Modelling Climate Changes, Biogenic Emissions and Tropospheric Chemistry in Southeast Asia.

Sentian, Justin (2009) Modelling Climate Changes, Biogenic Emissions and Tropospheric Chemistry in Southeast Asia. PhD thesis, Lancaster University.

PDF (11003478.pdf)
11003478.pdf - Published Version
Available under License Creative Commons Attribution-NoDerivs.
Download (50MB)

Abstract

A regional climate model (PRECIS) and a biogenic emission model (BVOCEM) were used to investigate the impact of climate changes on biogenic emissions during northeast monsoon (Dec-Jan-Feb, DJF) and southwest monsoon (Jun-(July)-Aug, JJA) in both the A2 and B2 transient climate scenarios of the IPCC in Southeast Asia. The investigation also explored the regional climate change and biogenic emissions response to future landcover changes, both alone and in combination with atmospheric forcing. Consequently, a tropsopheric chemistry model (CiTTyCAT) was used to investigate the relative impact of climate changes and biogenic emissions on tropospheric chemistry, particularly ozone in both seasons and climate scenarios. A warming across the region occurred, with the largest temperature increase apparent over land areas during DJF and JJA in both the A2 (3.0°C and 3.1°C) and B2 (2.6°C and 2.1°C) climate scenarios. These temperature changes were statistically significant at the 95% level in both climate scenarios across the domain with the exception during DJF (B2 scenario) in some areas over the South China Sea and the Philippines Sea. The increase in solar radiation was also reflected in the increase of surface temperature and decreased cloud fraction in both seasons in the A2 and B2 scenarios. Future changes in other climatic variables, such as precipitation and boundary layer, have shown a high degree of variability. The combined effect of atmospheric forcing and landcover forcing was observed to increase the surface temperature significantly in both climate scenarios. However, the effects of future landcover forcing alone in both seasons in the A2 and B2 climate scenarios were observed to be small and produced cooling temperatures. Projected climate changes in the present-day landcover scenario in both A2 and B2, with the exclusion of the CO2 activity factor, showed an increase in isoprene emissions by 27% (A2) and 13% (B2) in 2100 relative to 2008. In the same scenario, but with the inclusion of future CO2 concentrations of 560 ppm, isoprene emissions were found to be inhibited by 8% (A2) and 19% (B2) respectively. The inhibitory effects of elevated CO2 on isoprene emissions was much larger than that of climate change alone. Meanwhile, the combined effects of climate change and future landcover forcing with the inclusion of the CO2 activity factor accounted for the decrease of future isoprene emissions by 66% (A2) and 60% (B2) respectively. Landcover forcing alone accounted for the decrease of isoprene emissions by 5% (A2) and 6% (B2) with the CO2 activity factor, and conversely the increase of isoprene emissions by 9% (A2) and 5% (B2) without the CO2 activity factor. The CO2 inhibitory effect was more important than the combined effects of climate changes and landcover forcings on isoprene emissions. These results suggest that future emissions of isoprene in the region is largely buffered by a number of competing factors, which is certainly an important consideration when estimating the global isoprene budget. In the present-day landcover scenario, the combined impact of climate changes and biogenic emissions (with the CO2 activity factor) in 2100, surface O3 concentrations in urban (Bangkok) and remote (Danum) areas increased in both climate scenarios. In Bangkok, in the A2 scenario, the surface O3 increased by 16% ((January) and 21% (July); while in the B2 scenario, O3 increased by 15% (January) and 18% (July) respectively. In Danum, in the A2 scenario, the O3 increased by 43% (January) and 28% (July); while in the B2 scenario, O3 increased by 13% (January) and 27% (July). In the future landcover scenario, the combined impact of climate changes and biogenic emissions resulted in a further increase in surface O3 concentrations in both seasons in the A2 and B2 climate scenarios in Danum (between 38% and 77%) and Bangkok (between 12% and 21%). In both locations, biogenic emissions accounted for a larger effect on the increase of surface O3 concentrations in both seasons in the A2 and B2 climate scenarios than that of climate changes. In Bangkok, the combined impact of climate changes and biogenic emissions in the present-day and future landcover scenarios were found to decrease OH concentrations in both seasons in A2 and B2 climate scenarios. The OH suppression was largely due to the oxidation of isoprene by OH radicals. (Abstract shortened by ProQuest.).