Mapping of rainwater harvesting potential derived from building data-based hydrological models through the case study of Szeged, Hungary

Urban water cycle suffers from ever increasing problems for what a modern city needs to prepare. The water cycle of most cities is not implemented in a sustainable way, which needs to be redesigned as a result of climate change. Through the climate change more extreme weather situations are expected to affect the life of cities. From aspect of the water cycle, this means extremely unequally distributed rainwater supply throughout the year. During drought periods, urban vegetation requires irrigation, often covered by cities with drinking water, a practice widely considered to be unsustainable. Therefore, finding appropriate methods and resources is crucial, in order to reduce the exposure of cities to the increasing climate extremes.

By collecting large amounts of rainwater and using it as irrigation water during droughts, it is possible to avoid the unnecessary waste of drinking water and to help preserve its limited supply in the future. A significant amount of precipitation flows through the surface of urban micro-catchments (e.g. roofs or other building surfaces), a significant part of which leaves the city through the sewer system without any usage.

The aim of our research is to create a rainwater harvesting potential map based on a building database in the study area of Szeged, Hungary. We used this building database to estimate the amount of rainwater that flows or evaporates on the top of buildings during a year, as well as the amount that can be considered as potentially collectable water. In addition to the GIS data, a complex meteorological database was also used.

The study was carried out in the EPA SWMM model. The building database contains nearly 20,000 building polygons, of which nearly every single polygon represents a separate catchment for this research. Based on the database, it is also possible to separate slope/pitched roof and flat roofs, which also allowed us to determine which roofs have the potential to be used as a green roofs to further facilitate efficient rainwater harvesting. Our result can be used to produce both city- and district-level (downtown, housing estate, garden house zones) summaries about the rainwater harvesting possibilities within Szeged. These results can be used to delineate areas where harvesting systems can be realistically installed. In addition to the spatial data, we can also acquire information on the seasonal distribution of the precipitation and thus the amount of collected water which can be used in drought periods.

Through our results we can get estimate the volume of rainwater that can be potentially collected from the surfaces of the building in Szeged. We believe, that our research may encourage urban planners to make into greater account the potential of rainwater storage in the local planning processes. This can greatly contribute to the decision-making processes at the local levels, and to the expansion of the knowledge related to green space-based integrated urban infrastructure management.