As a WiSER ('Women Involvement in Science and Engineering Research') awardee, Dr Poulami Ganguli plans to develop a probability-based method for identifying flood hotspots and associated hazards, especially successive extreme heatwaves and short-duration heavy rainfall events. In the interview, she tells us more about the topic and her project, which she is carrying out in cooperation with the GFZ German Research Centre for Geosciences.

Dr Ganguli, the aim of your project is to develop a probability-based tool to identify compound flooding hotspots and associated hazards. If you achieve all your project goals in the upcoming years, what changes in forecasting of floods might this bring to your country?

Dr. Poulomi Ganguli: Our current project aims to develop a compound flood hazard framework resulting from sequential hazards due to humid heat stress and extreme rainfall and investigate their potential drivers. So far, most urban pluvial (rain-driven) flood risk assessment models in India consider hazards due to a single driver, i.e., heavy rainfall that causes overland flow and then floods. Therefore, this study aims to develop a climate-informed pluvial flood risk assessment model in a probabilistic framework. The developed model will identify urban settlements where sequential hazards, heat stress-extreme rainfall is persistent problem, and inform stakeholders and city administrators to update the design standards of existing hydraulic structures. Further, the derived insights are not limited to flood adaptation and mitigation measures; the research helps identify areas and urban settlements vulnerable to sequential climate hazards and heat stress-heavy rainfall. The hope is that government and other organizations can use this information to enhance the predictability of short-duration extreme rainfall and associated hazards and help to develop resilience-targeted adaptation strategies.

An important aspect of your work is the relation between the occurrences of extreme heat stress and heavy rainfall events. Could you tell us more about the links of such extreme events? How will you improve the calculation of probabilities?

With global climate change, sequential hazards, such as heatwaves and extreme rainfall, have become more frequent and severe. Extreme heat can drive atmospheric instability, leading to convective development and heavy rainfall. High heat and heavy rainfall might not be dangerous in isolation. However, a rapid and sequential occurrence of 'hot-wet' compound hazards may lead to catastrophic consequences due to the low recovery time between the two hazards. Severe heat stress can lead to heat-related illness, loss of labor productivity, and even mortality; they threaten power grids when air conditioning is required the most. Further, large floods can cause inundation of small urban watersheds, leading to critical infrastructural failures. Examples include severe heatwaves over India in late 1998, resulting in more than 2500 casualties. Within two weeks of the heatwave was followed by tropical cyclone-induced storms, followed by extreme rain, impacting over 4.6 Million people. Likewise, in 2019, Queensland, Australia, recently experienced sequential heat wave-flooding hazards that have caused over $1.2 billion US in economic losses. While the conventional risk assessment framework considers hazards from a single driver only, e.g., extreme precipitation-induced flooding, a multivariate probabilistic hazard framework considering heatwaves/extreme temperature and its associated characteristics as potential covariate(s) for heavy rainfall remains poorly understood. Here we aim to develop a suite of probabilistic tools that can capture the nonlinear interactions between interrelated drivers, impacting heatwave-extreme rainfall events, and improve the predictability of rare precipitation events in a warming climate. The insights from this study and developed probabilistic models can enhance real-time urban flood nowcasting and improve early warning.   

What was particularly important in the start-up phase of your project?

The crucial part of the project lies in the collection of hydrometric observations and an understanding of multivariate probability-based tools. While the collection of long-term observations is particularly challenging, especially for developing countries such as India, an adequate knowledge of probabilistic tools is necessary for investigating the cumulative impact of compound extremes. The reason is that such events involve combinations of several variables act interdependently, which has a more significant effect as compared to when each of these hazards occurs in isolation.   

Is there any advice that you, as an award winner, can already give to other scientists who manage their own projects? What skills - apart from the ones specific to your research field - are particularly needed?

One piece of advice could be to do a though background check regarding the problem definition and focus on the research problem that has a scope to inform societal challenges and has practical implications that support real-world problem-solving.

What are the next steps for you and your project?

