Projections for changes in climatology and extreme events of the Cordex-Australasia domain :|a dynamical downscaling approach

Abstract

Climate change, which is one of the most vital threats to humanity today, will affect many countries on a regional and local scale in terms of common and country-specific areas. In order to adapt to the changing climate, the impacts of climate change in the future should be addressed well. For this reason, joint projects are developed that lead to the production of high resolution climate data in order to accurately determine the impacts of climate change in different parts of the world. In this thesis, within the scope of CORDEX, which is the most prominent of these joint projects today, changes in temperature and precipitation climatology of the Australasia region as well as changes in extreme climate events were examined. For Australasia, one of the least studied regions under the umbrella of CORDEX, the mean air temperature and precipitation changes for three different periods (i.e., 2016 - 2035, 2046 - 2065, 2081 - 2100) were analyzed under three different scenarios (i.e., RCP2.6, RCP4.5, RCP8.5 using global circulation models/global climate models with the approach of multi-model ensemble mean. Later, by using RegCM4.6 regional climate model, low resolution data of HadGEM2-ES and MPI-ESM-MR global climate models were dynamically downscaled to 50 km x 50 km horizontal resolution. Before the future projections were applied in the study, the most suitable Planetary Boundary Layer (PBL) scheme and convective parameterization of the RegCM4.6 model for the region were determined. Accordingly, the RegCM4.6 model was employed using the BATS landuse scheme with the Holtslag PBL scheme and the mixed convective parameterization which is the Tiedtke scheme over lands and the Emanuel scheme over oceans. With RegCM4.6 driven by HadGEM2-ES and MPI-ESM-MR outputs, mean, minimum and maximum temperatures and total precipitation of Australasia have been examined under the RCP4.5 and RCP8.5 scenarios for the periods of 2011-2040, 2041-2070, and 2071-2099 with respect to the reference period of 1971 - 2000. In another part of the study, using the NEX-GDDP dataset with a horizontal resolution of 0.25° x 0.25°, the temperature and precipitation extreme indices for the Australasia region were computed via the RCP4.5 and RCP8.5 scenario outputs of the ACCESS1-0 and MPI-ESM-LR models. While very hot days, tropical nights and heatwaves are used as temperature extremes, very heavy precipitation days, simple daily intensity and consecutive dry days are used for precipitation extremes. The changes in extreme climate events have been analyzed for 2016-2035, 2046-2065, and 2081-2100 with respect to the reference periods of 1981-2000. The results of the analysis show that there will be increasingly higher temperatures in Australasia towards the end of the century. It is concluded that the mean temperature increase expectation of approximately 1.5 - 3 ℃ may be around 5 ℃ at the end of the century and this value can reach up to 7 ℃ for the maximum temperature. It appears that the expected warming may be greater as we approach the end of the century and move from the most optimistic to the most pessimistic scenario. On the other hand, the change in precipitation varies greatly depending on the period and sub-region. Average ±20 % change in precipitation may occur as 50 % or more increases or 30 % or more decreases in some places. In addition to the change in mean temperature and precipitation, it is clear that there will be an increase in temperature and precipitation extremes for the Australasia region. These results indicate that Australasia will have a future in which hot days and nights, heatwaves are more frequent, and the days with heavy precipitation are more common. In conclusion, it is certain that changes in both mean values and extreme climate events pose a very high risk in terms of human health, ecosystems and ecosystem services, habitats and limited agricultural areas in the region.