On the Influences of Urbanization on the Extreme Rainfall over Zhengzhou on 20 July 2021: A Convection-Permitting Ensemble Modeling Study

Abstract

This study investigates the influences of urban land cover on the extreme rainfall event over the Zhengzhou city in central China on 20 July 2021 using the Weather Research and Forecasting model at a convection-permitting scale [1-km resolution in the innermost domain (d3)]. Two ensembles of simulation (CTRL, NURB), each consisting of 11 members with a multi-layer urban canopy model and various combinations of physics schemes, were conducted using different land cover scenarios: (i) the real urban land cover, (ii) all cities in d3 being replaced with natural land cover. The results suggest that CTRL reasonably reproduces the spatiotemporal evolution of rainstorms and the 24-h rainfall accumulation over the key region, although the maximum hourly rainfall is underestimated and displaced to the west or southwest by most members. The ensemble mean 24-h rainfall accumulation over the key region of heavy rainfall is reduced by 13%, and the maximum hourly rainfall simulated by each member is reduced by 15–70 mm in CTRL relative to NURB. The reduction in the simulated rainfall by urbanization is closely associated with numerous cities/towns to the south, southeast, and east of Zhengzhou. Their heating effects jointly lead to formation of anomalous upward motions in and above the planetary boundary layer (PBL), which exaggerates the PBL drying effect due to reduced evapotranspiration and also enhances the wind stilling effect due to increased surface friction in urban areas. As a result, the lateral inflows of moisture and high-θe (equivalent potential temperature) air from south and east to Zhengzhou are reduced.

Effects of Typhoon In‐Fa (2021) and the Western Pacific Subtropical High on an Extreme Heavy Rainfall Event in Central China

“…Our result indicated that the strong low‐level easterly airflow between the WPSH and Typhoon In‐Fa plays an essential role in the HnHRE, which is supported by some recent research (Deng et al., 2022; Luo et al., 2022; Y. Nie & Sun, 2022). Unique from the previous literature, the contribution of the WPSH and In‐Fa to the HnHRE is reasonably and quantitatively evaluated in this study, which pointed out that the HnHRE occurred with the aid of the highly favorable configuration of WPSH and In‐Fa circulations and their cooperation.…”

“…Our result indicated that the strong low-level easterly airflow between the WPSH and Typhoon In-Fa plays an essential role in the HnHRE, which is supported by some recent research (Deng et al, 2022;Luo et al, 2022;Y. Nie & Sun, 2022).…”

Mechanism Analysis of a Wintertime Extreme Persistent Heavy Rainfall Event in Hainan Island

“…For example, on July 19–20, 2016, an extensive extreme rainfall event swept across North China, causing 139 human fatalities, 141,000 house collapses, and 718,000 ha of crops damages over the region, leading to a direct economic loss of 10 billion RMB (Xia & Zhang, 2019). More severely, the “21·7” extreme rainfall in Henan caused devastating floods, with a record‐breaking hourly rainfall rate of 201.9 mm hr −1 , leaving 398 human fatalities and a direct economic loss of 120.06 billion RMB (Luo et al., 2022; Su et al., 2021; Wei et al., 2022; Yin et al., 2022), which has brought unprecedented attention to extreme rainfall events. Early warning and forecasting are always a crucial part of disaster prevention and mitigation.…”

Modeling Urban Impact on Zhengzhou Storm on July 20, 2021

“…Beyond local orographic conditions, it is believed that other factors, such as land use and land cover properties, can also play a role in extreme precipitation event (Pielke Sr et al., 2011). Yet, limited attention has been paid to the potential impacts of local land properties on the record‐breaking “July‐20 event” (Luo et al., 2022).…”

“…Beyond local orographic conditions, it is believed that other factors, such as land use and land cover properties, can also play a role in extreme precipitation event (Pielke Sr et al, 2011). Yet, limited attention has been paid to the potential impacts of local land properties on the record-breaking "July-20 event" (Luo et al, 2022).Drastic land cover conversion has occurred in China in the past 40 years, and urban area expansion was one of the major types of land conversion (Liu et al, 2020). The most spectacular urban expansion was certainly in the low-lying coastal zone (e.g., agglomerations in the region of Beijing-Tianjin-Hebei, in the Yangtze River Delta, and the Pearl River Delta), but central China including Henan province has experienced accelerating urbaniza-…”