Extreme hydrologic events, such as sequential hazards, have become near the norm in changing climates. For example, Europe experienced a record-breaking summer in 2021, leading to intense and prolonged heatwave in July-August in the Mediterranean region. Interestingly, this was accompanied by severe flooding in Western Europe due to heavy rainfall. The project's primary objective is evaluating compound hazard potentials of sequential 'hot-wet and/or dry' hazards across hotspot locations, where heatwaves are particularly of concern. While using a few selected locations, we are developing our probabilistic model; as a next step, we plan to expand our work across different climate regions. Finally, the output will be communicated to scientific venues through publications. The specific insights drawn from the project would inform stakeholders and city administrators to adapt such back-to-back natural hazards and develop mitigation policies. 

How did your former work at GFZ influence your current work in India concerning the way to do research but also the topics that you are working on? In what way will you continue to collaborate with GFZ colleagues?

The experience as a researcher at GFZ is quite enriching regarding skill development and expanding the research horizon away from the comfort zone. The experience gained at GFZ in due course of research helped to shape research proposals, develop tools and new methods, and develop collaborations across Europe. It also helps me diversify my research area, enabling me to work on different forms of natural hazards, from droughts to floods and, recently, compound extremes. In the future, I wish to continue collaborating with GFZ in developing a large-scale distributed hydrologic model chain for India, which we currently lack. 

You are currently working as assistant professor in your home country, India. You work in the Agricultural and Food Engineering department at IIT Kharagpur. How does working/lecturing in India differ from similar experiences in Europe?

Being a student in two different IITs (first as a master’s student at IIT Kharagpur and then a Ph.D. student at IIT Bombay) and now as an employee after years of postdoctoral research experience in three different countries, the USA, Canada, and last one in Germany, I can say that working environment in IITs is not very different from elsewhere globally. Thanks to generous support from the Government and a rich alumna pool, we have most of the computational research facilities available. At the same time, as a researcher, securing external grants to sustain research is also quite competitive and challenging. Unlike in Europe, the funded research project length is typically short and can be a maximum of three years or even less.

What role does outreach play, how important does it seem to you in the project context?

Compound climate and weather hazards involve multiple drivers contributing to risk, often resulting in amplified societal impact. The recent project aims at the sequential natural hazards due to heat stress and extreme rainfall and the identification of vulnerable urban settlements. While an increasing trend in heat waves is apparent globally due to global warming, low and middle-income countries, especially in tropical regions, are particularly at risk. Further, extreme rainfall and subsequent flooding, followed by a heatwave, has devastating consequences. The derived insights can help to develop policy recommendations in urban settlements to mitigate the risk of such hazards. This can enhance the cooperation between researchers and practitioners to adapt and develop climate-informed risk management strategies

Dr. Poulomi Ganguli, thank you very much for the interview!

About

Dr. Poulami Ganguli received her Ph.D. in Water Resources Engineering from the Department of Civil Engineering, IIT Bombay, in 2013. Her research interest lies at the intersection between hydrology and climate extremes, with a specific interest in the statistical modelling of extreme events. She received the prestigious Alexander von Humboldt early career research fellowship in 2017. Funded by this award, she worked as a scientist in Section Hydrology GFZ Potsdam for nearly two years focusing on compound flood hazard modelling over the pan-European domain. As a Women in Science and Engineering Research (WiSER) awardee, she plans to develop a probability-based tool to identify compound flooding hotspots and associated hazards due to the sequential occurrences of extreme heat stress-heavy rainfall events in collaboration with the host institute GFZ Potsdam.

References:

• Copernicus Climate Change Service (2022). Europe experienced its warmest summer on record in 2021, accompanied by severe floods in western Europe and dry conditions in the Mediterranean. Available at: climate.copernicus.eu/europe-experienced-its-warmest-summer-record-2021-accompanied-severe-floods-western-europe-and-dry (accessed June 14, 2023).
• EM-DAT. (2023). The international disasters database 2023. www.emdat.be (accessed June 20, 2023).
• Zhang W, Villarini G. (2020). Deadly compound heat stress-flooding hazard across the central United States. Geophys Res Lett; 47:e2020GL089185.