What if the next rain bomb falls over Flanders?

Between 13 and 15 July 2021, exceptional amounts of rain fell over the south and east of Belgium. 39 people lost their lives, more than 38,000 homes were affected, and damage to homes and infrastructure amounts to 4 billion euros.
 All of a sudden, climate change calls very close to home.

What if the next rain bomb falls over Flanders?

The wettest summer in two centuries gave an unexpected twist to CurieuzeNeuzen in de Tuin, the community science project uniting 5000 citizens across Flanders to measure the impact of extreme events on their own properties. We got a unique view of how our gardens and nature reserves help buffer extreme precipitation. What we found? Gardens are powerful sponges, but in our cities and valley areas, they are under pressure. Newspaper partner De Standaard created a beautiful long-read about the story, impressively visualizing the role of gardens – and how we interact with those gardens – in the battle against increasingly extreme events.

You can find the full story here (in Dutch). This is a short summary – and translation to English, from the text written by amazing journalist Ine Renson.

Explore the buffering capacity of our gardens on this interactive map!

Our network shows beautifully that our gardens can act as very efficient sponges. If we compare the soil moisture measurements from our sensors across the whole summer season with the precipitation data from the Royal Meteorological Institute (RMI), it appears the Flemish gardens have collected on average at least 60% of the rainwater that has fallen.

The ‘rain bomb’ of July 15th, affecting largely Germany and Wallonia, east and south of Flanders. However, rain in the east of Flanders added up to over 45 L/m² or even 80 L/m² in one day (dark blue dots on the map)

On that 15th of July, the famous rain bomb, weather patterns were unique, providing us with an unprecedented opportunity to disentangle what defines our garden sponges during extreme rainfall events.

Gardens as sponges: purple gardens absorbed 90% or more of the precipitation, a yellow dot indicates numbers from 0 to 5%

Interestingly, gardens across the regions sponged very differently: in two of the main cities in the region – Antwerpen and Mechelen – gardens sponged A LOT of the water. in southern Limburg, the sponges were virtually inactive.

So what drives these patterns? In De Standaard, we go deeper into all the underlying variables. There is a ton of things we have nothing to say about: more rain gives relatively lower sponge percentages. Already saturated gardens obviously cannot sponge more. But also: gardens in urban areas and valleys had to sponge a lot harder, indicating that there is a lot of pressure there during extreme rain events, with water flowing in from elsewhere.

Managing your garden as a sponge

So, what can we do with this information? Our partnership with De Standaard allows us to communicate those results directly to those who need to hear it most: the general public. We found that garden management could have a significant effect on the sponge function. For example, we found that planting trees could help. It reduces the amount of water directly hitting the ground, and thus reduces risks for flooding during extreme rain events.

Yet the main solution: turn the grey into green! The higher the percentage of impervious area in your garden (buildings, driveway, terraces…), the higher the pressure on the remaining green. But also: the more urbanized your neighbourhood, the harder your garden will have to work.

Or as they put it so beautifully in De Standaard:

A permeable driveway, a smaller terrace: it really makes a difference. In the event of a flood, it can determine whether or not a neighborhood will be flooded.
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