Tropical Cyclone Hazards in a Changing Climate – Results from a New, Columbia Hazard Model

The newly--developed Columbia HAZard model (CHAZ) is used to study changes in tropical cyclone (TC) hazard, the landfall probability and TC wind hazard, due to climate change. CHAZ is a statistical-dynamical model, containing three components representing the complete storm lifetime: a genesis model, a beta-advection track model and an auto-regressive intensity model. All three components depend upon the local environmental conditions, including potential intensity, 850 and 250 hPa steering flow, deep-layer mean vertical shear, low-level vorticity, and midlevel relative humidity. CHAZ, using 400 realizations of a 32-year period (approximately 3000 storms per realization) with environment conditions from ERA-Interim, captures many aspects of TC statistics, such as genesis and track density distribution. Of particular note, it simulates the observed number of rapidly intensifying storms, a challenging issue in tropical cyclone modeling and prediction.

To study TC hazard in a changing climate, CHAZ will be downscaled from global climate models in CMIP5. We focus on two 30-yr periods: current/near-future climate (2006-2036) and future climate (2070-2100) in the Representative Concentration Pathway (RCP) 8.5 scenario. We will look into the individual components in CHAZ to determine whether the changes in the TC hazard between the two climate scenarios is due to the changes in the genesis location, the intensification rate, the track pattern, etc. Analyses will be conducted from a global, basin-wide and regional perspective. We will start by discussing differences in the global and basin-wide TC climatology in these two climates. Then we will use subsets of synthetic storms associated with areas of interest, such as New York City, Miami, and Mumbai, to investigate changes in the regional TC hazard. Changes in the probabilities of the occurrences of high-impact storms will be discussed in the end.