Mega-city development impact on hourly extreme rainfall over the South China Greater Bay Area under near-future climate warming

Hu, Chenxi; Tam, Chi‐Yung; Li, Xinwei; Huang, Kangning; Ren, Chao; Fung, Kwun Yip; Wang, Ziqian

doi:10.1016/j.uclim.2022.101389

Cited by 7 publications

(8 citation statements)

References 62 publications

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“…However, with projected population growth, particularly in the metropolitan region, the conversion of natural land types to croplands and urban areas is expected to continue rapidly (Chen et al, 2020). Additionally, global warming has resulted in a 10% increase in streamflow over the past half‐century in the PRB, and the probability of heavy rainfall is anticipated to rise by 1.3–1.8 times in the coastal urban areas of the GBA (Hu et al, 2023). Consequently, future studies should prioritize mitigating the impacts of land conversions and climate change on flood control.…”

Section: Discussionmentioning

confidence: 99%

Spatiotemporal variability of streamflow in the Pearl River Basin: Controls of land surface processes and atmospheric impacts

Zhang,

Gan,

Yang

2024

Hydrological Processes

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To advance understanding of the spatiotemporal variability of the streamflow in the Pearl River Basin (PRB), we used the Soil and Water Assessment Tool model to simulate the water fluxes from 2010 to 2020 and to identify the underlying controlling mechanisms. The streamflow in the PRB is highly variable and controlled by complex land surface processes and atmospheric impacts over the heterogeneous terrain. Two key factors primarily govern the streamflow: (1) the location of the active precipitation zone, which is determined by the interaction between the monsoon path and uplifting effect of the terrain, and (2) the redistributions resulting from land use and soil characteristics. We observe distinct patterns in the different water fluxes across the different regions. Specifically, surface flow exhibits the highest activity within the precipitation zone. Lateral flow and actual evapotranspiration (AET) have the greatest intensity in the forests and in agricultural regions, respectively, and the aquifer flow is more active in areas with coarse soil textures. The land surface processes of the AET and aquifer retention significantly govern the temporal variability of the streamflow, contributing to the precipitation and streamflow being out of phase in the PRB. Based on the underlying mechanisms driving streamflow variability, we classify the PRB into three substreams: a drought‐prone upstream, a hydrologically active midstream, and a typhoon‐affected downstream, and each substream exhibits distinct spatiotemporal characteristics of streamflow. We find that the time series and probability distributions of the streamflow at different tributaries within each substream are similar. Each probability distribution is multimodal and can be decomposed into three unimodal distributions representing dry, transitional, and wet conditions. Specifically, the PRB features a large and steep dry mode, a flat transitional mode, and a short wet mode.

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Section: Discussionmentioning

confidence: 99%

Spatiotemporal variability of streamflow in the Pearl River Basin: Controls of land surface processes and atmospheric impacts

Zhang,

Gan,

Yang

2024

Hydrological Processes

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“…Each LCZ type is associated with a unique set of UCM parameters and attributes 76 , such as surface albedo, building height, and urban ratio. These parameters were specifically tailored for the GBA mega-city 13 , 32 . Due to the lack of data, we prescribed the same urban land use information for the GBA in 1999 (the historical era) and 2030 (the projected near-future era) 32 .…”

Section: Methodsmentioning

confidence: 99%

Analyzing urban influence on extreme winter precipitation through observations and numerical simulation of two South China case studies

Hu,

Tam,

Yang

et al. 2024

Sci Rep

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This study investigates the impact of urbanization on extreme winter rainfall in the South China Greater Bay Area (GBA) through the analysis of hourly station observations and simulations using the Weather Research and Forecasting Model with the Single Layer Urban Canopy Model (WRF-SLUCM). Data from 2008 to 2017 reveal that urban areas in the GBA experience lower 99th percentile hourly winter rainfall intensity compared to surrounding rural regions. However, urban locations exhibit higher annual maximum hourly rainfall (Rmax) and very extreme rainfall events (99.99th percentile) in winter, suggesting a positive influence of urbanization on extreme winter precipitation. A case study further underscores the role of the Urban Heat Island (UHI) effect in enhancing extreme rainfall intensity and probability in the GBA urban areas. Additionally, two extreme cases were dynamically downscaled using WRF-SLUCM, involving four parallel experiments: replacing urban land use with cropland (Nourban), using historical urban land use data from 1999 (99LS), projecting near-future urban land use for 2030 (30LS), and considering 2030 urban land use without anthropogenic heat (AH) (30LS-AH0). Synoptic analysis demonstrates that cold air intrusion suppresses the GBA UHI in Case 2013 but not in Case 2015. Reduced evaporation and humidity induced by urban surfaces significantly decrease urban precipitation in Case 2013. In contrast, the persistent UHI in Case 2015 enhances local convection and land–ocean circulation, leading to increased moisture flux convergence and amplified urban precipitation intensity and probability in 30LS compared to Nourban. This amplification is primarily attributed to AH, while the change in 99LS remains insignificant. These findings suggest that urban influences on extreme precipitation in the GBA persist during winter, particularly when the UHI effect is maintained.

