Are Pluvial and Fluvial Floods on the Rise?

ABSTRACT

The aim of this paper is accurately framed in its title Are pluvial and fluvial (river) floods on the rise? First, physical mechanisms that drive changes in hazard of pluvial and fluvial floods were examined. Then, a review of literature was undertaken on detection and an attribution of changes in hazard of pluvial and fluvial floods in observation records for past to present, as well as in model-based projections for the future. Various aspects, factors, processes and mechanisms, as well as various indices of interest were considered. There is quite a common, even if not scientifically justified, belief that, generally, floods are on the rise. However, in this paper, a balanced, knowledge-based assessment was undertaken, with discussion and interpretation, including caveats and indicating considerable departures from such a flat-rate statement. Observation records show that precipitation extremes have been intensifying on a global scale and for many regions. A formal detection and attribution analysis shows that intensification of rainfall events may have been influenced by greenhouse gas forcing of anthropogenic origin. Frequency and magnitude of pluvial floods is on the rise with increasing intense precipitation, while changes of river floods are more complex. High river discharges were found to increase in some regions, but to decrease in other regions, so that no general corollaries can be drawn at the global scale. Heavy rainfall events and pluvial floods are projected to become, almost ubiquitously, more frequent and more intense with progressing climate change, while frequency and magnitude of fluvial floods are likely to increase in many but not all regions.