Abstract
Precipitation extremes will increase in a warming climate, but the response of flood magnitudes to heavier precipitation events is less clear. Historically, there is little evidence for systematic increases in flood magnitude despite observed increases in precipitation extremes. Here we investigate how flood magnitudes change in response to warming, using a large initial-condition ensemble of simulations with a single climate model, coupled to a hydrological model. The model chain was applied to historical (1961–2000) and warmer future (2060–2099) climate conditions for 78 watersheds in hydrological Bavaria, a region comprising the headwater catchments of the Inn, Danube and Main River, thus representing an area of expressed hydrological heterogeneity. For the majority of the catchments, we identify a ‘return interval threshold’ in the relationship between precipitation and flood increases: at return intervals above this threshold, further increases in extreme precipitation frequency and magnitude clearly yield increased flood magnitudes; below the threshold, flood magnitude is modulated by land surface processes. We suggest that this threshold behaviour can reconcile climatological and hydrological perspectives on changing flood risk in a warming climate.
Highlights
Precipitation extremes will increase in a warming climate, but the response of flood magnitudes to heavier precipitation events is less clear
We seek to reconcile the extreme precipitation-flood paradox in a warming climate: is there a precipitation threshold beyond which increasing precipitation extremes directly translate into increasing flood risk? We hypothesize that such a threshold should exist because moderately extreme events may be buffered by decreased soil moisture while very extreme events may quickly lead to soil saturation and subsequently to direct translation of precipitation to runoff
We first seek to assess whether there exists a return interval threshold beyond which precipitation (P) increases consistently translate into streamflow (Q) increases, and thereby to increases in flood magnitude
Summary
Precipitation extremes will increase in a warming climate, but the response of flood magnitudes to heavier precipitation events is less clear. For the majority of the catchments, we identify a ‘return interval threshold’ in the relationship between precipitation and flood increases: at return intervals above this threshold, further increases in extreme precipitation frequency and magnitude clearly yield increased flood magnitudes; below the threshold, flood magnitude is modulated by land surface processes We suggest that this threshold behaviour can reconcile climatological and hydrological perspectives on changing flood risk in a warming climate. We find that there does exist a catchmentspecific extremeness threshold (i.e. return interval threshold) above which precipitation increases clearly yield increased flood magnitudes, and below which flood magnitude is strongly modulated by land surface processes such as soil moisture availability This finding may help reconcile seemingly conflicting climatological and hydrological perspectives on changing flood risk in a warming climate. Addressing the precipitation-flood paradox is not possible using observations alone, as the high-end extreme events of interest are rare to nonexistent in temporally limited observational records
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