Introduction

Within the framework of the German Strategy for Adaptation to Climate Change (DAS), the Federal government presents the 2023 (third) Monitoring Report on the German Strategy for Adaptation to Climate Change. This report describes the impacts of climate change on the basis of solid scientific data, at the same time as providing the public as well as decision-makers in all sectors of society with information on tangible impacts of climate change. The risks associated with climatic changes affect all sectors of society and all ecosystems which make up the foundations of our life in all aspects of its diverse structures and services. Consequently, the organisation of risk provisioning and adaptation capacities is a task that concerns society as a whole. Curbing global warming and its impacts is a core political challenge for the 21st century worldwide. Meeting this challenge is an essential prerequisite for achieving the objectives set by the 2030 UN Agenda with its focus on sustainable development^I.

In this light, the Federal government has, as early as 2008, under the auspices of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU), submitted the first German Strategy for Adaptation to Climate Change (DAS) which has been continuously developed further ever since. The overarching objective of DAS is to mitigate the vulnerability of ecosystems and society to the impacts of climate change, at the same time as increasing the resilience and adaptability of these systems. The work on DAS has been carried out within the Federal government under the auspices of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMUV) via the Interministerial Working Group for Adaptation to Climate Change (IMAA) with the cooperation of all Federal ministries and their scientific authorities linked to this Working Group. Furthermore, all work within the DAS framework is carried out in close cooperation with the Länder and municipalities.

Since 2021, the Federal government has been strengthening the political control of climate adaptation by undertaking the following:

• a federal law which establishes a binding legal framework for the adaptation to climate change,
• a precautionary climate adaptation strategy with measurable targets, and
• safeguarding the joint funding of precautionary climate protection and climate adaptation measures at Federal and Länder level.

Since 2008, there has been ongoing development work on a reporting system on DAS consisting of various components which are updated at regular intervals: Every four years, the DAS Monitoring Report provides updates on climate impacts and adaptation on the basis of measured data. Every six years, a Climate Impact and Risk Analysis (KWRA) is carried out analysing future climate risks. Evaluations of the DAS are carried out at regular intervals. These are the foundations for further developing the adaptation strategy covered in the DAS Progress Report and underpinned by an Action Plan (APA). In the years of 2015¹ and 2020² the Federal government presented progress reports accompanied by the 2015 and 2020 action plans.

With the aid of scientific indicators in respect of climate impacts and adaptation, the 2023 Monitoring Report imparts information on the 16 action fields incorporated in DAS. The 2021 Climate Impact and Risk Analysis (KWRA) was used to determine the 31 foremost and most urgent requirements for action in Germany in 2021³. The 2023 Monitoring Report presents new indicators for some of the most urgent requirements for action, thus facilitating the observation of developments on the basis of measured data. Compared to the first two Monitoring Reports, the structure has been developed further. Each action field is now preceded by an overview of what has been happening with regard to climate change and what has been done already. Furthermore, links are made to the KWRA analysis, and important gaps in respect of data and knowledge are pointed out. The technical foundations of the Monitoring Report are reinforced by cooperation with more than fifty authorities at Federal and Länder level, universities and professional organisations whose expertise contributes to the technical quality of the indicators and the reliability of the evaluation.

The DAS Monitoring Indicators convey a comprehensive overview of the kind of changes that can be attributed to climate change in Germany, and what kind of adaptation measures have already been implemented. The 2023 Monitoring Report furthermore provides evidence for precautionary efforts that have been made at Federal level in view of the increasing risks. At the same time, the close mutual dependence on achievements in respect of climate protection and progress regarding climate adaptation is also communicated. The only chance to limit and control the impacts of global warming is represented by the intensification of efforts in respect of climate protection. At the same time, the precautionary measures taken to adapt to climate change are both important and urgent, in the endeavour to counteract the impacts which have already become inevitable, and to find ways of mitigating any associated ecological, social and economic damage with the greatest possible efficiency.

The previous DAS Monitoring Report was issued in 2019. Since then, Germany has been confronted repeatedly with heatwaves, droughts, flash floods and flooding events. Even more strongly than in 2019, the impacts of global warming are reflected in the measured data contained in the 2023 Monitoring Report. The temperatures of air, water and soil have continued to rise, thus also increasing the impacts on humans, environment, economy and infrastructures.

