Understanding multidecadal variability for energy system studies: can current 20th century reanalyses do the job?

The variability of renewable power generation is often quantified based on modern reanalyses such as ERA5 or MERRA-2 which provide climatic information over the last few decades. Compared to infrastructure lifetimes, modern reanalyses cover only short periods and may consequently fail to sample relevant longer-term climate variability. While there is evidence for multi-decadal variability in wind power generation [Wohland et al. (2019), Zeng et al. (2019)], hydropower [Bonnet et al. (2017)] and solar energy [Sweerts et al. (2019)], a consistent treatment of multi-decadal variability has not been achieved. 

This knowledge barrier can potentially be overcome using 20th century reanalyses which provide internally consistent fields of energy-relevant variables (e.g., solar radiation, precipitation, temperature and wind). However, the provision of reliable climatic information on these timescales is known to be a challenge due to, for example, the evolution of measurement techniques. Some cases of spurious trends and other shortcomings of the datasets are known. It is therefore of utmost importance to quantify uncertainties prior to usage in energy system studies. To this end, we systematically compare 20CRv3, 20CRv2c, CERA20C and ERA20C with respect to variables needed in renewable energy assessments and report similarities and discrepancies accross the datasets. The focus is given to substantial differences with respect to multi-decadal solar radiation variability in Europe, also known as dimming and brightening. 

References

Bonnet, R., Boé, J., Dayon, G. & Martin, E. Twentieth-Century Hydrometeorological Reconstructions to Study the Multidecadal Variations of the Water Cycle Over France. Water Resour. Res. 53, 8366–8382 (2017).

Sweerts, B. et al. Estimation of losses in solar energy production from air pollution in China since 1960 using surface radiation data. Nat Energy 4, 657–663 (2019).

Wohland, J., Omrani, N. E., Keenlyside, N. & Witthaut, D. Significant multidecadal variability in German wind energy generation. Wind Energ. Sci. 4, 515–526 (2019).

Zeng, Z. et al. A reversal in global terrestrial stilling and its implications for wind energy production. Nat. Clim. Chang. (2019).