New Web Tool Identifies Urban Pollution Hotspots, Aiding Climate Adaptation Strategies

Berlin, Germany – As climate change intensifies, leading to more frequent and severe rainfall events, European cities are grappling with a growing challenge: the contamination of waterways by urban runoff. Roads, plazas, green spaces, and rooftops, often impermeable, act as conduits, washing pollutants like tire wear particles, oil residues, and heavy metals into sewage systems and, ultimately, into rivers and lakes. However, some surfaces yield comparatively cleaner rainwater, presenting an opportunity for reuse. To address this critical issue, scientists at the Technical University of Berlin have developed an innovative interactive web tool called CleanCityCover, designed to help municipalities pinpoint pollution hotspots and plan more targeted urban water management strategies.

The CleanCityCover tool is a product of the EU Horizon project WATERUN, which brings together 14 European partners to pioneer new methodologies for water-sensitive urban development. This initiative aims to tackle the pervasive problem of diffuse pollution, a major threat to urban surface waters across Europe that significantly degrades the ecological health of rivers, lakes, and groundwater bodies.

The Pervasive Problem of Diffuse Urban Pollution

Diffuse pollution refers to contaminants that enter water bodies from widespread, non-point sources, making them notoriously difficult to control. During heavy rainfall, these pollutants are leached from sealed surfaces – such as roads, parking lots, and rooftops – and are transported through rainwater drainage systems. Depending on the system’s design, this runoff may be discharged directly into waterways or mixed with household wastewater before reaching its destination.

The spectrum of pollutants carried by urban runoff is broad and concerning. It includes microplastics generated from tire abrasion, heavy metals from metal roofs, oil residues from traffic, and organic substances from various sources. In the context of climate adaptation, understanding which surfaces release specific pollutants and where interventions like containment, purification, or rainwater reuse are most effective is becoming increasingly vital. This is especially true as climate change makes extreme rainfall events a more common occurrence.

CleanCityCover: A Digital Compass for Urban Water Management

Developed at the TU Berlin by doctoral candidate Boney Joseph and Professor Eva Paton, with contributions from visiting scholar Dr. Nasrin Haacke, CleanCityCover is a web-based tool engineered to assess the pollution potential of urban surface runoff. Programmed and parameterized for several European cities, it allows users to identify critical source areas of diffuse urban pollution. Simultaneously, the tool highlights surfaces that generate relatively clean runoff, making them suitable for potential rainwater harvesting and reuse.

"Our goal was to create a practical tool that could be transferred to other EU cities," explained Professor Eva Paton, Head of the Ecohydrology Department at TU Berlin. "CleanCityCover helps cities better understand where diffuse pollution originates and where interventions can have the greatest impact. The tool is intended to support municipalities, environmental authorities, water suppliers, and urban drainage companies in planning targeted measures for pollutant containment and identifying suitable locations for blue-green infrastructure."

The tool incorporates an integrated ranking system for pollutant sources, which aids in the planning of blue-green infrastructure – a network of natural and semi-natural elements designed to manage water and enhance urban biodiversity. This planning assistance extends from individual sites to entire city districts, offering a scalable approach to tackling urban water challenges.

Piloted in European Cities: Aarhus, Santiago de Compostela, and Berlin

As part of the WATERUN project, CleanCityCover has been parameterized and applied in three distinct European urban environments: Aarhus, Denmark; Santiago de Compostela, Spain; and Berlin, Germany. Currently, the tool accounts for three primary types of pollution: atmospheric deposition, traffic-related contamination (varying with traffic intensity), and heavy metals from metal roofs.

The application of CleanCityCover in these cities has been instrumental in identifying urban pollution hotspots. The findings from these pilot studies are now poised to provide practical support for the planning and implementation of blue-green infrastructure projects. These projects often involve the integration of green spaces, permeable surfaces, and water management features into the urban fabric to mitigate the impacts of heavy rainfall and improve water quality.

Unveiling Surprising Similarities and Critical Compound Events

Prior to the full development of CleanCityCover, preliminary studies analyzed urban surface runoff in ten cities across Central Europe, stretching from Southern France to Denmark. These studies revealed a surprisingly consistent pattern in runoff behavior across smaller, medium, and large flow events, as well as in the seasonality of their occurrence.

However, a nuanced observation emerged: cities located in the central part of the studied geographical area, such as Berlin and Essen, experienced more frequent short, but intense, runoff events. Further research, including a recently published BigData analysis for the Berlin metropolitan area, shed light on a critical factor influencing water quality: the impact of preceding dry periods.

The analysis demonstrated that it is not always the most extreme rainfall events that have the greatest impact on the water quality of Berlin’s rivers. Instead, less severe heavy rainfall events can have a significant negative effect if they follow extended dry spells. These phenomena, known as "compound events," are now explicitly considered in the setup of the CleanCityCover tool, recognizing their amplified contribution to diffuse urban pollution. This insight underscores the importance of understanding the full hydrological context, not just the magnitude of individual rainfall events.

Addressing the Pervasive Issue of Oil Contamination in Urban Areas

Beyond the broader categories of pollution, a dedicated accompanying study by student Luz von der Groeben focused on diffuse oil contamination in urban environments, using Berlin as a case study. This research involved evaluating alarm data from the Berlin Fire Brigade regarding oil pollution incidents on public streets.

Additionally, researchers meticulously documented the number and size of oil patches on roadways and parking areas along selected street sections in Berlin-Kreuzberg. The findings revealed a disturbingly high prevalence of such contaminants. Oil pollution not only damages road surfaces but also acts as a diffuse pollutant, posing particularly detrimental consequences for aquatic life. The researchers concluded that there is a pressing need for more effective methods to detect oil contamination and reduce its discharge into waterways.

Enabling Sustainable Urban Water Management for Climate Resilience

For cities aiming to adapt to climate change and implement sustainable rainwater management practices, precise spatial information is indispensable. In Berlin, this need is further amplified by the city’s Climate Adaptation Law (KAnGBln). This legislation mandates measures to protect against heat, drought, and heavy rainfall, promoting strategies such as urban cooling, tree planting, increased green spaces, and the infiltration and reuse of rainwater.

CleanCityCover directly supports these efforts by visually highlighting heavily polluted areas alongside surfaces with comparatively cleaner runoff. This functionality allows for a more informed assessment of suitable locations for blue-green infrastructure and rainwater harvesting systems. Given that the methodology is transferable to diverse urban settings, the tool has the potential to assist municipalities across Europe in improving water quality, implementing nature-based solutions, and strengthening their overall climate resilience.

The development and deployment of tools like CleanCityCover represent a crucial step forward in urban planning and environmental stewardship. By providing data-driven insights into the complex dynamics of urban water pollution, these innovations empower cities to make more informed decisions, protect vital water resources, and build more sustainable and resilient urban environments for the future. The collaborative spirit of projects like WATERUN, bringing together diverse expertise and international partners, is essential in forging these innovative solutions to shared global challenges.

Source: Technical University of Berlin (2026) | Author: Barbara Halstenberg. Originally published in German.