We spoke to Marc Lennartz, a PhD researcher at the GFZ Helmholtz Centre for Geosciences, who is conducting his research “Understanding and preparing for High‑Impact‑Low‑Probability flood events” within the scope of our programme. In this interview, we discussed how his work seeks to improve preparedness for rare but devastating extreme floods, the importance of developing robust stress‑test frameworks, and the opportunities and challenges of working across transboundary river systems.
Can you briefly describe the main topic of your PhD research?
My research focuses on understanding and preparing for High-Impact-Low-Probability (HILP) flood events. These are exceptionally rare floods which can expose uniquely vulnerabilities in our disaster management system, as demonstrated by the July 2021 floods in Central Europe. Climate change has the potential to amplify events, like the July 2021 floods in central Europe. Due to their rarity, and due to the destabilizing effect of climate change, the processes behind HILP floods are not yet well understood. My PhD aims to help close this knowledge gap.
What motivated you to pursue a PhD, and why in this field of research?
To me, the most exciting part of research is tackling broader societal problems in a comprehensive and interdisciplinary way. Incidentally, preparing for extreme floods demands collaboration across diverse fields of research, as well as close interaction with practitioners and policy-makers. This field allows me to study many components of the human-water system in depth while keeping the large picture in mind.
Does your research focus on a specific geographic area?
While the methods I develop should be broadly applicable, vulnerabilities to extreme floods vary significantly between regions. Therefore, a key component of my work is the development of localised flood stress tests. Within the JCAR ATRACE project, we are collaborating on a regional stress test in the Roer river catchment, which will serve as a case study in preparing for HILP events.
What specific objectives are you aiming to achieve with your current research?
As a first step, I will systematically review the current state of the art in HILP flood stress testing. This includes all studies that simulate very extreme rainfall-induced flooding and evaluate societal impacts. This review will highlight which important damage-driving processes are missing in current stress-test frameworks. Based on this, I will develop improved stress tests for unprecedented floods and apply these methods to regional case studies.
How does your work fit within the JCAR ATRACE programme and its goals?
The JCAR ATRACE programme is involved in several transboundary stress tests, which include very extreme rainfall scenarios. My research aims to make these studies more methodologically robust and more relevant for people living in flood-prone areas. By directly participating in the JCAR ATRACE stress tests I am in a great position to gain new scientific insight and to put them into practice immediately. This will support the JCAR ATRACE mission of achieving better flood preparedness.
Which opportunities and challenges do you envision conducting your research in a transboundary context?
Working with very rare floods often means dealing with inadequate data. In transboundary catchments this can be exacerbated when data collection differs across regions. At the same time, transboundary systems often feature a wider variety of prevention and adaptation measures. This presents a valuable opportunity to compare the effectiveness of different strategies, particularly during the July 2021 floods.
How does your research fit within the partnerships between regional governments and academic institutions?
Preparing for HILP floods, and for flooding more generally, is typically a collaborative process between governments and academic institutions. By providing a clear guide on stress testing very extreme floods, I aim to improve communication between stakeholders and support more consistent, higher-quality analyses.
In which ways do you see your research having an impact on policymaking?
Currently, few policies exist with an explicitly focus on floods exceeding return levels of 100 years. My goal is to provide a clear overview and practical guidelines for incorporating such unprecedented events into planning and policy. Ideally, this will contribute to the development of new strategies that enhance long-term flood preparedness.
Given the wide variety of stakeholders involved in JCAR ATRACE, what interactions do you look forward to?
The impacts of the July 2021 floods were often exacerbated or dampened by unique local conditions. Often the characteristics only become apparent when talking to local experts. I particularly look forward to working with regional water, which have a great understanding how impacts have been, or could have been, mitigated.
What long-term impacts do you envision your research having on regional climate strategies?
I aim to make preparation for HILP floods more accessible by developing stress tests that are transparent and easy to reproduce. By clearly outlining uncertainties and risks, regional stakeholders can make more informed decisions as hydrological extremes evolve under climate change.
Which scientific or technological breakthroughs do you hope to encounter during your PhD?
Ideally, my research will facility easy detection of bottlenecks, which could amplify impacts during an extreme flood. By showing how sensitive impacts are to different system components, stake holders will be better able to identify suitable adaptation measures.
What are some challenges you anticipate facing as climate conditions continue to change? And how do you see your research adapting to these evolving challenges?
Climate change not only alters which extreme events are possible, but also increases the likelihood of devastating floods. The inherent uncertainties make it difficult for communities to prepare adequately. By developing robust risk-assessment frameworks, my research aims to help communities adapt more effectively despite these uncertainties.
