Soil moisture: A future key to predict heat waves

“Our first results on soil moisture were published in November last year. Here Akilesh Nair and colleagues showed the importance of soil moisture in climate predictions. Building on this, we can now predict major heatwaves several weeks in advance”, Professor Noel Keenlyside says. 

The predictions come from adding information about the soil moisture into the Norwegian climate prediction model (NorCPM). This is one of many interesting and societally relevant results and possibilities that the NorCPM, developed under the Bjerknes climate prediction unit (BCPU), can produce.  

Professor Keenlyside, principal investigator of the BCPU, explains that they used satellite’s measurements of the soil’s water content to adjust the climate prediction model, and saw that they could predict events like the 2018’s European’s summer heat wave that had major consequences in Norway. “This is because dry soil is a precondition for major heat waves, as with wet soil, energy is consumed by evaporation, inhibiting surface warming” he expounds. 

The major outcome of a major project 

NorCPM is, for Professor Keenlyside, the major outcome of the BCPU. Funds from the Trond Mohn Research Foundation had a huge impact. It let them bring a team together, for long enough to be able to set up the BCPU and develop the prediction model.  

Now, NorCPM allows them to make quasi-operational predictions, forecasting climate change from weeks to decades and at regional scales. The BCPU project will continue studying and analyzing data, working to enhance the model and collaborating with national and international institutions, taking on new challenges. 

Debate on two factors 

One of those challenges arises from the debate on why there was a cooling period between the 1940s and the 70s, and a little temperature pause around the late 90s. For this, there are two hypotheses, according to Keenlyside. One is that an “external force”, the aerosols, were the cause. The other is the effect of the ocean circulation in combination with the atmosphere. The influence of these factors is very important for understanding decadal fluctuations. As professor Keenlyside says: “what will happen over the next 10-15 years will depend a lot on what is the relative importance of these two terms".

Adding life to the model 

The biogeochemistry side of the global processes is a very important factor required to build a strong prediction model. This was the first task of researcher Filippa Fransner when she joined BCPU, to activate the biogeochemical module of NorCPM. By doing that, they unlocked the ability to predict factors beyond the physical climate, for example: phytoplankton. 

Fransner published a paper about using the model to predict the amount of phytoplankton in the Barents Sea five years in advance. This opens the door to additional applications of the predictions because phytoplankton, in her words “are the base of the marine food web. The reasoning is that, if we can predict the phytoplankton abundance, maybe that means also that we can predict even higher trophic levels. For example, fish”. 

There is yet much work to be done to, piece by piece, increase the realism of the prediction model. To get there, nowadays Fransner and her colleagues are working with interactive atmospheric CO2, by running  NorCPM in emission driven mode. She explains: “we let the model simulate the atmospheric CO2 itself and that depends on the fluxes between the air and the ocean, and the air in the land”. Moreover, its results contribute to the Global Carbon Budget, a project that integrates knowledge of greenhouse gases. 

Decadal predictions to get people’s attention 

The use of models allows us to preview what the future climate might be like. The models also make us able to see the climate processes that were and are now in action, and how they might change the climate.  

Researcher and leader of the data assimilation team at BCPU, François Counillon, thinks that decadal predictions are a better way to help people to understand this: “Un, which is useful for raising awareness of the importance of taking mitigation action now, and for stakeholders to plan mitigation actions and enhance profit”, adding “the standard climate reports typically present what will happen in 2100. This time window is often abstract for people and not useful for companies”. 

About the relevance of BCPU, Counillon says “BCPU has been instrumental in the development of NorCPM. We have now brought capacity to use observations for all of the Earth System Component (ocean, sea ice, atmosphere and land), which means that we can tell with even more accuracy what will happen in the near future”. 

The team keeps working on further developing the tools for the Norwegian climate prediction model and has started to use machine learning to emulate high-resolution model versions and gain in efficiency. They feel now better prepared for next year’s participation in the Coupled Model Intercomparison Project (CMIP), an international climate modelling project coordinated by the World Climate Research Programme (WCRP). In this event, all the different modelling institutes compare simulations to help to evaluate climate models in order to improve them. The data is free to use and available on its platform. 

How to take it to the next level 

The fourth area of BCPU is to help to make the predictions available and useful. “(climate prediction) provides information about how the future climate state will be and it can be used for lots of different applications. But one of the challenges with using this information is, from a researcher’s perspective, we don't know how useful information would be to a user and how they would actually apply it in their decision- making. So, this is a whole process that Climate Futures is undertaking”- Professor Keenlyside comments.  

Climate Futures is a centre for research-based innovation that works with companies, public organizations and research groups to co-develop better methods and practices for climate risk management.  

Apart from this, the predictions also contribute to the reports of the Global Annual to Decadal Climate Updates of the World Meteorological Organization (WMO). 

The BCPU funding from Trond Mohn is now finished, but the BCPU team has secured funding for the next years to keep improving the understanding of the climate processes and enhancing the predictions.