Sealing ground is a problem which negatively impacts the water balance since the soil cannot be used as a water puffer anymore. This results in surface water not being able to be added to the groundwater level which can directly lead to flooding. On the other hand, this water does not get added to the groundwater which can have severe consequences for the quality of the groundwater and the actual amount. Lacking groundwater will lead to more concentrated toxic substances and in the far run to possible draughts.
This becomes especially a problem when formally not sealed land is affected, for example in periurban or rural areas, where agriculture and horticulture have the largest impact on sealing ground. This goes for greenhouses and traditional agriculture likewise with the latter having a different but not neglectable influence.
It is required by German Nature Conservation Act to implement compensation areas for every construction project which seals additional ground. A construction ground is assessed beforehand and valence points respective to the covered area are awarded. For example, a natural forest or a meadow has higher valence per square meter then a lawn or a driveway. The amount of points is awarded based on detailed lists. If a construction projects yields a decreased valence after assessment, compensation areas must be identified, either on site or nearby which can be accompanied by additional cost. Depending on the project this could even be a driving factor for it to rendered uneconomic.
If we look at greenhouses which get installed on rooftops, we now see two advantages in comparison to on ground installation. The first advantage is quite obvious: We do not seal any additional land while simultaneously increasing the effective agricultural area.
The second advantage comes with the rainwater collection and direct usage in the greenhouse. Here, the water can be used directly in the growing systems of the greenhouse instead of being fed to the sewer system reducing the impact in rainwater heavy seasons.
Having a rooftop greenhouse can therefore have additional positive impacts on the environment beyond the reduction of CO2 emissions
David VOLK, EBF GmbH - Energy Biosphere Food