Simulating Climate Change's Impacts on Typhoons in Taiwan

Heavy rainfall is one of the primary threats to Taiwan as its mountainous terrain makes it susceptible to landslides and river flooding due to mountain run-off. Located in one of the most active regions for tropical cyclones in the North Pacific, the island experiences most of its heavy rainfall events during typhoon season from July through October. The speed and track of the typhoons in relation to the mesoscale mountains of Taiwan help dictate what regions of the island experience the highest rainfall amounts. A typhoon passing to the north of Taiwan will interact with the mountains such that the counties of Taoyuan, Taipei and New Taipei City on the windward side of the mountains would experience the most rain, while Yilan county on the leeward side would experience less. By analyzing past tracks, it has been found that northern track storms such as the previous example tend to produce the most rainfall.

So far in the 21^st century, Taiwan has seen an increase in typhoon related rainfall, having experienced 9 of 12 of the highest hourly rainfall producing typhoons since 2001. It has been hypothesized that climate change is playing a role. The National Science and Technology Center for Disaster Reduction (NCDR) conducted dynamic downscaling HiRAM using 5km WRF simulations to model typhoons impacting Taiwan in the present climate and in a future climate scenario. The present climate simulations run from 1979 to 2015 and consists of four members with prescribed SSTs. The future climate simulations run from 2079 to 2100 using the RCP85 scenario and consists of 16 members with four SST schemes.

To understand climate change’s impact on typhoons in Taiwan, a statistical analysis is conducted on each ensemble member. The simulated storms are sorted into categories, landfalling/non-landfalling and into different track types (north, central, south) depending on where they made landfall or whether they passed north or south of Taiwan. The present and future climate cases can then be compared by category to understand trends in the location of typhoon related heavy rain. Further analysis can be conducted looking into typhoon intensity trends for each track type between climates. From there, extreme cases in both climates can be identified and then compared.