Climate Change Stress Testing Across a Central London Portfolio

In 2020 FPS were instructed to undertake a climate change stress test across a mixed central London portfolio comprising restaurants, members’ clubs, boutique retail, commercial space and residential buildings. In asset terms the estate was worth several hundred million pounds.

The client already had access to national datasets and high-level risk information. What they did not have was an understanding of how those risks translated at building level, or how the buildings would behave during an intense rainfall event. This was not a desktop exercise. It required detailed walkovers, drainage reviews, and direct engagement with the teams responsible for operating the buildings day to day.

The dominant risk was the lack of asset knowledge

Many of the buildings appeared outwardly robust. However, once we started to interrogate them at a practical level a consistent issue emerged. The greatest vulnerability was not necessarily the predicted flood depth. It was the absence of reliable information about the assets themselves.

In a number of cases there was no confirmed understanding of how the drainage connected, access routes, or how pumped systems were maintained. Historic alterations had created voids and redundant structures that were no longer recorded, but still influenced the way water would move through the building.

That uncertainty changes the risk profile. Internal flooding in dense urban environments is often triggered by a very small issue in the wrong location. A blocked gulley, a failed non-return valve or a pump that does not activate when it should, can cause significant damage regardless of what the national surface water map suggests.

Stress testing the real behaviour of each building

The project started with a desktop review of national surface water data, treated as a strategic overview. Each property was then assessed in its local context, taking into account street levels, topography, cambers, basement thresholds, pavement lights and the condition and connectivity of the drainage system – where accessible.

Walking the sites was critical. It allows you to see the actual routes of ingress and the points where water will accumulate. It also allows you to test the dataset against reality, which in central London is rarely straightforward.

The discussions with site managers, engineers and building staff were equally important. They know which drains struggle in heavy rainfall, when pumps start to run continuously and where water appears first. That operational knowledge repeatedly confirmed the physical mechanisms we were identifying.

It was also valuable to walk the surrounding streets and observe how similar buildings were performing in comparable rainfall conditions. Recurring issues such as blocked gulleys, low external thresholds and localised ponding were recorded and fed back into the portfolio risk register.

This showed how two similar buildings on the same street with the same mapped flood risk, could perform completely differently where one had known, mapped and understood drainage connectivity, and a maintenance plan, and the other did not.

What the assessment showed

A clear pattern developed across the portfolio. Surface water mapping on its own was not always a reliable indicator of building-level risk.

In many cases the more significant issue was the potential for surcharge within ageing combined sewer connections and the reliance on systems with limited monitoring, knowledge or resilience.

Validation during a major rainfall event

Approximately a year after the study was completed a major storm affected London slightly to the northwest of the portfolio.

The flooding that occurred were the exact types of mechanisms we had identified. They were localised surface water floods, with drainage backflow, and basement flats significantly impacted. For the client this provided real confidence that the methodology had correctly identified the practical risks and that the prioritised actions were the right ones. It highlighted why vulnerable or lower ground areas should have a Flood Warning and Evacuation Plan- although noting the surface water floods had limited warning, which must be factored into response planning.

From climate risk to asset management strategy

The value of the work was that it translated climate change from an abstract future issue into a building-specific management plan.

Immediate actions focused on confirming how the existing systems functioned and strengthening known points of weakness. Longer term, the estate moved towards a structured approach to drainage knowledge, planned maintenance and the integration of flood resilience into refurbishment programmes.

This gave the property directors, risk managers and insurers a common evidence base and allowed investment decisions to be made in a planned and proportionate way.

The work also identified the strategic benefit of adopting a central BIM-led information platform. A verified record of assets, certification and drainage infrastructure would allow faster and more informed decision making during a flood event, reduce business interruption and provide a consistent technical baseline for maintenance and refurbishment across the portfolio. As part of this approach, drainage connectivity and condition can be confirmed progressively and uploaded to the central system.

Project Outcome

The client moved from a position where risk was described in general terms to one where the behaviour of each building was understood. It provided a prioritised pathway for capital expenditure, improved operational resilience and a framework for managing drainage and infrastructure information across the estate.