Driving Factors of Heavy Rainfall Causing Flash Floods in the Middle Reaches of the Yellow River: A Case Study in the Wuding River Basin, China

Abstract

In the context of climate change, extreme rainfall events have greatly increased the frequency and risk of flash floods in the Yellow River Basin. In this study, the heavy rainfall and flash flood processes were studied as a system. Taking the driving factors of the heavy rainfall causing the flash floods as the main focus, the key factors of the heavy rainfall causing typical flash flood processes were identified, and the driving mechanism by which the heavy rainfall caused flash floods was revealed. Through comparative analysis of the rainfall related to 13 floods with peak discharges of greater than 2000 m3/s since measurements began at Baijiachuan hydrological station, it was found that different rainfall factors played a major driving role in the different flood factors. The factor that had the largest impact on the peak discharge was the average rainfall intensity; the factor that had the largest impact on the flood volume was the rainfall duration; and the factor that had the largest impact on the sediment volume was the maximum 1 h rainfall. The ecological construction of soil and water conservation projects on the Loess Plateau has had obvious peak-cutting and sediment-reducing effects on the flood processes driven by medium- and low-intensity rainfall events, but for high-intensity flash floods, the flood-reducing and sediment-reducing effects of these projects have been smaller. Therefore, despite the background of continuous ecological improvement on the Loess Plateau, the possibility of floods with large sediment loads occurring in the middle reaches of the Yellow River still exists.

Effects of Extreme Precipitation on Runoff and Sediment Yield in the Middle Reaches of the Yellow River

“…The recent extreme precipitation and flood events observed on the Loess Plateau also basically occurred in the northern and central areas of the study area. For example, an extreme precipitation event occurred in the Wuding River from 25-26 July 2017, in which the maximum daily precipitation exceeded 200 mm and the calculated recurrence interval of the event was within the 500 years range, resulting in the peak flow of 4480 m 3 s −1 and maximum sediment concentration of 873 kg m −3 in the downstream Baijiachuan hydrological station [19,20]. In the context of the obvious increase in extreme precipitation in recent 20 years, the risk of flood disasters and soil erosion in the middle reaches of the Yellow River will further intensify in the future.…”

“…Especially after 2000, a large-scale project of returning farmland to forest and grassland has been underway on the Loess Plateau, resulting in an increase in regional vegetation coverage from 32% in 1999 to 63% in 2018, which effectively intercepts slope runoff and sediment [41]. However, in the case of continuous high-intensity extreme precipitation, some soil and water conservation constructions have the risk of being washed away [19]. It is believed that soil and water conservation measures have a significant effect on peak-cutting and reducing sediment during flood processes driven by medium-and low-intensity rainfall events, but they have a limited effect on reducing flood and sediment during high-intensity storm floods [19].…”

“…Observation and model-predicted results found that the regional extreme precipitation events showed an overall increasing trend in the middle reaches of the Yellow River in the last 60 years [17,18]. The enhanced extreme precipitation in the annual flood season increases the potential risk of flood and soil erosion in the watershed, resulting in large socio-economic losses [19]. At the same time, due to the implementation of large-scale soil and water conservation measures in the Loess Plateau, the runoff and sediment in the main sub-watersheds of the middle Yellow River showed an obvious downward trend, which further changed the relationship between precipitation, runoff, and sediment yield in the area [20,21].…”

Flood vulnerability analysis using the frequency ratio method with the watershed ecosystem in Bulukumba Regency, South Sulawesi Indonesia

“…In addition, the distribution of floods comes from upstream regions with very high rain levels. Increased rainfall is the main factor that triggers flooding [62,63]. Heavy rainfall over a long period trigger flooding in the downstream area, derived from an increase in surface runoff that leads to a rise in the surface of the river flow and an increase in sediment in the downstream area [64][65][66].…”

Measuring Resilience of a Tourism Village Against Flash Flood Disaster

“…Even more, community livestock which consisted of 107 cattle, later perished in the water, and ten cages were said to have suffered damage [2]. As major driving role of flash flood, heavy rainfall intensity and duration are the factors that that had the largest impact on the peak discharge, and flood or sediment volume [3]. According to the Brantas River Basin Center (BBWS), heavy rain was the main factor in the Brantas River's overflow and flushing of Batu City.…”