Abstract
Disdrometer observations obtained by an OTT Parsivel2 during the 2017 Great Hunan Flood from 1:00 a.m. LST 23 June 2017 to 4:00 a.m. LST 2 July 2017 in Changsha, Hunan Province, southern China, are analyzed to diagnose characteristics of raindrop size distribution (DSD). This event was characterized by a large number of small- to medium-sized raindrops (diameters smaller than 1.5 mm) and the mean median volume diameter (D0) is about 1.04 mm. The median values of rain rate R (1.57 mm h−1), liquid water content W (0.10 g m−3), and radar reflectivity Z (25.7 dBZ) are smaller than that of the 2013 Great Colorado Flood. This event was composed of two intense rainfall periods and a stratiform period, and notable distinctions of rainfall microphysics among the three rainfall episodes are observed. Two intense rainfall periods were characterized by widespread and intense convection rains with a surface reflectivity of 48.8~56.7 dBZ. A maximum diameter of raindrops up to 7.5 mm was observed, as well as high concentrations of small and midsize drops, resulting in large rainfall amounts during the two intense rainfall episodes. The mean radar reflectivity of 22.6 dBZ, total rainfall of 17.85 mm and the maximum raindrop of approximately 4.25 mm were observed during the stratiform rainfall episode. The composite DSD for each rainfall episode peaked at 0.56 mm but higher concentrations of raindrops appeared in the two intense rainfall episodes. The Z-R relationships derived from the disdrometer measurements reflect the unusual characteristics of DSD during the flood. As a result, the standard NEXRAD Z-R relationship (Z = 300R1.4) strongly underestimated hourly rainfall by up to 27.5%. In addition, the empirical relations between rainfall kinetic energy (KE) versus rainfall intensity (R) and mean mass diameter (Dm) are also derived using DSDs to further investigate the impacts of raindrop properties on the rainfall erosivity.
Highlights
Persistent heavy rainfall (PHR) events such as the 2017 Great Hunan Flood are characterized by several observable attributes: high intensity, wide range, long duration, and strong stability [1]
It is necessary to study extreme typical heavy precipitation event like the 2017 Great Hunan Flood from multiple perspectives to improve our understanding of such PHR events
During the 2017 Great Hunan Flood from 22 June to 2 July 2017, detailed data from a Parsivel disdrometer, a ground-based dual S-band Doppler weather radar, located at Changsha site, Hunan province, southern China, and 357 rain gauges scattered in the province, were used to measure the microphysical characteristics of this persistent rainfall
Summary
Persistent heavy rainfall (PHR) events such as the 2017 Great Hunan Flood are characterized by several observable attributes: high intensity, wide range, long duration, and strong stability [1]. During the period of 22 June to 2 July 2017, a large area of heavy rainfall with maximum local amounts approximatively 576 mm fell over Hunan Province and adjacent regions, affecting a total of 4,030,700 people and a direct economic loss of ¥6.014 billion, according to the official report. This heavy a rainstorm, which had not been witnessed in this region for several 4.0/). It is necessary to study extreme typical heavy precipitation event like the 2017 Great Hunan Flood from multiple perspectives to improve our understanding of such PHR events
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