Developments in climate scenarios – how relevant are they to KWR?

KWR does a lot of work in the field of climate adaptation – which technological developments help us to deal with a changing climate? – and also in generating insights that underline the need for mitigation – what are the consequences of global warming for the water cycle and our water supply? Climate science is (by necessity) a very active field of science, which is mature but certainly not yet fully developed. On Monday 16 November, the KNMI organised a workshop entitled ‘Towards new KNMI climate scenarios’, in which their researchers explained how evolving scientific insights are finding their way to a new collection of climate scenarios for the Netherlands to be published in 2023, as successors to the KNMI’s 14 scenarios. As a prelude to the new scenarios, the KNMI Climate Signal will be published at the end of 2021, providing a first indication for the Netherlands in the sixth IPCC Assessment Report. We took part in the workshop, seeking to learn what new trends and signals there are and what the new insights might mean for the water cycle and our research work.

The morning programme provided an overview of new dimensions and knowledge included in the scenarios in terms of heat, drought, precipitation, sea level and wind. The effects of urban heat islands on temperature and precipitation (also on the leeward side of a city) were mentioned. For consideration of drought the researcher in question indicated that models used represent NL+, i.e. the Netherlands supplemented with the foreign river basins of Rhine and Meuse. A new generation of climate models (H-Clim), with a higher resolution of 2.5 km per cell and including more physics, makes it possible to predict summer rainfall events well (in contrast to previous generations). These, combined with new scientific insights, lead to the conclusions that the scenarios will change slightly, with a decrease in average precipitation and an increase in extremes (think also of hail and gusts of wind). The models predict an increase in evaporation and an increase in precipitation, with a higher precipitation deficit in spring. A more stable stratification in the atmosphere may have a dampening effect on extreme precipitation, possibly making it less extreme than previously thought. However, these rare extreme events (long repetition time) may become more intense. What the new models also show is that the relationship between stability and temperature will be different for the future climate than for the current one. The science is still being developed. With regard to sea level rise, the KNMI will take a somewhat less conservative stance than the IPCC, which will probably (our conclusion) mean a higher sea level rise than previously predicted. This is being considered because none of the models predict the dramatic changes that we are now seeing on the ice caps. Regarding the question of whether the local sea level along the Dutch coast is rising as fast as the global average, the answer is ‘yes’. However, this is hidden in the observations due to a sharp decline in water surges/levels caused by wind. Over the course of the century, strong winds from the S-W direction will become more frequent, while calm days with little wind will also become more frequent. After a lunch break, 100 of the original 200 participants discussed various topics in 11 subgroups.

Andrew took part in the break-out sessions on heat (with Ben Wichers Schreur of KNMI), innovations in the Climate Effect Atlas (with Arjen Koekoek, Stichting CAS) and climate adaptive transitions (with Willem Ligtvoet, PBL). In the break-out session on Heat, there was a lot of discussion about methods of scaling down heat to the (sub)neigbourhood level. There are a lot of parameters to take into account for this kind of calculation, but in the end this is what it’s all about if you want to say something about e.g. the impact on health. With heat stress it’s all about apparent temperature indoors and (very different) outdoors, and the difference between day and night is also very important when it comes to apparent temperature. The necessary parameters are provided by the weather modules, but these have yet to be translated into wind chill and possible impact on health. In addition to the direct impacts, attention was paid to second-order effects such as pathogens for which the temperature is currently limiting in the Netherlands. Some pathogens, but also mosquitoes for example, can multiply faster with higher temperatures and milder winters. It is also important to assess the health effects of climate adaptation measures. For example, if we place rainwater storage tanks everywhere, this can cause health risks. Decoupling as a means against flooding was also mentioned. RIVM wants to map out these health risks.

With regard to the break-out session on the Climate Effect Atlas, the innovations were discussed and the main conclusion was to take a look at the new viewer that is now in the making.  This will include new maps, for example on subsidence and foundation problems.

The final break-out session on Climate and Transitions may be interesting for KWR’s new impact programme ‘Inclusive Water’. Water boards and municipalities need more clarity about where to expect extremes, and what the action perspectives are. Each water board now makes its own translation of the KNMI scenarios with its own hydrological models for its own area. Could that not be done more systematically? For insurance companies, for example, it is important to translate the scenarios properly into a shorter time scale, for example 20 years. And for the transitions, the specific application in the various sectors is important.  In the ‘Netherlands Later’ project the PBL, KNMI, Deltares and WUR will work on a Spatial Exploration 2022. This study will look at the interaction between climate adaptation, transitions in freshwater supplies (Delta Programme) and other transitions (including energy, agriculture and biodiversity). The aim is to identify a limited number of administratively relevant criteria as well as a monitoring system (measuring, knowing, acting).

What does this mean for our work at KWR? It is clear that the KNMI’23 scenarios will deviate from the KNMI’14 scenarios on a number of aspects. Earlier, the KNMI published a news report on their upwardly revised expectations regarding the duration, intensity and frequency of droughts in the course of this century. It is also clear that the insights are still evolving. This means that as KWR researchers we must keep a close eye on developments in climate sciences and continue to incorporate the latest insights into our work, in order to prevent our work from losing its relevance before long. In addition, it is important to understand that the future climate system may show different relationships between parameters than in the historical climate system – this means that we must be extra careful when applying machine learning models based solely on historical data. If KWR , in the ‘Inclusive Water’ programme, is going to look at the interaction between climate adaptation and other transitions, it will be valuable to seek the connection with other institutions (such as PBL). Above all, these developments mean that work remains to be done for KWR and fellow institutes!