Compound Extreme Events in Hamburg, Germany: A Flood Risk Assessment
(2026) In Master Thesis in Geographical Information Science GISM01 20261Department of Earth and Environmental Sciences (MGeo)
Dept of Physical Geography and Ecosystem Science
- Abstract
- Floods account for the majority of disasters caused by natural hazards worldwide, and their frequency and intensity are set to increase further as a result of climate change. To protect people and property, protective measures such as dykes and drainage systems are put in place. However, events that are often overlooked in this context are compound floods, in which several types of flooding occur simultaneously. This is also the case in the German city of Hamburg, which is used as the study area for this paper. The aim of this study is to determine the risk of compound flooding caused by heavy rainfall and storm surges and to compare it with the risk of the individual extreme events.
The methodology applied for this purpose is two-fold:... (More) - Floods account for the majority of disasters caused by natural hazards worldwide, and their frequency and intensity are set to increase further as a result of climate change. To protect people and property, protective measures such as dykes and drainage systems are put in place. However, events that are often overlooked in this context are compound floods, in which several types of flooding occur simultaneously. This is also the case in the German city of Hamburg, which is used as the study area for this paper. The aim of this study is to determine the risk of compound flooding caused by heavy rainfall and storm surges and to compare it with the risk of the individual extreme events.
The methodology applied for this purpose is two-fold: first, a flood frequency analysis is carried out, in which the intensities of a storm surge, a heavy rainfall event and a compound event with a return period of 100 years are determined based on historical time series. In the second step, the hydrodynamic model LISFLOOD-FP is used to simulate the resulting flooding for the three scenarios. Various input files, including a DEM and information on surface roughness, are used to calibrate the model to the study area.
The results show that the flood risk of the compound event is significantly higher than that of the individual extreme events. Extensive flooding occurs in low-lying areas and along the river. This is due to the coastal backwater effect whereby the high water level of the river during the storm surge prevents rainwater from draining away, causing it to accumulate in the city.
The results of this study underscore the need to integrate compound flooding into flood management in Hamburg and comparable cities worldwide. (Less) - Popular Abstract
- Floods are among the most destructive natural disasters worldwide, and climate change is making them even more severe. To protect cities, engineers build dykes against the sea and underground drainage systems to carry away rainwater. However, traditional disaster plans often fail to consider compound flooding, which refers to situations where different types of flooding occur together. This study investigates this phenomenon for the German metropolis of Hamburg. The city is faced with two threats: severe storm surges from the North Sea and heavy rainfall from above.
To find out what happens when both occur simultaneously, a two-step approach was used. First, historical data was analysed to determine the magnitude of a storm surge, the... (More) - Floods are among the most destructive natural disasters worldwide, and climate change is making them even more severe. To protect cities, engineers build dykes against the sea and underground drainage systems to carry away rainwater. However, traditional disaster plans often fail to consider compound flooding, which refers to situations where different types of flooding occur together. This study investigates this phenomenon for the German metropolis of Hamburg. The city is faced with two threats: severe storm surges from the North Sea and heavy rainfall from above.
To find out what happens when both occur simultaneously, a two-step approach was used. First, historical data was analysed to determine the magnitude of a storm surge, the amount of rainfall, and the nature of a compound event that, statistically speaking, occur once every 100 years. Second, these extreme scenarios were fed into a computer simulation of Hamburg’s terrain to see exactly how the water would flow.
The simulations reveal that when a storm surge and heavy rain collide, the resulting flood is significantly worse than if either event happened alone. The main reason for this is the so-called coastal backwater effect. During a storm surge, the water level in the Elbe River rises so high that it blocks the drainage. Instead of flowing into the river, the rainwater has nowhere to go and therefore causes extensive flooding in low-lying areas and along the river and canals.
The findings send a clear warning to urban planners. Evaluating flood risks in isolation leaves cities dangerously unprepared. To ensure future resilience, cities like Hamburg must urgently upgrade their flood defence strategies to prepare for the impending threat of compound flooding. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/student-papers/record/9226604
- author
- Krohn, Iris LU
- supervisor
- organization
- course
- GISM01 20261
- year
- 2026
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Geography, Geographical Information Science (GIS), Flood Frequency Analysis, Hydrodynamic Model, Compound Flood, Physical Geography, Storm Surge, Heavy Rainfall
- publication/series
- Master Thesis in Geographical Information Science
- report number
- 212
- language
- English
- id
- 9226604
- date added to LUP
- 2026-05-22 13:00:20
- date last changed
- 2026-05-22 13:00:20
@misc{9226604,
abstract = {{Floods account for the majority of disasters caused by natural hazards worldwide, and their frequency and intensity are set to increase further as a result of climate change. To protect people and property, protective measures such as dykes and drainage systems are put in place. However, events that are often overlooked in this context are compound floods, in which several types of flooding occur simultaneously. This is also the case in the German city of Hamburg, which is used as the study area for this paper. The aim of this study is to determine the risk of compound flooding caused by heavy rainfall and storm surges and to compare it with the risk of the individual extreme events.
The methodology applied for this purpose is two-fold: first, a flood frequency analysis is carried out, in which the intensities of a storm surge, a heavy rainfall event and a compound event with a return period of 100 years are determined based on historical time series. In the second step, the hydrodynamic model LISFLOOD-FP is used to simulate the resulting flooding for the three scenarios. Various input files, including a DEM and information on surface roughness, are used to calibrate the model to the study area.
The results show that the flood risk of the compound event is significantly higher than that of the individual extreme events. Extensive flooding occurs in low-lying areas and along the river. This is due to the coastal backwater effect whereby the high water level of the river during the storm surge prevents rainwater from draining away, causing it to accumulate in the city.
The results of this study underscore the need to integrate compound flooding into flood management in Hamburg and comparable cities worldwide.}},
author = {{Krohn, Iris}},
language = {{eng}},
note = {{Student Paper}},
series = {{Master Thesis in Geographical Information Science}},
title = {{Compound Extreme Events in Hamburg, Germany: A Flood Risk Assessment}},
year = {{2026}},
}