Atmospheric Aerosol Effects on Regional Precipitation Patterns in Industrialized Regions

Abstract

Anthropogenic aerosol emissions from industry, transportation and residential combustion remain one of the largest
sources of uncertainty in regional precipitation projections, because aerosols alter cloud microphysics through
competing pathways that can either suppress or invigorate rainfall depending on cloud type, background humidity
and pollution loading. We analysed eighteen years (2005-2022) of co-located satellite aerosol optical depth (AOD)
retrievals, cloud microphysical products and surface precipitation gauge records across three heavily industrialized
East Asian basins, the North China Plain, the Sichuan Basin and the Yangtze River Delta, together with a matched
set of five downwind rural reference sites, to quantify how aerosol loading reshapes the frequency and intensity
distribution of regional precipitation. Warm-season shallow and moderately deep convective clouds sampled under
the highest AOD quintile (AOD greater than 0.80 at 550 nm) showed a 31% reduction in light-rain frequency (below
5 mm per day) relative to the lowest quintile, alongside a 14% increase in cloud droplet number concentration and a
2.3 micrometre decrease in cloud-top effective radius, consistent with classical Twomey-type suppression of
warm-rain formation. In contrast, deep convective systems embedded in the same polluted environments exhibited
a 19% increase in the frequency of heavy-rain days (above 50 mm per day) and a systematic upward shift in
radar-estimated echo-top height of 850 m on average, indicating aerosol-driven invigoration through enhanced
latent heat release from delayed freezing of supercooled droplets. The two effects did not offset one another
spatially: suppression dominated the immediate urban and peri-urban core, while invigoration and downwind rainfall
enhancement were concentrated 40-120 km further along the prevailing summer monsoon flow, producing a
measurable redistribution of the seasonal rainfall total rather than a simple net increase or decrease. Trend analysis
over the study period showed a 12% decline in regional AOD following the tightening of national air-quality
standards after 2013, accompanied by a partial reconvergence of light-rain frequency toward rural reference levels,
though heavy-rain frequency remained elevated. These results indicate that aerosol-precipitation interactions in
industrialized regions operate as a spatially structured redistribution of rainfall rather than a uniform suppression or
enhancement, with direct implications for water resource planning and flood risk assessment downwind of major
pollution sources.