Hans von Storch, Institute of Coastal Research 2018 Instationarity and time - the multiple challenges for deciding about adapation Hans von Storch, Institute of Coastal Research 25 min‘s  10 - 14 December 2018 - AGU Fall Meeting, Washington

An example: Planning for increased sea level in the port of Hamburg until 2080

Decisions on adaptation are dealing with a number of instationarities: What will change in the future? The geophysical state, which requires adaptation. In case of sea level – we know it is rising, but there is considerable uncertainty how fast it will rise. The knowledge about the dynamics and the expectations of the future change of the geophysical state In case of sea level: the uncertainty is presently high but will decrease in the coming decades Technological-organizational options for adaptation. Sea level: The range of options will increase, as long as now available options are not eliminated by instituting other usages. Societal preferences and needs: Sea level: The preferences will change, but it is unknown when and how.

Sea level change – present knowledge „Future sea level rise“ is an active field of research in climate science. The scientific knowledge has been reviewed and documented since 1990 in a series of assessments reports of THE IPCC. According to these reports, the expectations about future sea level rise varied from report to report, with considerable ranges of the rise until 2100, from a few decimeters to about 1 m. When in 2007 surveying members of the scientific community about the realism of the IPCC expectations, about half supported the assessment, while other half 50% adopted a critical position, of which 2/3 favored higher increases, and 1/3 lower. Ranges of expected global mean sea level rise at about 2100 according to the IPCC reports. © Conrad & Shephard. Opinions of climate scientists of the accuracy of the 2007 IPCC assessment about future sea level rise. A rating of 4 indicates a right assessment by IPCC, 1-3 an underestimation by IPCC, and 4-7 an overestimation. (Bray and von Storch, 2010)

Climate change: ongoing sea level rise in Hamburg For assessing the change in sea level in Hamburg, reports about the heights of tidal high water (THW) are available. (Note that changing tidal dynamics may lead to differences in the development of tidal high water and in mean sea level.) Until about 1960, THW in Hamburg was about 30 cm higher than in Cuxhaven (at the mouth of the river Elbe); since 1980 the difference amounts to about 60 cm. This change is attributed to anthropogenic changes in the morphology of the tidal river. Change of annual mean tidal high water in Cuxhaven and in Hamburg. Data provided by WSV Cuxhaven und by HPA.

Climate change: ongoing sea level rise in Cuxhaven The development of the mean sea level in the North Sea is represented by THWs as recorded by the tide gauge in Cuxhaven. The (annual) mean THW is steadily increasing, until about 1980, when the increase seems to be halted. Regional storminess is responsible for variations of THW on time scales shorter than a years. The intensity of variations (recorded as 99%iles of intra-annual variations of THW minus the annual mean) shows no systematic change. An increase of storminess cannot be detected at this time. The global mean sea level was increasing by about 1.1 mm/year until about 1990; thereafter the increase has accelerated to about 3.3 mm/year (Dangendorf et al., 2017). Temporal development of THW in Cuxhaven since 1900. The blue curve shows the annual mean THW, the development of which is a proxy for the mean sea level rise. The red curve shows the 99%iles of the intra-annual distribution of THW, after subtraction of the annual mean. This curve is a proxy for the change in regional storminess.

Climate change: Ongoing sea level rise in Hamburg Thus, the change of the local conditions in Hamburg depends on at least two factors namely the sea level in the North Sea and the anthropogenic changes of the river (shipping channel, coastal defense) There is a the discrepancy between the change of THW in Cuxhaven and the global mean sea level. The reason for this discrepancy is unknown. The mechanism of the GHG-related climate change suggests two characteristics of sea level rise. - a change which is somewhat delayed to the thermal effect. - a recently accelerated rise. Thus, the steady, non-accelerating rise of sea level at Cuxhaven can hardly be attributed mainly to global climate change. It may be that the lack of acceleration is related to the retardation of the sea level change following the thermal change. The change in global mean sea level is consistent with the explanation by steadily accumulating greenhouse gases in the atmosphere. More research, in particular more monitoring of the change in sea level in Cuxhaven and Hamburg are needed. This aspect of science is not yet settled.

Recommendations for adaptative measures in the port of Hamburg Having timing as a significant factor when assessing the suitability of any planning. At a later time, the knowledge about the challenges will be improved, more options will be available, and the public preferences will be more stable. Decisions about implementation of adaptation and details as late as possible without compromising safety etc. issues Planning of modernization such that future options for unexpected developments are conserved. Planning of building of infrastructure with a flexible expectation of future, time-dependent sea level rise. Employing a fixed time horizon, for the life time of new infrastructure. This depends on the type of infrastructure. Continue, or install, long-term monitoring of geophysical change. Construction of upper limits of conceivable time-dependent future change

Summary and outlook Any long-term planning of infrastructure and urban development needs to consider the aspect of adaptation. This includes the unfolding of the geophysical change but also the unfolding of new knowledge, of new options and new societal preferences. Thus, decisions about implementation of adaptation and details should be made as late as possible as safety and utility issues are not compromised. Planning of modernization should be done such that future options for dealing with unexpected developments are conserved. The case of Hamburg: The development of the sea level in Hamburg depends on at least two factors, the global sa level rise and anthropogenic modifications of the tidal river Elbe. High-end estimates of future sea level rise point to an increase of 25-50 cm in 50 years, to 60-170 cm in 2120, and 100-350 cm in 2220. The estimates for 2080 are somewhat robust, but those for 2120 and 2220 are questionable. Continued monitoring, consistent with past observations, is essential and must be available for planning purposes. Presently implemented modernizations and investments should be constrained so that later rectifications are possible – such as lifting bridges or heightening of flood gates.