On the flood peak distributions over China

Abstract

Abstract. Here we for the first time present a nationwide characterization of flood hazards across China. Our analysis is based on an exceptional dataset of 1120 stream gauging stations with continuous records of annual flood peaks for at least 50 years across the entire country. Our results are organized by centering on various aspects of flood peak distributions, including temporal changes in flood series and their spatial variations, the statistical distribution of extreme values, and the properties of storms that lead to annual flood peaks. These aspects altogether contribute to an improved understanding of flood hydrology under a changing environment over China and promote advances in flood science at the global scale. Historical changes in annual flood peaks demonstrate frequent abrupt changes rather than slowly varying trends. The dominance of decreasing annual flood peak magnitudes indicates a weakening tendency of flood hazards over China in recent decades. We model the upper tails of flood peaks based on the generalized extreme value (GEV) distributions. The GEV shape parameter is weakly dependent on drainage area, but it shows spatial splits tied to rainfall climatology between northern and southern China. Landfalling tropical cyclones play an important role in characterizing the upper-tail properties of flood peak distributions especially in northern China and southeastern coast, while the upper tails of flood peaks are dominated by extreme monsoon rainfall in southern China. Severe flood hazards associated with landfalling tropical cyclones are characterized by complex interactions of storm circulations with synoptic environments (i.e., mid-latitude baroclinic disturbances) and regional topography.

Causal effects of dams and land cover changes on flood changes in mainland China

“…This study takes the first step to explain flood changes quantitatively on a national scale in China. In this study, urbanization and dam constructions significantly change annual maximum discharges in the middle and down streams of the Yellow River Basin and the Haihe River Basin, where step changes were detected by Yang et al (2019). As a major human residence with a high density of population, the North Plain of China experiences fast urbanization in recent years (Du et al, 2018), which brings larger flood risks on lives and properties.…”

“…In addition, the degree of dam regulation is larger in northern China because the annual runoff is much smaller than that in wet southern China. In this study, after removing the catchments with nonnegligible impacts of urbanization and dams, the unexplained decreasing trends occur in the middle and down streams of the Yellow River Basin and the upper streams of the Haihe River Basin, where decreasing trends were also derived by Yang et al (2019). Yang et al (2019) interpreted these trends as the results of soil conservation practices (Bai et al, 2016) and decreasing extreme rainfall (Yang et al, 2013;Wu et al, 2016).…”

“…In this study, after removing the catchments with nonnegligible impacts of urbanization and dams, the unexplained decreasing trends occur in the middle and down streams of the Yellow River Basin and the upper streams of the Haihe River Basin, where decreasing trends were also derived by Yang et al (2019). Yang et al (2019) interpreted these trends as the results of soil conservation practices (Bai et al, 2016) and decreasing extreme rainfall (Yang et al, 2013;Wu et al, 2016). Besides, other reasons include decreasing soil moisture (Cheng et al, 2015;Yang et al, 2020a) and the impacts of cascade small soil-retaining dams (Yang et al, 2020b).…”

Causal effects of dams and land cover changes on flood changes in mainland China

“…Yang et al (2019) interpreted these trends as the results of soil conservation practices (Bai et al, 2016) and decreasing extreme rainfall (Yang et al, 2013;Wu et al, 2016). Besides, other reasons include decreasing soil moisture (Cheng et al, 2015;W. C. Yang et al, 2020) and the impacts of small, soil-retaining cascading dams (X. N. .…”

“…However, defining numerous variables to represent confounders may be an endless task. For example, climatic confounders are ambiguous because floods are caused by different climatic factors (e.g., long rainfall, short rainfall, snowmelt, and rain on snow) in different regions (Stein et al, 2020;W. C. Yang et al, 2020;Merz et al, 2020).…”