Processes and controls of regional floods over eastern China

Abstract. Mounting evidence points to elevated regional flood hazards under a changing climate, but existing knowledge about their processes and controls is albeit limited. This is partially attributed to inadequate characterizations of the spatial extent and potential drivers of these floods. Here we develop a machine-learning based framework (mainly including the density-based clustering algorithm DBSCAN and conditional random forest model) to examine the processes and controls of regional floods over eastern China. Our empirical analyses are based on a dense network of stream gauging stations with continuous observations of annual maximum flood peak (i.e., magnitude and timing) during the period 1980–2017. A comprehensive catalog of 318 regional floods is developed. We reveal a pronounced clustering of regional floods in both space and time over eastern China. This is dictated by cyclonic precipitating systems and/or their interactions with topography. We highlight contrasting behaviors of regional floods, in terms of their spatial extents and intensities. These contrasts are determined by fine-scale structures of flood-producing storms and anomalous soil moisture. While land surface properties might play a role in basin-scale flood processes, it is more critical to capture spatial-temporal rainfall variabilities and soil moisture anomalies for reliable large-scale flood hazard modeling and impact assessments. Our analyses contribute to flood science by better characterizing the spatial dimension of flood hazards and can serve as basis for collaborative flood risk management under a changing climate.