Examining the ENSO-typhoon hypothesis

Abstract

Modern typhoon data and historical documents from Guangdong Province, southern China, are analyzed and found to support the El Nino-Southern Oscillation (ENSO)-typhoon hypo- thesis. The hypothesis states that tropical cyclone formation during an El Nino event shifts eastward, with typhoons tending to recurve north, staying away from China. From the comprehensive but short modern record, typhoon tracks are grouped into 3 distinct clusters based on geographic position at maximum and terminal typhoon intensities. The majority of typhoons originate between 110 and 170° E longitude in the latitude belt between 8 and 25° N. In general, typhoons take 1 of 3 paths away from this genesis region—a westerly path between latitudes (straight moving), a west-northwesterly path (recurving), or a north-oriented path that keeps them out to sea. Straight-moving typhoons are a significant threat to the Philippines, southern China, and Vietnam, whereas recurving typhoons occasionally threaten Japan, Korea, and northern China. The number of straight-moving typhoons, when grouped by year, is found to be significantly positively correlated with the number of landfalls over China south of the Tropic of Cancer. Thus, the abundance of straight-moving typhoons is a good indicator of the typhoon threat to portions of southern China. Moreover, the number of straight- moving typhoons is correlated with the ENSO cycle. A long annual time-series (1600-1909) of typhoon landfall counts from Guangdong, extracted from historical documents together with tree- ring proxy records of the ENSO cycle, provide data that independently support this relationship.