Measuring climate change

The Department of Geography at Kiel University and a Hamburg-based environmental data service provider supply indicators and algorithms for the “German Strategy for Adaptation to Climate Change” (Deutsche Anpassungsstrategie an den Klimawandel – DAS)


How can the effects of climate change in Germany be measured and assessed objectively to derive measures? The Federal Government’s “German Strategy for Adaptation to Climate Change” (Deutsche Anpassungsstrategie an den Klimawandel – DAS) wants to answer this question since 2008. In a first phase,  the strategy’s focus was on determining scientifically based indicators that are closely linked with effects of climate change. These are to be used to evaluate climate change itself (impact) as well as measures for adapting to climate change (response) over longer periods of time. Two evaluation reports have been presented so far, each one further developing and refining indicators and measures. A team of Kiel University (CAU) and Brockmann Consult GmbH has been commissioned to prepare more detailed information on five selected focus areas for the next series of reports. Their project entitled “DASIF – Operationalisierung von Indikatoren der Deutschen Anpassungsstrategie Klimawandel mit Fernerkundungsdaten” (DASIF - operationalisation of indicators of the German Strategy for Adaptation to Climate Change using remote sensing data) began in December 2019. During this project, the most prominent innovation is that satellite data from the Copernicus programme is to be used for the first time in DAS.  

Blue-green algae pollution in bathing waters (1), ice cover (2) and water temperature (3) of lakes and the occurrence of spring algal blooms in lakes (4): these four indicators can help to illustrate the continuous progression of climate change. They are what is known as impact indicators and form the focus of the research project DASIF. Another topic covered by the project is the green roof area of public buildings. As what is known as a response indicator, this can be used to assess the effectiveness of certain adaptation strategies. “To date there have only been individual case studies on these subjects,” explained Natascha Oppelt, scientific head of the DASIF project and Professor of Physical Geography at Kiel University. “At European level, by contrast, there has already been a lot of development on water body indicators and this can be implemented here nationally in a climatological context,” added Kerstin Stelzer, Head of Geoinformation Services at Brockmann Consult, who is responsible for the analysis of blue-green algae and spring algal blooms. With the aid of satellite data, the team around Natascha Oppelt and Kerstin Stelzer plans to research these five subject areas in greater detail.

New scientific ground

The Kiel-based and Hamburg-based experts on earth observation and modelling are using remote sensing data to look very precisely at, for instance, how much chlorophyll is in the water: “We can draw conclusions from this about algae growth in lakes,” said project manager Dr Katja Kuhwald. Thermal images in turn provide information on temperature changes and ice cover. “The accuracy and level of detail of the satellite data is impressive. It offers us spatial and temporal surveillance of lakes that is not possible at this level of detail through what are known as in situ investigations.”

The challenge, however, is that these indicators are intended to work for the whole of Germany, even though conditions vary significantly across Germany. “For this reason, we have to find a way to depict large landscape units. At the same time, we have to generalise results without losing their significance,” added Natascha Oppelt.

The scientists are testing various approaches to this. Classification into various types of lake according to location and size can be useful, for example. Alternatively, different landscape types, for example, the Alpine Foreland, the Central Uplands or the Northern Lowland, can be used as units. Data from in situ investigations by individual federal states (Bundesländer) and meteorological data are also incorporated into the development of indicators. And, of course, national and international experts are also consulted on the five subject areas. “Our Finnish colleagues, for example, are very good at researching ice cover. In Switzerland and in Sweden there is outstanding expertise on the subject of algae growth,” said Natascha Oppelt, listing examples. Data also needs to be collated at optimal intervals: will assessments be monthly, quarterly or annually? “That means a lot of trying out and optimising,” said the geographer. 

Transfer to practice

The scientific findings have to be converted into algorithms in order to be recorded as application-ready indicators in the DAS report in 2023. This will be done by the project partner Brockmann Consult GmbH: “The conversion of scientific algorithms into operational systems is an important component of our project,” said Kerstin Stelzer of Brockmann Consult. The algorithms for retrieving the indicators must be able to be automated. This requires professional software and a processing environment that produces analysable climate-relevant indicators from the very large data volumes derived from daily satellite recordings. It is also important for products and formats to be well defined so that integration into subsequent work processes can function smoothly. This process is also supervised by scientists in order to monitor the quality of the results. Stelzer says: “There may be some iterations in this process until all the requirements are met.”

The project was commissioned by the German Environment Agency (Umweltbundesamt, UBA) and funded by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) (research code 3719 48 101 0).

© Copernicus data (2019)

The research team uses remote sensing data to create consistent time series from which four impact indicators can be determined for the whole of Germany.

satallite pictures
© Copernicus data (2019), © U. S. Geological Survey

The ice-covered “Große Alpsee” lake near Immenstadt in February 2019 taken from the perspective of five different satellite sensors. It is possible to separate ice and water using these sensors. The Kiel-based team uses various sensors to calculate as accurately as possible how long the lake was covered in ice.

satallite pictures
© U. S. Geological Survey

Left: water temperatures on the surface calculated using thermal satellite data. The temperature in Lake Plön varied between 10 and 22 degrees Celsius on 20 April 2011. Centre: the temperature at the centre was 13.6 degrees Celsius. Right: the entire archive from Landsat satellites is used to track the change in water temperature in Lake Plön since the mid 1980s.


Professor Natascha Oppelt
Department of Geography at Kiel University
Head of EOM - Earth Observation and Environmental Modelling
+49 (0)431/880 3330


Dr Katja Kuhwald
Department of Geography at Kiel University
+49 (0)431/880-5642


Kerstin Stelzer
Brockmann Consult GmbH
+49 (0)40 696 389 307


Claudia Eulitz
Head of Press, Digital and Science Communication