Role of Historical Warming on the Extreme Flooding Event Due to Typhoon Vamco (Ulysses) 2020 in the Philippines.

In November 2020, Typhoon (TY) Vamco (locally named Ulysses) made landfall on the main island of Luzon, the Philippines. It brought intense rainfall resulting in widespread flooding making it the 7th costliest TY in the Philippines. Its thermodynamic characteristic from radiosonde observations during its closest passage shows that while the convective available potential energy (CAPE) was not abnormally high, the saturated layer from 850-600 hPa height had lapse rates slightly larger than the moist-adiabat. Also, high precipitable water of up to 70.3 mm and high relative humidity (RH) from the surface to 400 hPa likely explain the heavy rainfall associated with TY Vamco. Global warming has exerted profound effects on weather patterns around the globe. Consequently, the impact of TY Vamco was used as an example of climate change in the local popular media. In this study, we investigated the influence of historical warming on the rainfall characteristics of TY Vamco using the Weather Research and Forecasting model. The pseudo-global warming method was applied using a 40-yr regression of sea surface and air temperature, and RH. We then used the modeled rainfall to simulate the river discharges of two rivers in the northern Philippines that experienced extensive flooding. Results show that SST has a major influence on the intensity of TY Vamco. However, other factors such as orography and changes in mid-tropospheric humidity negate the effects of historical warming, which resulted in comparable rainfall between the past and present simulations. [ABSTRACT FROM AUTHOR]