From April 14 to 19, 2024, the General Assembly of the European Geosciences Union (EGU) took place in Vienna, Austria. Anne Van Loon, Marlies Barendrecht, and Alessia Matano represented the PerfectSTORM research group, presenting their work on the complex relationships between drought and flooding.

On the Drought-Flood Conundrum: Do Droughts Cause More or Less Flooding?

Anne gave a keynote presentation exploring whether drought leads to more or less flooding. This conundrum is rooted in two contrasting hydrological theories:

• Subsurface Hydrology: Studies suggest that dry prior conditions result in greater storage capacity in the soil, reducing flood peaks.
• Surface Hydrology: Studies claim that dry, hydrophobic soils reduce infiltration and increase surface runoff, leading to higher flood peaks.

Anne’s presentation, based on scientific literature, global data, qualitative case studies, and media reports, explored these opposing views. She highlighted the importance of integrating hydrological processes with meteorological and anthropogenic aspects to fully understand the dynamics of drought-flood events. The presentation was based on the paper by Marlies and the PerfectSTORM team, published earlier this year (Barendrecht et al., 2024, WIRES Water, Exploring drought-to-flood interactions and dynamics: A global case review;  https://wires.onlinelibrary.wiley.com/doi/full/10.1002/wat2.1726), and ongoing work of Alessia, Ruben and Heidi.  

Investigating Human-Water Dynamics Leading to Increased Drought and Flood Risk in Kitui, Kenya

Marlies presented research on Kitui County, Kenya, a region plagued by severe drought and periodic flooding. This research focused on understanding the interplay between climatic and human factors that cause drought and flood risks.

She presented the ongoing development of a system dynamics model that takes into account human adaptation to drought and floods. With the model we investigate how changing environmental conditions and the adaptation and coping responses influence water and food security. The model may be used to provide further insights into potential policies and measures to mitigate future risks.

Drought Influences on Hydrological Regimes

Alessia presented an analysis of how persistent drought conditions impact catchment responses to precipitation. The study used an extensive dataset comprising observations and remote sensing data of streamflow, precipitation, soil moisture, and total water storage from 5590 catchments worldwide.

Through multivariate statistical analysis and step-change analyses fluctuations and abrupt shifts in the precipitation-streamflow relationship during and after drought periods were detected and the influence of drought type and severity on these changes was investigated.

The study revealed that drought conditions lead to significantly lower streamflow than expected during and up to one year after the drought conditions, while only vegetation anomalies result in general to an increase of streamflow. This is more pronounced in arid, warm-temperate, and equatorial regions, whereas snow regions exhibit greater resilience. Identified shifts in the precipitation-streamflow relationship showed both increase and decrease in streamflow sensitivity to precipitation. These step changes align with periods of severe drought, that propagate through the hydrological system and persist over years for positive steps.

The study shed light on the importance of considering regional characteristics in predicting dynamic catchment response to precipitation under and after persistent drought conditions.

Conclusion

PerfectSTORM’s contributions at the EGU Conference 2024 offered insights into the complex dynamics between drought and flooding. The presented research highlighted the importance of integrating hydrological, meteorological, and human factors to develop strategies for managing water risks in a changing climate. These findings provide contributions for policymakers, further research, and practitioners working on sustainable water management solutions.