Aerosol-Induced Intensification of Temperature Maxima during a Mega Heatwave Event in India
Arushi Sharma, CHANDRA VENKATARAMAN, Arpita Mondal, Manish Dhasmana, Dewashish Tiwari, Indian Institute of Technology Bombay
Abstract Number: 34
Working Group: Carbonaceous Aerosols
Abstract
Despite global temperature effects of aerosols being governed by their light absorbing (warming, e.g. black carbon or BC) or scattering (cooling, e.g. sulfate) nature, increases in regional aerosol concentrations are widely believed to cool local, near-surface temperatures. Epidemiological studies suggest an exponential increase in heat-related mortality for the most extreme temperatures, making it crucial to estimate whether aerosol radiative feedback can intensify or weaken temperature maxima during heatwaves. The 2015 mega heatwave event in South Asia claimed 2000 lives in India and 1500 lives in Pakistan.
Here we evaluate aerosol influence on both dry and moist heat stress during the event, using simulations with the chemical transport model (WRF-Chem using RADM2-SORGAM chemistry and MADE microphysical schemes), deploying emissions from a regional emission inventory. Dry heat stress was quantified as the daily maximum dry bulb temperature (Tmax), while moist heat stress as the daily maximum wet bulb temperature (WBT). The difference between a pair of WRF-Chem simulations with (i) both aerosol direct and indirect radiative effects switched on (BASE) and (ii) the aerosol radiation interaction switched off (NoARI), was exploited in the work.
The heatwave period was evaluated to reveal two distinct aerosol-induced effects, both of which led to an intensification or warming of extreme temperatures, thus exacerbating heat stress. During May 22nd-Jun 7th, 2015, aerosols induced an enhancement of dry heat stress (ΔTmax~0.5-2°K; averaged over 15°N-27.5°N; 71°E-85°E), driven by enhanced black carbon concentrations (ΔBC~0.5-1.5 μg m-3). Following this, during Jun 8th-30th, 2015, an increase in moist heat stress (ΔWBT~0.5-2°K), was driven by enhancements in daily relative humidity (ΔRH~1-10%). The paper will discuss the underlying mechanism, which includes absorbing-aerosol induced atmospheric stabilization, leading both to changes in surface energy fluxes and a confinement of moisture in the surface layer, worsening heatwave intensity.