Above all, the extreme events are engrained on the collective memory: From 12th until 15th July 2021, the low-pressure front Bernd caused extreme downpours in various parts of Western Europe. In the region encompassing the rivers Ahr and Erft in Rhineland-Palatinate and North Rhine-Westphalia, flash floods and flooding events resulted in disastrous damage and loss, including the loss of more than 180 lives in Germany – most of them in the Ahr valley. Overall, this caused insured material damage to residential property, household effects and business premises totalling 8.1 billion Euros (cf. Indicator BAU-I-5). To date, this has been the highest claims expenditure in terms of property insurance involving damage caused by natural hazards. The World Weather Attribution (WWA), an international alliance of individuals involved in scientific activity, researched the extent to which the occurrence of such extreme weather events is related to climate change. They reached the conclusion that the probability – of such extreme rainfall events being due to climate change. has increased by a factor of between 1.2 and 9⁴.

The Monitoring Report shows the following: Apart from heavy rain and flooding, there are other extreme events such as heat and drought that descended on Germany with all their measurable impacts. Summers with major heatwaves and highest measured air temperatures to date have been occurring more frequently; for instance, in July 2022, for the first time ever north of the 53rd parallel, at the station of Hamburg-Neuwiedenthal, a temperature in excess of 40 °C was measured⁵. In the years of 2018, 2019, 2020 and latterly in 2022, periods of great heat caused, in particular, stress to inhabitants of cities. In Berlin, Frankfurt am Main and Munich, hot days with daily peak temperatures of at least 30 °C and tropical nights with temperatures never dropping below 20 °C, occurred distinctly more frequently than in respect of the nationwide mean. Between 2018 and 2020, some 19,300 individuals died as a result of heat effects in Germany (cf. Indicator GE-I-2).

Heatwaves and droughts also led to functional restrictions with regard to infrastructures and waterways. For example, there were technical obstructions in goods and passenger transport as well as, in some areas, some massive restrictions to electricity generation in nuclear and coal-fired power plants in Germany and other member countries of the Trans-European Electricity Network. Owing to the high temperature of water sources, on one hand there was insufficient coolant water available, while on the other, coal supplies were restricted by low water levels prevailing in waterways used by inland shipping.

The years mentioned above which had remarkably hot summers, were also characterised by low precipitation levels which regionally led to severe droughts. As far as the water budget is concerned, massive losses were incurred between 2018 and 2020. Ever since the turn of the millennium, Germany has been losing 2.5 gigatonnes or cubic kilometres of water per year (cf. Indicator WW-I-1). In the years of 2019 to 2021, record shortfalls were recorded at gauging stations in terms of long-term lowest groundwater levels. The effects of the drought years have not yet been offset even as late as 2023. Insufficient availability of soil water has led to yield losses in agriculture. Owing to drought stress and associated infestations with beetles, there has been a significant increase in crown defoliation. From 2019 onwards, it has become obvious that dieback rates of trees has been skyrocketing with regard to all tree species. The extremely dry weather pattern has also been reflected in the forest fire scenario. There were considerably more and – in the north-eastern Länder – large-scale forest fires.

Despite the drought – especially during the summer half-year of recent years – there were several, partly extreme flooding events in some regions. On those occasions, the multi-annual mean flood discharge values were exceeded by several multiples at some gauges. In fact, the apparent contradiction between drought and extreme flooding represents a genuine example of cause and effect: On one hand, warmer air absorbs more moisture, thus increasing the risk of heavy rain; on the other, it increases the frequency of drought phases. To name just one of the consequences: Desiccated soils are unable to absorb or store the water accumulating in a heavy rainfall, thus leading to rainwater running off the surface which results in river levels rising rapidly and bursting their banks.

Indicators

For the 2023 (third) Monitoring Report, the indicator system dating back to 2019 was reviewed and developed further. As a result of the current update, the DAS Monitoring Indicator system comprises 117 monitoring indicators in total: 67 indicators describe the impacts of climate change (Impact Indicators), 45 describe adaptation measures or activities and conditions supporting the adaptation process (Response Indicators), while another 5 are cross-sectional monitoring indicators

64 Indicators stemming from the 2019 Monitoring Report were updated based on the same methodology. 25 Indicators were revised on the basis of new scientific findings and / or changed baseline data. They are therefore presented in an altered form, although most of these appear under the same indicator title as before. 15 Indicators were deleted from the set, either because the relevant data sources no longer exist or it was possible to replace those indicators by others, or because it is no longer possible to illustrate the subject matter adequately by means of the data available. Most of the deletions (5 indicators each) used to appear in the ‘energy industry’ and ‘tourism industry’ action fields respectively. In those cases, there were question marks regarding the previously illustrated close relationships between the circumstances involved and climate change. 4 indicators were assigned a dormant status, as it is still not possible to update the indicators in question compared to their status in the 2015 report, and / or because methodical reviews are imminent. It is expected that these indicators will reappear in the 2027 Monitoring Report (possibly in an altered form). 28 indicators were newly created and make their first appearance in the 2023 Monitoring Report. Innovations are contained in nearly all action fields. The new indicators either replace indicators that have been removed from the set, or they address new themes which had not been examined before within the framework of the monitoring system. These indicators expand the thematic bandwidth and enhance the quality of the illustrations.

