An increase in rainfall does not by itself mean water security has improved. How much of the falling water becomes groundwater potential, and how much leaves the system as surface runoff and evapotranspiration, is decided by the topography, geology and land cover of the region. Alkazar assesses flood, flash-flood and groundwater risk at both catchment and parcel scale through a process-based approach that goes beyond the headline rainfall figure.
In short: flood and groundwater risk analysis quantifies the flood and water-stress exposure of a parcel or a catchment by modelling how rainfall is partitioned between infiltration, surface runoff and evapotranspiration, together with topography, geology and land-cover data. The outputs can be used for site prioritisation and for physical climate risk reporting.
When is it needed?
- When flood or water risk has to be assessed before site selection or acquisition
- When flood risk needs to be quantified as part of physical climate risk reporting
- When the exposure of basements, infrastructure or critical equipment to flooding is questioned
- When it has to be understood what a rainfall increase in a region actually means for groundwater and water resources
Method: a process-based assessment
Rainfall is only an input to the hydrological system. How much of it turns into groundwater potential is determined by physical filters: the topography, the geological structure and the land cover of the region. Part of the falling water leaves as surface runoff, part returns to the atmosphere through evapotranspiration, and only where specific geological and topographic conditions are met does water infiltrate and build storage potential. Two catchments receiving exactly the same rainfall can therefore behave in completely different ways.
Our approach is to read rainfall not as an atmospheric figure alone but together with the signals that represent its movement below the surface; to make local hydrogeological dynamics visible instead of applying global thresholds; and to provide a decision-support layer grounded in physical reality and catchment-scale processes rather than theoretical suitability maps.
Question, analysis, output
| Question | Analysis | Output |
|---|---|---|
| Is this parcel or catchment exposed to flooding, and to what degree? | Catchment-scale flood model | Flood depth and extent maps |
| Is the rainfall increase in this region converting into groundwater reserve? | Process-based groundwater assessment | Hydrogeological evaluation for site and regional prioritisation |
| What is the financial exposure behind this risk? | Risk quantification with UrClimate Score / Next | Input for physical climate risk reporting |
Detailed hydraulic modelling: HEC-RAS
When a study needs to go beyond catchment-scale prioritisation and deliver flood depth, flow velocity and water surface elevation for a specific site, the work deepens into HEC-RAS based hydraulic modelling. In that scope the site is scanned with LiDAR to build a sub-metre terrain model, design discharges are derived from observed streamflow records, and flood extent maps are produced for scenarios such as Q100 and Q500. See HEC-RAS Flood and Hydraulic Modelling for details.
Process and deliverables
| Steps | Outputs |
|---|---|
| Compiling catchment boundaries together with topography, geology and land-cover data → catchment-scale modelling of the rainfall, infiltration, runoff and evapotranspiration processes → generating flood and groundwater scenarios → carrying the results into risk quantification or climate risk reporting | Flood depth and extent maps, site prioritisation assessment, physical risk input for reporting |
Method and evidence
No named client project is currently published for this service. The data argument behind the approach is set out in our articles on rising flood risks and data-driven analysis, while the risk quantification side can be explored on the UrClimate Score and UrClimate Next product pages.
Frequently asked questions
- What is flash-flood risk and why does it matter?
- A flash flood occurs when intense rainfall over a short period produces surface runoff faster than the ground can absorb it. Where it is not assessed in advance at parcel or catchment scale, it is a serious physical risk to basements, infrastructure and critical equipment.
- Why is an increase in rainfall not a sufficient indicator on its own?
- Rainfall is only an input to the hydrological system. How much of that input becomes groundwater, and how much leaves as surface runoff and evapotranspiration, is determined by the topography, geology and land cover of the region. Two catchments receiving the same rainfall can show entirely different flood and groundwater behaviour.
- How does this analysis feed into climate risk reporting?
- Flood risk is one of the physical risk categories assessed by reporting frameworks such as TSRS. For scope and format, see our TSRS Climate Risk Reporting page.
- Which data sources are used?
- Publicly available climate and weather observations, including national meteorological records and Copernicus datasets, are assessed together with the topography, geology and land-cover data of the region.
- Is this service only offered through the UrClimate products?
- No. Flood and groundwater risk analysis is delivered as a standalone engineering service on a project basis, and can additionally be connected to risk quantification through UrClimate Score and Next.
Related content
- HEC-RAS Flood and Hydraulic Modelling: LiDAR site survey, 1D/2D hydraulic modelling, scenarios and output maps.
- Meteorology & Climate Data: The observation and climate data layer the models rest on.
- TSRS Climate Risk Reporting: Our physical climate risk reporting service.
- All Solutions: The full directory of our services.