Wasserwirtschaft und Hydrosystemmodellierung

CliWaC - Climate and Water under Change

Description

As a transdisciplinary research initiative of the Berlin University Alliance, the Einstein Research Unit Climate and Water under Change (CliWaC) is dedicated to the investigation of water-related risks of climate change in the Berlin-Brandenburg region. In doing so, CliWaC will bring together social and natural science as well as practical expertise from stakeholders to develop mitigation and adaptation measures against climate change impacts. 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. 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 (www.cliwac.de).

We are involved in two of the three case studies:

- Case study 1: The hydrogeological system of Groß Glienicker and Sacrower Lake

and

- Case study 2: Heavy rainfall in Berlin

Link to CliWaC webpage: https://www.cliwac.de/

Study Area

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.

Case study 3: Heavy rainfall in Berlin

Hydrodynamic rainfall-runoff simulations of heavy rainfall events have been carried out with the in-house robust 2D shallow water modell hms++. Digital elevation model, buildings and land use are taken into account to set-up the model. Results include flooding areas, spatial distributions and temporal developments of water depths, flow velocities and discharges. By now, two types of investigations have been finished:

  1. Simulations for entire Berlin for a statistical rainfall event: KOSTRA-DWD-2020, 60 min, 100-year, Euler-2 design rainfall (cell length: 6 m)
  2. Ensemble-simulations for a part of Berlin (360 km², cell length: 10 m)

The ensemble simulations include 9 heavy rainfall event with different spatio-temporal distribution, which have been resimulated by Katrin Nissen & Uwe Ullbrich (FU Berlin). Each realization is equally probable and could have occurred in reality under the given initial conditions. In the work shown here, the large-scale atmospheric initial situation of 01.06.2018 was used, which led to a heavy rain event in Berlin. The results include the spatial distributions and temporal developments for selected hotspots for the 9 ensemble simulations, the event on 1 June 2018 observed by radar-data (Radolan), and the aforementioned statistical heavy rainfall event (KOSTRA).

Current investigations deal with the effect of infiltration, drainage systems and blue-green infrastucture.

Most of the results have been generated within two Bachelor theses:

Pia Gronau (2023): Hydrodynamische Niederschlags-Abfluss-Simulationen für Gesamt-Berlin und Untersuchungen zur geeigneten Gitterauflösung

Elsa M. Kronke (2023): Hydrodynamische N-A-Ensemblesimulation mit verschiedenen räumlich-zeitlichen Verteilungen von Starkniederschlägen zur Untersuchung von Überflutungsflächen in einem Teilgebiet von Berlin

Case study 1: Hydrogeological system of Groß Glienicker & Sacrower See

1. Estimation of the groundwater balance in Groß-Glienicker See

Using climate data from surrounding weather stations of DWD and different methods to calculate evaporation from open water bodies, the net groundwater flow is estimated as residual in the water balance equation:

𝑑𝑆/𝑑𝑡 = 𝑄𝑠,𝑖𝑛 + 𝑃 + 𝑄𝑔𝑤,𝑖𝑛 − 𝑄𝑠,𝑜𝑢𝑡 − 𝐸 − 𝑄𝑔𝑤,𝑜𝑢𝑡

dS/dt : Storage change: based on lake water level and geometry

P: Precipitation: interpolated from 7 DWD stations

E: Evaporation: climate data interpolated from 7 DWD stations,  evaporation estimated with 3 different methods (Dalton, Energy-balance, Penman)

Qs,in : Surface inflow with SCS curve number method

Qs,outSurface ouflow: based on lake level and the digital elevation model (DEM)

Qgw,in-Qgw,outGroundwater (GW) balance calculated as unknown

Calculating evaporation from the lake surface according to the Energy-balance method shows a significantly increasing evaporation over the considered time period from 1960 - 2021 for montly and yearly values and an average yearly evaporation of 727 mm/a. The average yearly precipitation was calculated to be 578 mm/a and no significant trend could be observed. The differences in precipitation and evaporation lead to a partly strong negative yearly climatic water balance for the lake, which is calculated as yearly precipitation minus yearly evaporation. Calculating the groundwater balance shows positive values for most times, which means that more groundwater flows into the lake than out of the lake. The time series of the calculated groundwater balance does not show any significant trend in the monthly values, but a significantly increasing trend in the yearly values. The arithmetic mean for the groundwater net flow was calculated to be 9,58 mm/month (Ölmez, 2023).

Different evaporation estimates lead to very different groundwater and climatic water balances for Groß-Glienicker See:

  • Evaporation with Energy-balance: strong negative climatic water balance (WB), positive groundwater (GW) balance
  • Evaporation for water surfaces according to the Central Europe Refined analysis version 2 (CER v2): except for recent years positive climatic WB, negative GW balance
  • Evaportranspiration for forest according to the Central Europe Refined analysis version 2 (CER v2): fluctuating climatic WB and groundwater balance, in recent years negative

Most of the results have been generated within the student research project of Can Veli Ölmez (2023): Groß Glienicker See Ein Nulldimensionales Modell zur Ermittlung der Grundwasserbilanz

2. Hydraulic calculations to estimate potential water level increase in Sacrower See

Simplified hydraulic calculations as well as hydrodynamic simulations with Telemac 2D were carried out to investigate to which extend reopening the Schiffgraben could stabilize the level in Sacrower Lake. The water level time series of the river Havel close to the lake and of the Sacrower See have been compared to identify periods of positive water level differences, i.e. when the water level in the Havel was higher than in the lake. In the considered time period of 2012 - 2022, the maximum observed positive water level difference was approx. 24 cm. Hydraulic calculations have been carried out to investigate the needed time of balancing the water level in Havel and the Sacrower See by assuming that water can only flow from the Havel into the lake but not the other way round (by weir operations based on the given water level difference). Friction coefficients and channel dimensions have been varied to study the effect on the water transport time from the Havel into the lake. Result show, that the sensitivity of friction and considered channel width are relatively small and that the maximum potential water level increase in the lake of 24 cm could be reached for most configurations. The potential of increasing the lake's water level by reopening the Schiffgraben strongly depends on the given water levels in the river Havel and the lake. It could be shown, that most of the lake water level increase was generated during strong flood events.

Most of the results have been generated within the Bachelor thesis of Hendrik Blaese (2023): Hydraulische Berechnungen zum Wasseraustausch zwischen Havel und Sacrower See

Project head:

Prof. Dr.-Ing. R. Hinkelmann

Scientific assistant:

Dr.-Ing. Franziska Tügel

Project period:

January 2022 – December 2024

Funding:

Einstein Foundation Berlin

Study Area

Preliminary results for case study 3

Preliminary results for case study 1