Land use in urbanised catchments has a decisive impact on the well-being of aquatic ecosystems. In densely populated urban areas human activity has a pronounced effect on the hydrological cycle. Whereas in pristine regions most runoff water from rain and snowmelt is absorbed by soil, highly efficient sewer systems in urbanised catchments will carry runoff water to the nearest waterways.
High-efficiency drying has reduced the ability of soil to filter and clean nutrients and other contaminants from runoff water, which exposes adjacent waterways both to eutrophication and to other water quality problems. The impacts of diffuse pollution on the state of waterways have been extensively researched from an agriculture point of view, but less is known about the corresponding effects of urban development.
The URCA project is intended to explore the impacts of urbanisation on the characteristics of runoff water. This will be done by building automatic runoff stations at ten catchment sites along an urban-rural gradient in Helsinki and Lahti, which will allow a detailed analysis of the quality of water in runoff sewers, including measurements of nutrient and heavy metal concentrations. Precipitation levels at these sites will be determined using dual-radar polarisation observations.
Terrain features will be mapped using LiDar elevation data as well as aerial photography and urban planning maps to identify impervious areas. These areas, such as building roofs and parking lots, have a decisive impact on the formation of runoff water from urban areas. The data obtained from these measurements will be used to develop a mathematical model to describe the hydrology in these areas. Using this model, the results can be generalised beyond the research areas and to new changing climate conditions.
Another area of interest in the research is the role of urban green belts as ecosystem service providers that can help improve the quality of runoff water.