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The model region Berlin - Brandenburg

The model region Berlin-Brandenburg is populated by approximately six million people. With an annual mean precipitation of 580 mm (1981-2010), it belongs to one of the driest parts of Germany. Nevertheless, past events have shown the risk of flooding in the same area. Within the model region, CliWaC will focus on three case studies that represent significantly different systems and challenges embedded in diverse social-ecological contexts: a lake system and its surrounding area; the Spree catchment; and urban infrastructure.

Each of these case studies is characterised by deficits in the scientific understanding and by insufficient data and information, by challenges of high ecological, economic and social relevance, by a multitude of potential actions and responsible actors at different political and administrative levels, and by target conflicts and barrier effects that demand coordinated action. The case studies, although addressing specific challenges, are related to each other, both in terms of climate influences, in terms of water flows in the area considered and in terms of their management and stakeholder involvement. The first case study addresses the problem of changing groundwater resources and related issues of two lakes and their drainage basins belonging to a common hydrogeological system that reaches across the state border of Berlin-Brandenburg. The second case study deals with the river Spree as a hydrological system linking Berlin and Brandenburg, as well as different local councils in Brandenburg. While the first two case studies mainly focus on problems induced by decreasing water availability, the third case study investigates heavy rainfall events in and nearby Berlin. All WPs of the three Parts A, B and C will contribute to the case studies to close scientific gaps and to develop strategies for implementation of effective actions.

Case Study 1 - The hydrogeological system of the Groß Glienicker See and Sacrower See

The two lakes Groß Glienicker See and Sacrower Lake are part of a coupled hydrogeological system of glacial lakes formed after deglaciation of the Weichselian Baltic Ice Sheet. Both lakes are almost entirely fed by groundwater that is recharged by net precipitation in the not well-constrained hydrogeological drainage basins that cross the state border between Berlin and Brandenburg. Today, both lakes do no longer have surface outlets. The connection between both lakes dried out in 1996, while the connection between the Sacrower See and the Havel was artificially closed in 1986 to prevent eutrophic water from the Havel entering the Sacrower See.

Case Study 2 - Spree river and Spree catchment

With a total length of 382 km, the river Spree connects the Upper Lusatia low mountainous region in Saxony with the Elbe-Havel-system. The complex water network of the Spree region is a sensitive and vulnerable ecosystem with great importance for drinking water production, irrigation in agriculture, but also for recreation, nature conservation and landscape protection. With the decline of lignite mining and the construction of dams, discharges have decreased, resulting in a hydrologically dampened flow regime compared to other low mountain catchments. The dry summers of recent years have posed problems for agricultural production in locations far from groundwater. The increasing occurrence of unusually long dry periods combined with heat waves has already had negative impacts on agricultural yields, wetlands and ecosystem functioning, and has increased pressure on the water balance. Crop failures in recent years and forests suffering from prolonged droughts show that we urgently need to further quantify the potential impacts of projected climate change on agricultural production and forests.  In this study, we aim to understand how droughts affect the productivity and resilience of managed ecosystems, forests, grasslands, croplands and urban areas, and the feedbacks between drought-induced ecosystem changes and water flows. Through an integrative and sectoral assessment, we ultimately have the opportunity to quantify trade-offs and synergies, as well as the costs and benefits of specific actions.

Case Study 3 - Extreme rainfall in an urban area

Flooding arising from heavy rainfall events has led to damage to households in parts of Berlin and its surroundings. Disruptions in road traffic as well as and water ingress via stairway accesses into underground train stations affected the city’s mobility system. The wastewater system of the city was affected by peaks of polluted water, especially in conjunction with a preceding dry period which has increased the level of pollutants. In such situations, sewer overflow occurs and wastewater is directly routed into rivers, which currently happens about two dozen times per year in Berlin. The risks for these events under present day and future conditions, and the exploration of possible measures to alleviate the problems, are addressed in the project.