Wastewater discharges and urban land cover dominate urban hydrology signals across England and Wales

Urbanisation is a critical driver of changes in streamflow. These changes are not uniform across catchments due to the diverse changes to water sources, storage, and pathways in urban river systems from impervious areas, abstractions, sewage networks, and sewage treatment plans. While land cover data are typically used to explain urbanisation, water management practices are poorly quantified. Consequently, urbanisation impacts are often difficult to detect and quantify, and the relative impact of these factors is currently poorly understood.

Here, we assess urban impacts on streamflow dynamics for a large-sample of catchments across England and Wales using data characterising water management practices and land cover. We quantify urban impacts on a wide range of streamflow dynamics (flow magnitudes, variability, frequency and duration) using random forest models. We demonstrate that wastewater discharges from sewage treatment plants and urban land cover dominate urban hydrology signals across England and Wales and have different impacts on streamflow dynamics. Wastewater discharges increase low flows and reduce flashiness in urban catchments, while urban land cover increases flashiness and frequency of medium and high flow events. We demonstrate the need to move beyond land cover metrics and include other features of urban river systems in large-sample hydrological analyses to quantify current and future drivers of urban streamflow.