As far as the ‘water balance and water management’ action field is concerned, the work on the review and development of new indicators was carried out in close cooperation with experts at Federal and Länder level within the climate indicator subgroup which is part of the Federal / Länder ‘water working group’ LAWA. This group – appointed by the Standing Committee on Climate Change (LAWA-AK) – was tasked with bringing about a cross-Länder agreement on indicators which would allow the illustration of climate change impacts on issues pertaining to the water sector. Within the framework of a research project (DASIF) conducted on behalf of the Federal Environment Agency (UBA), three indicators – based on satellite data – were newly developed, to replace previous case-study indicators (see below), thus permitting to make statements on the situation nationwide. Within the framework of a broader UBA project, an indicator on the ‘soil’ action field was newly developed and incorporated in the new DAS indicator set.

Principally, all monitoring indicators are intended to illustrate, by means of time series, developments across the whole of Germany. In respect of thematic aspects which are not yet sufficiently underpinned by nationwide data to allow the creation of indicators, it was possible in some cases to develop case studies. In the 2023 Monitoring Report, 13 such case studies demonstrate by means of spatially limited data sets, what statements might be generated at the nationwide scale if the relevant data were available. In respect of the 2023 Monitoring Report, it was possible to develop indicators further – which in the 2019 Monitoring Report had been case-study indicators – thus permitting to include them in the current Monitoring Report as indicators of nationwide validity.

Regional differentiations in respect of indicator illustrations are not generally provided for in the nationwide Monitoring Report. However, in some individual cases, nationally averaged statements are difficult to interpret. With the aid of time series for individual wider areas (such as ‘north’ or ‘south’) it may be possible to provide more specific statements subject to the availability of relevant data. Map illustrations are a new feature now integrated in the 2023 Monitoring Report. These maps supplement the illustrations pertaining to time-series with regional differentiations for a specific time period.

The deadline for updating the time series in the current, that is to say. the third Monitoring Report was 30th September 2022. It follows that principally, the last-named date in the indicator charts refer to the year 2021. Wherever this seemed either meaningful or necessary, the report texts provide a prospect of developments in 2022.

Handling uncertainties

It is not possible to illustrate all relevant climate impacts and adaptation activities by means of quantitative monitoring indicators. Several processes of data collection are still in their initial stages. However, extended time series will be required before it is possible to interpret any relevant developments. The unavoidable limitations in terms of the availability of data also mean that the number of monitoring indicators used currently in action fields does not necessarily reflect their importance.

In respect of numerous monitoring indicators, it is possible to provide a qualitative description of causal relationships between observable changes in the environment, society or economy on one hand and climate change on the other. However, it is much more difficult to determine their significance, as ecological and societal systems are influenced by multiple factors. When assessing damage to forests, for example, it is necessary, in addition to any impacts of climate change such as seasonal heat or drought periods or severe storms, to take into account other impacts not related to climate change, such as nutrient inputs, acidification and high ozone concentrations which may impact the health of trees. Intense discussions have taken place (and are likely to continue) in the course of the (further) development of the DAS Monitoring indicator system regarding cause-and-effect-relationships, and during the work on adapting indicators to the latest state of the art.

Fuzzy interpretations can also occur in respect of adaptation measures. Numerous measures such as the operation of the heat warning service provided by DWD, have been taken specifically in the interest of climate adaptation. Other measures also contribute to adaptation but that is not their only purpose. For example, nature-oriented measures such as forest transformation or the greening of buildings have multiple positive effects for which they have been planned and implemented in the first place. In any case, these measures also support an effective adaptation process.

In view of the inevitable uncertainties and a degree of fuzziness as discussed above, the intention is to continue reviewing and redeveloping the monitoring indicator system in the course of future updating cycles.

Assessing the developments

DAS Monitoring Indicators are intended to facilitate an assessment of developments that have been observed. The benchmark is the DAS objective to reduce the vulnerability to climate change impacts and to maintain and augment the adaptability of natural and social systems to the inevitable impacts of climate change. The intention is that the political objectives outlined in various action fields can be maintained even when faced with changes in the climatic framework conditions.

