Impact of Stratospheric Aerosol Geoengineering on extreme precipitation and temperature indices in West Africa using GLENS simulations

This study assesses changes in extremes precipitation and temperature in West Africa under a high greenhouse gas scenario, that is, a representative concentration pathway 8.5, and under a scenario of stratospheric aerosol geoengineering (SAG) deployment using the NCAR Community Earth System Model version 1. We use results from the Geoengineering Large Ensemble simulations (GLENS), where SAG is deployed to keep global surface temperatures at present day values. This impact study evaluates changes in some of the extreme climate indices recommended by the Expert Team Monitoring on Climate Change Detection and Indices. The results indicate that SAG would effectively keep surface temperatures at present day-conditions across a range of indices compared to the control (CRTL) period, including Cold days, Cold nights and Cold Spell Duration Indicator which show no significant increase compared to the CRTL period. Regarding the extremes precipitation, GLENS shows mostly a statistically significant increase in annual precipitation and statistically significant decrease in the number of heavy and very heavy precipitation events relative to the CRTL period in some regions of Gulf of Guinea. In the Sahel, we notice a mix of statistically significant increase and decrease in Max 1-day and Max 5-days precipitation amount relative to the CRTL period at the end of the 21st century when large amounts of SAG has been applied. The changes in extreme precipitation indices are linked to changes in Atlantic Multidecadal Oscillation, NINO3.4 and Indian Ocean Dipole and these changes in extreme precipitation are driven by change in near surface specific humidty and atmospheric circulation.