Our climate is slowly changing, what climate change means differs per region, but in general it can be said that weather patterns are becoming more and more extreme. The chances of extreme rainfall will increase and this requires a re-evaluation of local land-usages . In the Dutch context, these evaluations of land-usages are part of the Delta-Programme in the form of a compulsory climate-scan. Every municipality in the Netherlands is required to perform such a scan, so that every municipality can make its own plans to deal with the effects of climate change. One of the most important ways in order to increase climate-resilience, especially in the urban environment, is by increasing the amount of Urban Green spaces. Urban green spaces are all the vegetated areas in the urban environment. The term urban green space embodies all parks, recreational spaces, gardens, lawns, brownfields, wasteland areas and woodlands in the urban environment (Francis & Chadwick, 2013).


Picture 1: The Green/Blue Network of Groningen.

In his research, Allard Hans Roest, focused on the smallest form of urban green space, the garden, and the effects gardens have on the urban flood-resilience. The interest in this subject came to him in his previous home in Groningen, when he saw that all the water from the soil-sealed gardens in his vicinity flowed towards one sewage entry and wanted to know more about the effects gardens have on the sewage system and climate-scans in general. When he started to search for this subject on the internet, he found out that in the scientific sense gardens are still a relatively underrepresented subject of research . This while around 40% of all urban land is owned by private owners. In his research, he used the Semi-Automatic Classification Plugin QGIS in order to determine the land-use in gardens. Two main datasets were used in this classification, most importantly a high-resolution Aerial Photograph provided by the Municipality of Groningen and a satellite image of the city. Both of these datasets were analyzed, and only the image by the municipality of Groningen proved to be useful in determining land-use in gardens. The outcomes of these analyses were than used to gain a better under-standing in soil-sealing dynamics and effects for the city of Groningen, as well as in three case-study areas.

In his research, Allard found that most gardens in Groningen are mostly soil-sealed and have limited room for vegetation and water absorption (figure 1). This is due to a number of factors, including garden size and building density in neighbourhoods (figures 2 and 3). In the survey, it was found that most people do not take environmental impacts into account when designing a garden, mostly focusing on esthetics or ease.


Picture 2: Garden house per neighbourhood in Groningen.


Picture 3: Building density per neighbourhood in Groningen.

This extent of soil-sealing is problematic in a city like Groningen, where a large share of the sewage system is shared (figure 4). Meaning that both wastewater and rainwater are drained using the same infrastructure. In his research, it is concluded that in three different scenario’s, the capacity of the sewage system shifts from an extreme shower of 19.6 millimeters in an hour to more common rainfall, increasing the risks of flooding in both public as private space.


Picture 4: Water draining infrastructure in Groningen.

The conclusion of his research is that climate-adaptation and climate change are complex in nature and require an approach where both the general public as governmental organizations work together in order to increase resilience. But that this cooperation is not yet seen in planning practice, where governments often focus on large-scale projects to increase the drainage capacity and relies mostly on participatory approaches in order to stimulate greener gardens and the general public often looking towards the government to provide them climate-resilience rather than actively participating in climate-adaptation.

This article was published in the Northern Netherlands edition, May 2018.

Credit Pictures:

Picture 1 (and Top photo): Slagboom & Peeters (2016), Kadaster (2018), Gemeente Groningen (2017).
Picture 2: Slagboom & Peeters (2016), Kadaster (2018), Gemeente Groningen (2017) and edited by Geodienst.
Picture 3: Kadaster (2018), Gemeente Groningen (2017).
Picture 4: JenL Datamanagement (2017), Kadaster (2018), Gemeente Groningen (2017).

Sources:

  • Lenderink, G. and E. van Meijgaard (2008) Increase in hourly precipitation extremes beyond expectations from temperature changes. Nature Geoscience, vol1 (8), pp.511-514.
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  • Freeman, C., Dickenson, K.J.M, Porter, S. and Heezik, van Y. (2012) “My Garden is an expression of me”: Exploring householders’ relation-ships with their garden. Journal of Environmental Psychology, vol 32., pp135-143.
  • Zwaagstra, C. (2014)The contribution of soil sealing in urban private gardens to runoff and urban heating. [Online] Available at: http:// edepot.wur.nl/323177. [Last Accessed 28-05-2018]