2. Challenges to flood event attribution

We argue that two main challenges limit our capacity to accurately attribute river flood events (Fig. 2): 1) Extreme flooding relates to the triggering precipitation event in highly non-linearly ways, because of the mediating hydrological and hydrodynamic processes. 2) Changes to the hydrological systems have occurred during the period of climate change, adding their influence on the occurrence of floods. These changes include natural and human changes in land cover, other human hydrological interventions, and the geomorphic responses of the river channel. In this section we examine these two challenges.