Our ability to make long term predictions

Contributed by Bettina Schaefli, a HEPEX guest columnist in 2014


Mauvoisin dam in Switzerland

Almost ten years after my PhD on hydropower production and climate change, I just wrote a review on “Projecting hydropower production under future climates” for WIREs Water (1).

It was a very challenging exercise to synthesize the state-of-the-art at a moment in time when many hydrologists are fundamentally questioning our ability to make long term predictions.

What is actually the relevance of assessing hydropower climate change impacts in a world where “everything flows” (a reference to the recent IAHS Panta Rhei research initiative) and where the evolution of legal and socio-economic constraints is orders of magnitude faster than climate change?

And being aware of all uncertainties along the modelling chain of climate change impact assessment (fig. 1), should a hydrological modeller simply confess that everything is uncertain and that we are all agno-hydrologists (from the greek agnōsis, “not knowing”)?


Figure 1: Sketch of the model chain for climate change impact simulation on hydropower production. Many more feedback loops between the models could exist.

It’s obviously relatively easy to criticize any climate change impact study, especially if the study tries to analyze large catchments with complex infrastructure (see for example the discussion of a Swiss case study in HESSD). But on the other hand, as hydrologists, we have to provide input to policy and planning discussions.

My own PhD work (Horton et al., 2006Schaefli et al., 2007) entered political discussions, but was also considerably criticised by Swiss colleagues (for the simplified glacier evolution model and the handling of evapotranspiration). Looking back, I would not assign probabilities of occurrence anymore to projected annual runoff or to projected hydropower production. But the work had the merit of showing a range of plausible scenarios, which plays a certain role for the development of flexible infrastructure.

And during my work on the hydropower review, I became aware of another important role for hydrologists: to re-centre the analysis of future hydropower production to the scale at which it is reasonable to make projections – the catchment scale. I came across a range of global or continental scale analyses of hydropower potential with models that probably do not even contain rivers. Such results should definitively not be the basis for (not) taking action.

Despite of being highly uncertain, climate change impacts on hydropower production can certainly not simply be neglected in the planning of the energy turnaround in Europe, especially not with respect to potentially significant changes in the seasonal occurrence of extreme high or low flow events. But one strategy to cope with this is certainly to further develop real-time forecasting systems even for small hydropower production catchments.

(1) If you are interested to read the submitted review paper, just send me a message.


  1. Maybe our main challenge is how to manage expectations. Nobody can be expected to eliminate uncertainty, but any reduction thereof can result in tangible benefits to end users. In my experience, pointing that out is very helpful in removing the ‘certainty’ benchmark from the table.

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