Periodic extreme rainfall in a warmer climate due to stronger convectively-coupled waves

Abstract

Tropical regions may experience periodic extreme precipitation and suffer from associated periodic deluges in a warmer climate. Recent studies conducted small-domain (around 100 km x 100 km) atmospheric model simulations and found that precipitation transitions from a steady state to a periodic oscillation state in a hothouse climate when the sea surface temperature reaches 320-325 K. Here we conduct global-scale atmospheric model simulations with different complexity, and we find that tropical precipitation in convective regions already transitions to a O(10 day) periodic oscillation state with a O(100 mm/day) amplitude at 305-310 K. This temperature is substantially lower than previously reported, and within reach in a century under a high carbon emission scenario. We attribute the onset of the periodic extreme precipitation to the intensification of convectively-coupled waves, which occurs at temperatures much lower than the radiative mechanism responsible for the transition around 320-325 K identified before.

Figures (13)

• Figure 1: Transition to periodic precipitation in global climate model simulations.a,b, Tropical ($20^\circ$S-$20^\circ$N) precipitation in present climate and a +10 K warmer climate. The results are averages over the last 10 years in 15-year simulations of the atmospheric model GFDL-AM4 (see Materials and Methods). c-f, Regional mean 3-hourly precipitation time series in a selected 50-day period for four regions, in present climate (blue), a +5 K warmer climate (black) and a +10 K warmer climate (red). The results are from day 280 to 330 for Central Africa ($3^\circ$S-$3^\circ$N, $26^\circ$E-$32^\circ$E), day 53 to 103 for Indonesia ($4^\circ$S-$2^\circ$N, $95^\circ$E-$101^\circ$E), day 132 to 182 for Pacific ($2^\circ$N-$8^\circ$N, $154^\circ$E-$160^\circ$E) and day 113 to 163 for Amazon ($3^\circ$S-$3^\circ$N, $117^\circ$W-$123^\circ$E), all in the last simulation year. g-j, The power spectrums of the 3-hourly precipitation time series (normalized by the mean precipitation) over the last 10 years in all 15-year simulations based on a bootstrap method (see Materials and Methods).
• Figure 2: Transition to periodic precipitation in cloud-resolving model simulations.a, 40-day domain-mean precipitation time series in small-domain simulations, with SST ranging from 305 K to 325 K with an increment of +5 K. b, 40-day domain-mean precipitation time series in small-domain simulations coupled to gravity waves, with SST ranging from 290 K to 310 K with an increment of +5 K. c, 40-day precipitation time series averaged over the top 10% SSTs in 3-D Mock Walker simulations, with the domain-mean SST ranging from 290 K to 310 K with an increment of +5 K.
• Figure 3: The periodic precipitation is due to the self-reinforcement of convectively-coupled waves.a,b, The steady-state (i.e., radiative convective equilibrium) vertical profiles of domain-mean potential temperature $\theta$ and specific humidity $q$ in small-domain cloud-resolving simulations, with SST ranging from 290 K to 310 K with an increment of +5 K. c, A schematic showing how convectively-coupled waves reinforce themselves.
• Figure 4: The precipitation cycles in a warmer climate. The left column shows the 15-day time series of domain-mean variables from the 310 K small-domain cloud-resolving simulation coupled to gravity waves, and the right column shows the time series of the same variables averaged over the selected region in Indonesia from the +10 K global climate model (GCM) simulation. a,e, Precipitation. b,g, The large-scale vertical velocity induced by gravity waves. c,h, Latent heating rate. d,i, Temperature anomaly relative to the steady state. e,j, Specific humidity anomaly relative to the steady state.
• Figure S1: The transition to periodic precipitation in global climate model simulations is not due to large vertical gradient in radiative cooling rate. Results here are the vertical profiles of time-average radiative heating rates in the periods and regions as shown in Figure \ref{['fig:AM4_precip_series']}.