Simultaneous characterization of mesoscale and convective‐scale tropical rainfall extremes and their dynamical and thermodynamic modes of change

Abstract

The Superparameterized Community Atmosphere Model (SPCAM) is used to identify the dynamical and organizational properties of tropical extreme rainfall events on two scales. We compare the mesoscales resolved by General Circulation Models (GCMs) and the convective scales resolved by Cloud‐Resolving Models (CRMs) to reassess and extend on previous results from GCMs and CRMs in radiative‐convective equilibrium. We first show that the improved representation of subgridscale dynamics in SPCAM allows for a close agreement with the 7%/K Clausius‐Clapeyron rate of increase in mesoscale extremes rainfall rates. Three contributions to changes in extremes are quantified and appear consistent in sign and relative magnitude with previous results. On mesoscales, the thermodynamic contribution (5.8%/K) and the contribution from mass flux increases (2%/K) enhance precipitation rates, while the upward displacement of the mass flux profile (‐1.1%/K) offsets this increase. Convective‐scale extremes behave similarly except that changes in mass flux are negligible due to a balance between greater numbers of strong updrafts and downdrafts and lesser numbers of weak updrafts. Extremes defined on these two scales behave as two independent sets of rainfall events, with different dynamics, geometries, and responses to climate change. In particular, dynamic changes in mesoscale extremes appear primarily sensitive to changes in the large‐scale mass flux, while the intensity of convective‐scale extremes is not. In particular, the increases in mesoscale mass flux directly contribute to the intensification of mesoscale extreme rain, but do not seem to affect the increase in convective‐scale rainfall intensities. These results motivate the need for better understanding the role of the large‐scale forcing on the formation and intensification of heavy convective rainfall.

Prognostic Power of Extreme Rainfall Scaling Formulas Across Space and Time Scales

“…Additional condensation may occur if destabilization by the large‐scale flow pushes the system toward a different level of convective organization that makes the local environment ever so drier, thereby leading to ∂ t W ≪ 0 and invalidating the scaling approximation. In the case of SPCAM, individual CRMs often show an internally organized structure: Figure S9 shows that 70% of the local CRM rainfall is contained in one single subgrid‐scale rain event at locations of hourly extremes, and according to Figure in Fildier et al () the subgrid‐scale rainy columns span about a third of the domain at locations of GCM‐scale daily extremes. The internal structure of these extremes suggests that efficient suppression of condensation by detrainment of cloudy air is quite unlikely to occur.…”

“…Because both scaling expressions are often used to quantify contributions to changes in extreme rainfall with climate change, we can use results from the previous section to assess the ability of these formulas to characterize increases in the strength of individual extreme events. We will focus on the FT scaling in this section because it better approximates extreme rainfall intensities (section ) and allows for a more complete decomposition into dynamic and thermodynamic contributions (Fildier et al, ).…”

“…It allows one to quantify the contributions to the increase in extreme rainfall by perturbing ω Q and independently (Muller et al, ; O'Gorman & Schneider, ; Romps, ). In particular, the FT scaling is more comprehensive and exhibits three distinct modes of change (Fildier et al, ). It has been used in a wide range of studies, including regional extremes (Sugiyama et al, ), with convective entrainment (Loriaux et al, ), for orographic precipitation extremes (Shi et al, ), and for changes in regional precipitation extremes (Pfahl et al, ).…”

Precipitation Probability and Its Future Changes From a Global Cloud‐Resolving Model and CMIP6 Simulations

“…Trenberth et al () first argued that heavy precipitation intensity should increase due to the increasing atmospheric moisture at the rate of ~7%/K and there must be a decrease in light‐moderate precipitation and/or a decrease of total precipitation frequency. Fildier et al () showed that the extreme precipitation intensity increases by ~7%/K using the Community Atmosphere Model with superparameterization. Intensified heavy precipitation have been observed across many regions of the world (Alexander, ; Donat et al, ; Fischer & Knutti, ; Karl et al, ; Kunkel & Frankson, ; Westra et al, ), especially in the humid regions (Donat et al, ).…”

Contributions of Dynamic and Thermodynamic Scaling in Subdaily Precipitation Extremes in India

“…Understanding the changes in PE in urban areas with warming climate can be valuable in mitigating the adverse social and financial consequences (Fildier et al, ). Since PE occur when air is close to saturation, the Clausius‐Clapeyron (C‐C) relationship is used to explain an increase in the observed and projected extreme precipitation with the rise in air temperature (Ali & Mishra, ; Lenderink & Van Meijgaard, ; Mishra, Smoliak, et al, ; Wasko & Sharma, ; Wasko et al, , ; Westra et al, ).…”