Urban green spaces have different functions, reaching from recreational use over the conservation of urban biodiversity to hazard mitigation. The quantity, quality, pattern and distribution of urban green spaces give indication for life quality in a neighbourhood of a city. Their monitoring and assessment can therewith be used as indicator for social characterization of different areas in a city and for life quality studies. Also, it indicates the ecological value of neighbourhoods in an urban agglomeration, an increasingly important factor in sustainable urban development. Besides that, green spaces are an important element in the water cycle as vegetation cover leads to transpiration but also absorbs rainfall and eventually produces runoff after no more water can infiltrate. It does therewith have different hydrological properties than the built-up environment in a city that cause less infiltration and higher runoff. With remote sensing methods and data the nature space potential of the urban agglomeration will be investigated. So the quantity of urban green, its spatial distribution, networking and changes in its configuration will be analysed and assessed with satellite imageries and GIS data sets. Indicators such as the above mentioned spatial distribution, networking and configuration, and beyond these, the green structure (its linear or spatial form, isolation or fragmentation), dynamics (monitoring of changing processes) and patterns (neighbourhood relationships to other land uses such as residential or commercial districts) help to develop scenarios that can be used to estimate the reaction of an urban environment to extreme rainfall and to suggest improved land use planning in order to mitigate the flood hazard. The study area for this approach is Santiago de Chile, a large city with an urban setting very representative for Latin America. The presented methodology is used to assess and monitor the characteristics of urban green spaces in an expanding urban environment. Embedded in the project ‘Risk Habitat Megacity’ the results of the study are analysed and interpreted in a technical as well as a socioscientific context and thus provide analytical starting points for various disciplines.