The adaptation objectives are currently the subject of a wide-ranging process of discussions. The adaptation targets are currently undergoing a wide-ranging discussion process which aims at the development of quantified targets. The achievement of those targets should be tangibly verifiable by means of indicators, some of which may have to be newly developed. The future development of the DAS Monitoring Indicator system will include the integration of these new indicators. As far as the current monitoring indicators are concerned, there have been no quantified targets set so far, which would make an assessment of the time series possible. The assessment is restricted to the outcomes of a statistical trend analysis and an appraisal examining whether the trend is basically in line with DAS objectives. Nevertheless, a negative or positive appraisal of trends does not seem meaningful in all cases, as the consequences of the changes observed are not always fully known. For example, an earlier flowering of winter rapeseed as a consequence of climate change, indicates that climate change does impact agricultural cultivation. However, the earlier flowering is not in itself necessarily a positive or negative phenomenon as it is part of ecological relationships and dependences. In cases of this kind, the illustration is restricted purely to the outcome of the trend analysis without having been subjected to an appraisal.

In respect of their trend developments, the time series were classified within the framework of statistical trend analysis. Each trend analysis was carried out using the same statistical process for all indicators. The methodology underlying the process applied in respect of the 2019 Monitoring Report was further developed. The analysis was applied to both linear (rising and falling) trends and to trends with trend reversal (square trends) respectively. Trend reversal is useful – especially when observing extended time series – for describing developments which started out as negative trends but, owing to successful adaptation measures, have recently become positive, or vice versa. The analysis of linear trends is carried out for all time series from 7 data points onwards, whilst for square trends, it is carried out from 13 data points onwards. In the process of trend analysis, all data points of the available time series are taken into account. Any data series with insufficient data points or which are based on surveys that are irregular or too far apart temporally are eliminated from analysis. In addition, a statistical change analysis is now carried out additionally for data series with at least 30 data points. This type of analysis checks time series for any significant discontinuities or changes in the development. Basically, all data points of a time series are always entered into the trend analysis. In cases where indicators illustrate time series of different lengths, it follows that the comparison of the trends obtained is limited by this fact. For methodological details regarding trend analysis, please consult the Organisation Manual for DAS Monitoring (Organisationshandbuch zum DAS Monitoring).

^{I - United Nations General Assembly Resolution dated 25th Septem­ber 2015 ‘Transforming our world: the 2030 UN-Agenda for Sustainable Development’ (https://documents.un.org/doc/undoc/gen/n15/291/89/pdf/n1529189.pdf). Goal 13 stipulates to ‘Take urgent action to combat climate change and its impacts’, and to ‘Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries’}

^{1 - Die Bundesregierung (Hg.) 2015: Fortschrittsbericht zur Deutschen Anpassungsstrategie an den Klimawandel. Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit. 275 pp. https://www.bmuv.de/fileadmin/Daten_BMU/Download_PDF/Klimaschutz/klimawandel_das_fortschrittsbericht_bf.pdf}

^{2 - Die Bundesregierung (Hg.) 2020: Zweiter Fortschrittsbericht zur Deutschen Anpassungsstrategie an den Klimawandel. 61 pp. und Anhänge. https://www.bmuv.de/fileadmin/Daten_BMU/Download_PDF/Klimaschutz/klimawandel_das_2_fortschrittsbericht_bf.pdf}

^{3 - UBA – Umweltbundesamt (Hg.) 2022: Die Risiken des Klimawandels für Deutschland – Ergebnisse der Klimawirkungs- und Risikoanalyse 2021 sowie Schlussfolgerungen der Interministeriellen Arbeitsgruppe „Anpassung an den Klimawandel“. Dessau-Roßlau, 19 pp.
https://www.umweltbundesamt.de/sites/default/files/medien/376/publikationen/2022_fachbroschure_die_risiken_des_klimawandels_fur_deutschland_220218.pdf}

^{4 - Tradowsky J. S., Philip S. Y., Kreienkamp F., Kew S. F., Lorenz P., Arrighi J., Bettmann T., Caluwaerts S., Chan S. C., Cruz L. de, Vries H. de, Demuth N., Ferrone A., Fischer E. M., Fowler H. J., Goergen K., Heinrich D., Henrichs Y., Kaspar F., Lenderink G., Nilson E., Otto F. E., Ragone F., Seneviratne S. I., Singh R. K., Skålevåg A., Termonia P., Thalheimer L., van Aalst M., van den Bergh J., van de Vyver H., Vannitsem S., van Oldenborgh G. J., van Schaeybroeck B., Vautard R., Vonk D., Wanders N. 2023: Attribution of the heavy rainfall events leading to severe flooding in Western Europe during July 2021. Climatic Change, 176 (7): 1-38.}

^{5 - DWD – Deutscher Wetterdienst (Hg.) 2022: Klimatologischer Rückblick Sommer 2022. https://www.dwd.de/DE/leistungen/besondereereignisse/temperatur/20220921_bericht_sommer2022.pdf}