Effects of 66 years of water management and hydroclimatic change on the urban hydrology and water quality of the Panke catchment, Berlin, Germany

Long-term records of combined stream flow and water chemistry can be an invaluable source of information on changes in the quantity and quality of water resources. To understand the effect of hydroclimate and water management on the heavily urbanized Panke catchment in Berlin, Germany, an extensive search, collation and digitization of historic data from various sources was undertaken. This integrated a unique 66-year spatially distributed record of stream water quality, a 21-year record of groundwater quality and a 31-year stream flow record. These data were analysed in the context of hydroclimatic variability, as well as the history and technological evolution of water resource management in the catchment. To contextualize the effect of droughts, "average" and wet years the Standard Precipitation Index (SPI) was applied. As upstream sites have been less regulated by human impacts, the flow regime is most sensitive to changes in hydroclimatic conditions, while downstream sites are more influenced by wastewater effluents, urban storm drains and inter-basin transfers for flood alleviation. However, at all sites, a general increase in maximum event discharge was observed until a recent drought, starting in 2018. In general, water quality in the catchment has gradually improved as a result of management change and increasingly effective wastewater treatment, though in some places legacy and/or contemporary urban and rural groundwater contamination may be affecting the stream. Hydroclimatic changes, particularly drought years can affect water quality classes, and alter the chemostatic/dynamic behaviour of catchment export patterns. These insights from the Panke catchment underline the importance of strategic adaptation and improvement of water treatment and water resource management in order to enhance the quality of urban water courses. It also demonstrates the importance of long-term integrated data sets.