Fig. 2. Conceptual framework of the challenges posed by different cases of flood event attribution, including possible solutions.

2.1 Non-linear relation between extreme precipitation and floods

Shifts in precipitation extremes are not clearly reflected in global flood observations (Berghuijs & Slater, 2023; Blöschl et al., 2017; Do et al., 2017; Kundzewicz et al., 2014; Slater et al., 2021; Zhang et al., 2022). To examine where trends of extreme precipitation and of extreme discharge converge and diverge in sign, we calculated significant trends in annual multi-day extreme precipitation based on the ERA5 climate reanalysis dataset (Harrigan et al., 2020), and in extreme discharge based on the dataset GloFAS, which is modelled based on ERA5 meteorological forcing (Hersbach et al., 2020), for the period 1979-2020 (Fig. 3). Although over most locations the sign of trends in discharge extremes matches that of precipitation extremes (orange and green colours), for many locations an increase in precipitation extremes is matched by a decrease in discharge extremes (blue). Locations where decrease in precipitation extremes is matched by an increase in discharge extremes (purple) are very rare.