Soil sealing

Soil sealing is the covering of ground with material water cannot pass through: asphalt, concrete, buildings. In German, Bodenversiegelung, and the share of an area affected is the Versiegelungsgrad. It is usually reported as a percentage of a district or a parcel.

It matters for two climate risks at once. Sealed ground cannot absorb rainfall, so water runs off instead of infiltrating, which is what turns heavy rain into local flooding. And sealed surfaces store and release heat, which is a large part of why dense districts stay warmer at night than their surroundings.

For analysis the useful distinction is between fully sealed and permeable surfaces. Gravel, grass pavers and permeable paving all sit in between, so a binary sealed or unsealed map overstates the problem in some places and understates it elsewhere. Whichever categories you use, name them, because the headline percentage depends entirely on where the line was drawn.