dash says atmospheric warming has impact on snow melting. The water level of the three most important rivers of India may remain higher in summer due to increased snow melting and this might lead to more flooding, he adds.
Science versus policy
But dependence on scientific studies to steer policy in South Asia is virtually nil, says Mashfiqus Salehin, a professor at the Institute of Water and Flood Management (IWFM) in Dhaka-based Bangladesh University of Engineering and Technology. “We have extremely ill planned, ad-hoc and temporary flood control projects — thousands of kilometres of embankments get breached every year.” Bangladesh’s mighty braided river Jamuna has close to 13,000 hectares of embankments, which are breached regularly due to increase in extreme flood events in recent times.
Salehin says 68 per cent of the Ganga-Bramhaputra-Meghna basin lies in Assam, West Bengal, Bihar and Uttar Pradesh states of India. The Ganges has a very high damage potential, especially in Uttar Pradesh and Bihar, he cautions.
Assam’s Bramhaputra valley represents one of the most acutely hazard-prone regions in India having a total flood-prone area of 3.2 mega hectares. It is time the flood-prone countries in south Asia learnt from flood management experience and basin level integration from one another. “For instance, Bangladesh needs knowledge on the effect of hydel projects in India and China since those very rivers come to this country. But sadly, there’s no clarity on trans-boundary water cooperation between the countries,” Salehin points out.
He cites the example of the barrages over river Teesta constructed on either side of the Indo-Bangladesh border without bilateral consultation. The joint river commission between India and Bangladesh has also not been very conclusive in its long years of discourse, he points out.
In fact, in 2008, the Indo-Bangladesh Joint River Commission had rued the lack of information between the two countries and poor availability of rainfall data across borders, says Istiak Sobhan, Programme Coordinator of the IUCN Bangladesh country office. “Ironically, India and Bangladesh rely more on US satellite maps for flood impact assessment rather than data from one another,” he points out. Flood forecasting, therefore, becomes very problematic for Bangladesh since real time data from upstream Meghalaya and Assam is not available, especially during flash floods.
Sobhan says hydrogeological changes along this stretch also determine the flood intensity and frequency but data on this is also largely insufficient.
Power play and water politics
The heightened risk of flooding in south Asia can only be tackled if countries press for a common south Asia charter on water, something like the SAARC charter of democracy, says Imtiaz Ahmed, professor of international relations at the University of Dhaka. “The issue across south Asia is that it is very easy to be a nationalist but very difficult to be a south Asian,” he points out. Ahmed says water politics has traditionally been governed by territoriality, colonised ‘developmentality’ and a nationalised identity of water.
“That is not going to work in favour of nations in the new paradigm that predicts worse flooding scenario in south Asia,” Ahmed says.
Rohan D’souza, an assistant professor at Delhi-based Jawaharlal Nehru University’s Centre for Studies in Science Policy says in South Asia, flood control has traditionally been given ‘structural engineering’ responses, such as large dams and embankments. “The belief was that a river’s flow could either be stored in huge reservoirs or kept firmly contained within its channel by having the banks walled on both sides.” This approach has been replaced in recent years by flood management policies that involve tactical retreats from the river bed to some structural engineering efforts that can contain the river.
Analysing the subcontinent’s vulnerability, he says South Asia lives with the dramatic changes brought about by its many colonial hydraulic legacies. “Throughout the latter half of the 20th century, flood control has often been the immediate and central response of the governments to recurring floods. The long history and the complex collection of practices for flood utilization — be it in the form of cropping strategies, unique plant varieties and even prudent location strategies — has been forgotten and deleted from the memory of official water management policies,” he rues.
D’souza echoes Ahmed’s demand for a regional water charter. “I entirely subscribe to the idea of a south Asia water charter. It is the need of the hour.”
- Hirabayashi, Y. et al. Global flood risk under climate change. Nat. Climate Change. (2013) doi: 10.1038/NCLIMATE1911