Large Increasing Trend of Tropical Cyclone Rainfall in Taiwan and the Roles of Terrain and Southwest Monsoon

Abstract

Since the beginning of the 21st century Taiwan has experienced a dramatic increase in typhoonrelated rainfall. Some investigators suggested that they are the manifestation of global warming effects. However, an analysis of typhoon rainfall intensity with respect to typhoon tracks in different landfall phases relative to the Central Mountain Range indicates this is unlikely the cause. Rather, most of the recently observed large increase in typhoon rainfall in the pre-landing and overland phases is the result of slower moving tropical cyclones (TCs) and their tracks relative to the high mountains. A positive feedback mechanism in which the convective heating pattern forced by topography acts to slow down the TC motion, which is most efficient for the slowly-moving northern-track storms. Another factor contributing to increased TC-related rainfall is the interaction between the typhoon circulation and southwest monsoon wind surges. This factor is most important after the typhoon center exits Taiwan and led to the increase of both typhoon rainfall intensity and rainfall amount in the new century. Both the slower TC motion and the increased monsoon interaction are consistent with the recently observed multidecadal trend of intensifying subtropical monsoon and tropical circulations, which is contrary to some theoretical and model projections of global warming. There is also no evidence of a positive feedback between global warming-related water vapor supply and TC intensity in the typhoon rainfall increase, as the number of strong landfalling TCs has decreased significantly since 1960 and the recent heavy rainfall typhoons are all of weak to medium intensity.

An overview of the tropical cyclone database at the Central Weather Bureau of Taiwan

“…It has been suggested that the topographic effect of the Central Mountain Range (CMR) in Taiwan is an important factor influencing the TC-related rainfall (e.g., Chang et al 1993;Kuo et al 2017). In order to provide a more accurate representation of the TC-induced precipitation, the CWB has made a great effort to expand the high altitude stations in recent years, even though it is quite difficult and dangerous to build as well as do the follow-up maintenance.…”

A New Look at Storm Separation Technique in Estimation of Probable Maximum Precipitation in Mountainous Areas

“…The average record length for these stations is 36 years with a range from 20 to 58 years. Besides, six outstanding severe storms in Taiwan all caused by tropical cyclones (TCs) with similarly southwesterly inflow of water vapor [32,[44][45][46][47] have been selected for transposition analysis. Hourly precipitation observations from raingauge stations during the period of the TC were utilized to develop isohyets of duration rainfall maxima for each storm.…”

Sustainable Management of a Mountain Community Vulnerable to Geohazards: A Case Study of Maolin District, Taiwan

“…Warm, moist air produced by typhoon formation causes continuous torrential rain on windward-sloping terrain [5,6]. As a result, heavy rainfall persists even after a typhoon leaves Taiwan [7]. Moreover, typhoons often engage in tremendous changes in motion and structure when approaching or moving across an island [8,9], making their paths difficult to forecast.…”