A Modeling Study of the Impact of Topography on Strongly-Forced Afternoon Thunderstorms and Extreme Rainfall in Northern Taiwan: TAHOPE/PRECIP IOP 2

There are many studies which examined the ingredients and physical mechanisms leading to extreme rainfall from weakly-forced afternoon thunderstorms (ATS) over the Taipei Basin. However, the modification of mesoscale processes largely depends on the thermodynamic and kinematic conditions of the environment where convection is embedded. Differences in these environments between weakly and strongly forced ATSs may result in distinct mesoscale features, highlighting the importance of fully understanding the ingredients and physical mechanisms driving extreme rainfall in strongly-forced ATS events over the Taipei Basin.

This study focuses on a strongly-forced ATS event that produced extreme rainfall (~150 mm/3h) over the Snow Mountain Range during the TAHOPE/PRECIP IOP 2 on 31 May 2022, producing flash floods in the rivers of New Taipei City. The observational analysis reveals a “vortex dipole” pattern located over the windward and lee sides within the southwesterly flow. To further examine the impact of topography on this severe ATS event, a series of WRF simulations and terrain-modification experiments were conducted.

The control run reasonably captured the “vortex dipole,” the convection evolution, and the associated rainfall distribution. When the Taiwan terrain was reduced by 50%, the “vortex dipole” weakened, resulting in less intense convection that moved faster to the northeast. A complete removal of the Taiwan terrain caused the “vortex dipole” to disappear, further diminishing convection intensity. These findings emphasize the crucial role of topography in modulating mesoscale processes, highlighting its significant impacts on ATS evolution, rainfall intensity, and the associated weather hazards.