Regional Scale Analysis of Extremes in an SRM Geoengineering Simulation

Abstract:

Only a few studies in the past have investigated the statistics of extreme events under geoengineering. In this study, a global climate model is used to investigate the impact of solar radiation management on extreme precipitation events on regional scale. Solar constant was reduced by 2.25% to counteract the global mean surface temperature change caused by a doubling of CO₂ (2XCO2) from its preindustrial control value. Using daily precipitation rates, extreme events are defined as those which exceed 99.9^th percentile precipitation threshold. Extremes are substantially reduced in geoengineering simulation: the magnitude of change is much smaller than those that occur in a simulation with doubled CO₂. Regional analysis over 22 Giorgi land regions is also performed. Doubling of CO₂ leads to an increase in intensity of extreme (99.9^th percentile) precipitation by 17.7% on global-mean basis with maximum increase in intensity over South Asian region by 37%. In the geoengineering simulation, there is a global-mean reduction in intensity of 3.8%, with a maximum reduction over Tropical Ocean by 8.9%. Further, we find that the doubled CO₂ simulation shows an increase in the frequency of extremes (>50 mm/day) by 50-200% with a global mean increase of 80%. In contrast, in geo-engineering climate there is a decrease in frequency of extreme events by 20% globally with a larger decrease over Tropical Ocean by 30%. In both the climate states (2XCO2 and geo-engineering) change in “extremes” is always greater than change in “means” over large domains. We conclude that changes in precipitation extremes are larger in 2XCO2 scenario compared to preindustrial climate while extremes decline slightly in the geoengineered climate. We are also investigating the changes in extreme statistics for daily maximum and minimum temperature, evapotranspiration and vegetation productivity. Results will be presented at the meeting.