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<p>Influenced by the urban heat island (UHI) effect and local topography, an extreme rainfall event occurred in Guangzhou city on May 7, 2017. However, the Tropical Regional Atmospheric Model System (TRAMS) model completely failed to capture this precipitation event, even when the horizontal resolution was increased from 3 km to 500 m. Verification of the forecasts indicated that the TRAMS model’s failure to simulate the local convective initiation process near Guangzhou can be attributed to its overestimated low-level southerly winds. A diagnostic study was conducted to identify the source of this error, using a tendency decomposition approach. The results revealed that the overly simplified land surface scheme and the ignorance of diurnal variations in sea surface temperature resulted in an overestimated sea breeze within the afternoon boundary layer. This overestimated southerly wind then extended to higher levels through vertical diffusion in the boundary layer and persisted into the night, which transported warm and moist airflow northward to the northern Guangdong region and triggered spurious convection. Despite increasing the model’s resolution to a sub-kilometer scale, which mitigate the warm bias of land surface temperatures and the positive bias of southerly winds to some extent, the model still failed to correctly simulate the localized initiation of convective systems near Guangzhou. This study emphasized the importance of refined parameterization in simulating land-sea surface temperature variations for achieving accurate rainfall forecasting in the Pearl River Delta (PRD) region.</p>

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The source of low-level wind forecast error and its influence on simulating the Guangzhou extreme rainfall on 7 May, 2017 using high-resolution TRAMS model

  • 期刊论文

  • 发表日期：

    2025年1月6日

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  • Xiaoxia Lin,
  • Yuntao Jian,
  • Daosheng Xu,
  • Shaojing Zhang,
  • Wenjian Deng,
  • Yerong Feng,
  • Banglin Zhang

摘要

Influenced by the urban heat island (UHI) effect and local topography, an extreme rainfall event occurred in Guangzhou city on May 7, 2017. However, the Tropical Regional Atmospheric Model System (TRAMS) model completely failed to capture this precipitation event, even when the horizontal resolution was increased from 3 km to 500 m. Verification of the forecasts indicated that the TRAMS model’s failure to simulate the local convective initiation process near Guangzhou can be attributed to its overestimated low-level southerly winds. A diagnostic study was conducted to identify the source of this error, using a tendency decomposition approach. The results revealed that the overly simplified land surface scheme and the ignorance of diurnal variations in sea surface temperature resulted in an overestimated sea breeze within the afternoon boundary layer. This overestimated southerly wind then extended to higher levels through vertical diffusion in the boundary layer and persisted into the night, which transported warm and moist airflow northward to the northern Guangdong region and triggered spurious convection. Despite increasing the model’s resolution to a sub-kilometer scale, which mitigate the warm bias of land surface temperatures and the positive bias of southerly winds to some extent, the model still failed to correctly simulate the localized initiation of convective systems near Guangzhou. This study emphasized the importance of refined parameterization in simulating land-sea surface temperature variations for achieving accurate rainfall forecasting in the Pearl River Delta (PRD) region.