The upper tropospheric-lower stratospheric ozone drives summer precipitation and wildfire changes in West Siberia.

Siberian wildfires are pivotal in determining the carbon cycle and climate dynamics, exerting a profound impact on the ecosystems of the entire Arctic region. Over the past few decades, variations in summer precipitation in West Siberia have significantly influenced wildfire activity. This study analyzed precipitation trends in West Siberia from 1982 to 2021 using observations and transient simulations, uncovering a strong correlation between precipitation variability and ozone concentrations in the upper troposphere-lower stratosphere (UTLS). Heightened UTLS ozone levels warm the upper atmosphere over West Siberia during summer. This warming modifies the regional polar jet stream, intensifying its southern branch and weakening the northern one, leading to a southward shift in the jet stream. Consequently, cyclonic circulation anomalies emerge in the upper troposphere, characterized by a barotropic structure with unusual upward movements around 60°N. This upward motion triggers corresponding anomalies in zonal winds in the lower troposphere, fostering a low-pressure system at the surface. This atmospheric shift results in an influx of warm, moist air from the south and cold, dry air from the north into Siberia, enhancing cloud formation and precipitation. Notably, our analysis suggests that the rise in summer precipitation in West Siberia between 1993 and 2010 is linked to increased UTLS ozone concentrations during this period. Conversely, the decline in UTLS ozone since 2010 may increase the risk of wildfires by suppressing precipitation. Our findings underscore the pivotal role of stratospheric chemistry in shaping the regional climate and wildfire behavior.