February 20, 2026
NEWSLETTER
Flooded cities: When rain was only part of the problem
In this February newsletter, we look beyond rainfall totals and examine how recent flood events in Spain and France reveal a more complex reality: extreme precipitation is often only the trigger, while evolving ground conditions determine the scale of impact. By exploring the interaction between intense rainfall, land deformation, and infrastructure vulnerability — and the role of satellite-based monitoring — we highlight why understanding the ground beneath our cities is becoming essential for climate resilience.
Over the past year, Mediterranean Spain and parts of southern France have experienced severe flood episodes, including the 2024 and 2025 DANA (Depresión Aislada en Niveles Altos) events. Torrential rainfall overwhelmed drainage systems within hours. Railway services in Catalonia were interrupted. Urban streets were submerged. Transport corridors and logistics networks faced temporary paralysis. The immediate explanation pointed to exceptional meteorological intensity — and indeed, rainfall records were broken in several locations. Yet rainfall alone does not fully explain the disruption observed.
In early 2026, a commuter train near Gelida in Catalonia derailed after a retaining wall collapsed onto the track during a period of intense and prolonged rainfall. The incident was not linked to a DANA episode but to sustained precipitation that saturated the ground and increased pressure behind the structure. As pore water pressure rose and soil strength declined, stability margins were reduced until failure occurred. Rainfall was the trigger — yet vulnerability had been building over time.
Flood events are frequently described as hydraulic crises, but their consequences often emerge through geotechnical mechanisms. When soils become saturated, effective stress decreases and shear strength is reduced. Soil stiffness changes. Bearing capacity declines. Rail embankments, road foundations, and retaining systems are particularly sensitive to these variations, and performance can deteriorate rapidly once critical saturation thresholds are exceeded.
The DANA episodes of 2024 and 2025 demonstrated how quickly Mediterranean rainfall can escalate into widespread flooding. High-intensity precipitation overwhelm drainage networks and expose infrastructure to sudden stress. Although not every disruption was directly caused by a DANA system, extreme rainfall events — whether classified as DANA or not — amplify existing vulnerabilities.
Repeated saturation cycles progressively modify soil structure. Fine-grained soils consolidate under cyclic wetting. Granular materials may experience internal erosion. Drainage patterns shift. Minor deformation accumulates over time. Each storm adds to the stress history rather than resetting the system, and infrastructure networks may not have been designed for increasingly volatile saturation cycles.
Long-term land deformation acts as a silent risk multiplier. Millimeter-scale vertical movement may appear negligible annually, yet over a decade it can amount to several centimeters of elevation change. In flood-prone environments, even subtle subsidence can reduce drainage gradients, increase ponding duration, expand low-lying zones, and alter hydraulic behavior. Rainfall then interacts with a surface that no longer behaves as originally designed.
This interaction between extreme precipitation and long-term deformation is frequently overlooked in flood risk discussions. Yet it may help explain why certain corridors repeatedly experience disruption while others remain stable under similar rainfall conditions.
This is where wide-area deformation monitoring becomes essential. Satellite-based Interferometric Synthetic Aperture Radar (InSAR) enables detection of millimeter-scale ground movement across entire regions. While rainfall forecasting indicates when extreme weather may occur, deformation monitoring reveals how the ground beneath infrastructure has been evolving over time.
GeoKinesia applies InSAR technology to monitor progressive subsidence, differential settlement, and embankment deformation across transport corridors and urban environments. In flood-prone regions, this provides an additional layer of situational awareness. Areas experiencing gradual elevation change can be identified before the next storm arrives, and infrastructure corridors under cumulative stress can be monitored continuously rather than inspected only after disruption occurs.
Following a flood event, InSAR can also support rapid assessment of newly activated deformation hotspots, helping prioritize inspections and repair. This dual capability — prevention and post-event evaluation — strengthens both phases of the civil protection cycle and supports more informed decision-making. Extreme climate events such as flooding and flash floods represent recurrent hazards in Mediterranean Spain but also in many regions of the world. Their intensity and frequency are expected to grow due to climate change, increasing risks to human safety, critical infrastructure, and economic stability. Addressing these risks requires integrating hydrological forecasting with continuous geohazard monitoring.
Effective flood risk management must address both the Prevention and Emergency Response phases of the civil protection cycle. During the prevention phase, continuous ground deformation monitoring helps identify progressive subsidence, differential settlement, and embankment instability before failure occurs, allowing proactive mitigation. During emergency response, rapid post-event deformation assessment supports prioritization of inspections, resource allocation, and infrastructure reopening decisions. Integrating wide-area InSAR monitoring into both phases strengthens preparedness while improving operational response when extreme rainfall events occur.
Flood resilience is no longer solely about managing water. It is about understanding how water interacts with the ground — and how the ground, in turn, supports the systems upon which society depends.
Rain may trigger the event. Ground behavior often shapes its consequences. In many recent European flood episodes, rain was only part of the problem.
