Imperviousness is directly related to urban development. It can be defined as the sum of roads, car parks, sidewalks, rooftops and
other impermeable surfaces of the urban landscape. Impervious surfaces no longer allow rainfall to soak into the ground.
Consequently, most rainfall is directly converted into stormwater runoff. Aside from causing water pollution and other environmental
problems, this can be too much for the existing drainage system to handle and lead to floods. Up to now, the usual response to floods
in Brussels lay in the improvement of the drainage system and the digging of stormwater reservoirs, but increasing awareness has
led the Ministry of the Brussels-capital Region (MBCR) to consider changing its policy as regards imperviousness. The first step in
this process consists in evaluating the evolution of the situation, as a basis for further analysis. The objective of this study
is to measure imperviousness evolution from the 1950s up to now in the Brussels-capital region, with extensions following the
limits of the watersheds (i.e. about 200 sqkm in total). In this framework, the percentage of imperviousness is estimated in 1-ha grid
squares.The use of high- and very high-resolution satellite remotely sensed data is the fastest and most efficient way to estimate
the extent of imperviousness. However, because high-resolution data have been available since the 1980s only, and very
high-resolution data since 1999 only, the study period is divided into 1955-1985 and 1987-2005. Different data types are used within these
two periods, according to their availability and relevance.The results of the study will be : first, imperviousness maps at each
date considered; second, maps displaying the evolution index of the impervious surfaces percentage; and third, statistics and/or
maps aggregating the percentages and/or their evolution on the level of the different spatial entities of interest.