A 23-Year Nationwide Study Revealing Aerosol-Driven Light Rain Shifts in China's Emission Control Era

Abstract. Precipitation dynamics critically regulate Earth's hydrological cycle and climate system, yet the mechanisms driving decadal-scale variations in light rain remain poorly quantified. Our analysis of a 23-year (2000–2022) national-scale dataset reveals contrasting trends in light precipitation occurrence: a significant decline (1.0 days yr⁻¹, p < 0.05) during 2000–2013 followed by a pronounced increase (1.9 days yr⁻¹, p < 0.01) in 2013–2022. Cross-temporal analysis demonstrates a national wide inverse correlation (r = -0.55, p < 0.01) between aerosol concentrations and light rain frequency in the China’s Emission Control Era, when the PM2.5 shows an upward trajectory before 2013 followed by a markedly downward decline thereafter, providing a natural experiment to quantify aerosol effects in precipitation. Through multi-algorithm machine learning and causal inference modeling, we further identify aerosol-cloud microphysical processes as the dominant driver, with PM2.5 concentration changes explaining 59–63 % of the decadal trends of light rain. As a result, the PM2.5 reduction (increase) enhances (reduces) light rain frequency by +1.97 (-2.08) days yr⁻¹. Meteorological factors showed negligible temporal variability and thus insignificant explanatory power (<10 % for each individual factor) over a decadal scale. Our findings establish, for the first time, the quantifiable aerosol microphysical effect on light precipitation trends, highlighting dual benefits for China's emission control policies that PM2.5 reduction in 2013–2022 simultaneously enhanced light rain frequency while improving air quality. This work offers critical insights for aligning air pollution mitigation with climate adaptation strategies.