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“…Dataset-Hong Kong Observatory Tropical Cyclone Best Track data are used to select TC cases and assess model performance (Knapp et al, 2018). Dataset-Variables from WRF model output are available on Zenodo (Hu, 2023).…”

Section: Conflict Of Interestmentioning

confidence: 99%

“…Moreover, as a mega‐city cluster with a powerful annual rainfall amount, numerous studies have investigated the urban influence on extreme rainfall over the GBA. Both observation and numerical modeling results indicated that the UHI effect can significantly enhance non‐TC extreme precipitation in GBA during summer (Fung et al., 2021; Hu et al., 2021, 2023; D. Wang et al., 2015; Wu et al., 2019). However, research specifically focusing on the impact of urbanization on TC rainfall remains limited, further investigation is needed to elucidate the details and mechanisms underlying the urban impact on TC rainfall in the GBA mega‐city.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, as a mega-city cluster with a powerful annual rainfall amount, numerous studies have investigated the urban influence on extreme rainfall over the GBA. Both observation and numerical modeling results indicated that the UHI effect can significantly enhance non-TC extreme precipitation in GBA during summer (Fung et al, 2021;Hu et al, 2021Hu et al, , 2023D. Wang et al, 2015;Wu et al, 2019).…”

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confidence: 96%

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Urbanization Impacts on Tropical Cyclone Rainfall Extremes‐Inferences From Observations and Convection‐Permitting Model Experiments Over South China

Hu,

Tam,

Loi

et al. 2023

JGR Atmospheres

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How urbanization affects tropical cyclone (TC) rainfall is inferred from station observations over the Great Bay Area (GBA, located on the South China coast) and numerical model experiments. Observations from 41 TCs indicate that surface wind is noticeably weaker in urban compared to rural stations during TC passages, while the urban heat island effect is considerably suppressed. Extreme (99th percentile of) hourly rainfall for these TC events during 2008–2017 is more intense over urban compared to rural stations. For eight selected TC cases, dynamical downscaling was carried out using the convection‐resolving Weather Research and Forecasting model, each with three parallel experiments: “Nourban” in which the urban area was replaced by cropland; “AH0” (“AH300”) in which the diurnal maximum anthropogenic heat (AH) was set to 0 (300 W/m2) in city locations. Both AH0 and AH300 show a significant increase in urban hourly rainfall intensity and probability in all ranges (most obvious for heavy rainfall >40 mm/hr), over the GBA mega‐city. Further diagnosis indicates increased moisture flux convergence in urban areas over a 2‐day period during the landfall, contributes to increased rainfall, likely induced by the surface roughness. The influence of AH, however, is found to be insignificant. The increase in accumulated rainfall due to urbanization is proportional to the storm residence time over the city, implying greater rainfall exacerbation for slower or larger TCs. Overall, urbanization intensifies extreme TC rainfall over the coastal GBA mega‐city mainly due to surface frictional convergence, with stronger intensification for storms residing longer over the city.

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Mega-city development impact on hourly extreme rainfall over the South China Greater Bay Area under near-future climate warming

Cited by 7 publications

References 62 publications

Spatiotemporal variability of streamflow in the Pearl River Basin: Controls of land surface processes and atmospheric impacts

Spatiotemporal variability of streamflow in the Pearl River Basin: Controls of land surface processes and atmospheric impacts

Analyzing urban influence on extreme winter precipitation through observations and numerical simulation of two South China case studies

Urbanization Impacts on Tropical Cyclone Rainfall Extremes‐Inferences From Observations and Convection‐Permitting Model Experiments Over South China

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