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Risk of intense precipitation accompanying extreme wet-bulb temperatures

Presentation Date
Friday, December 17, 2021 at 6:15am
Convention Center - Room 206-207



Wet-bulb temperature is an integrated temperature-humidity index of heat stress. Recent work has demonstrated that the annual maximum wet-bulb temperatures in the tropics are capped by a convective instability mechanism and will increase by 1ºC with each 1ºC of the tropical-mean warming (Zhang et al, 2021). A corollary of this finding, which has not been demonstrated before, is that extreme wet-bulb temperatures should lead to atmospheric convection and precipitation. Here we use observed precipitation from the Tropical Rainfall Measuring Mission (TRMM) and wet-bulb temperatures derived from ECWMF reanalysis datasets to demonstrate this corollary. We identify a general pattern for most land regions between 50ºS and 50ºN that precipitation is slightly suppressed the day before TW reaches its annual maximum (TWmax) and is enhanced by around 70% (compared to local summer rainfall) on the day of TWmax and the day after. Precipitation intensities on days of TWmax on average rank the 75th percentile. In particular, about half of the land area between 50ºS and 50ºN has experienced precipitation exceeding the 99th percentile on days of TWmax. We find that the anomalously high convective inhibition (CIN) due to anomalously warm lower troposphere is responsible for the suppression of precipitation preceding TWmax, while the cooling of the lower troposphere following TWmax reduces CIN and enhances precipitation. Our results highlight the increased risk of intense precipitation accompanying and immediately following extreme wet-bulb temperatures, which is consistent with our understanding of atmospheric dynamics.

Zhang, Y., Held, I. & Fueglistaler, S. Projections of tropical heat stress constrained by atmospheric dynamics. Nat. Geosci. 14, 133–137 (2021).

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