Sensitivity of bias adjustment methods to low-frequency internal climate variability over the reference period: an ideal model study

• Published in: Environmental Research: Climate
• Main Authors: Bonnet, Rémy, Boucher, Olivier, Vrac, Mathieu, Jin, Xia
• Other Authors: European Union, CNRS, Sorbonne Université, Ecole Polytechnique, CNES, ANR
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: IOP Publishing 2022
• Subjects: North Atlantic
• Online Access: http://dx.doi.org/10.1088/2752-5295/ac6adc; https://iopscience.iop.org/article/10.1088/2752-5295/ac6adc; https://iopscience.iop.org/article/10.1088/2752-5295/ac6adc/pdf

Abstract Climate simulations often need to be adjusted before carrying out impact studies at a regional scale. Technically, bias adjustment methods are generally calibrated over the last few decades, in order to benefit from a more comprehensive and accurate observational network. At these timescales, however, the climate state may be influenced by the low-frequency internal climate variability. There is therefore a risk of introducing a bias to the climate projections by bias-adjusting simulations with low-frequency variability in a different phase to that of the observations. In this study, we developed a new pseudo-reality framework using an ensemble of simulations from the IPSL-CM6A-LR climate model in order to assess the impact of the low-frequency internal climate variability of the North Atlantic sea surface temperatures on bias-adjusted projections of mean and extreme surface temperature over Europe. We show that using simulations in a similar phase of the Atlantic Multidecadal Variability reduces the pseudo-biases in temperature projections. Therefore, for models and regions where low frequency internal variability matters, it is recommended to sample relevant climate simulations to be bias adjusted in a model ensemble or alternatively to use a very long reference period when possible.