Projected Changes in Climate Extremes Using a High-Resolution Regional Climate Model over Türkiye

Projections of changes in climate extremes are important in evaluating the potential impacts of climate change on the environmental and natural systems. The objective of this study is to assess the changes in the extreme climate indices over Türkiye. The future projections of a subset of extreme climate indices derived from a regional climate model driven by the outputs of three CMIP5 Earth System Models (ESM) under two Representative Concentration Pathway (RCP) scenarios are analyzed. In this chapter, the performance of the regional climate model is examined, RegCM forced by three of the CMIP5 ESMs, HadGEM2-ES2-ES, MPI-ESM-MR, and CNRM-CM5.1, in simulating nine indices of extreme events in Türkiye. ESM simulations are downscaled to the first 50 km coarse resolution over Med-CORDEX domain and then 10 km high-resolution over Türkiye using the regional climate model, RegCM4.3. The simulations cover the periods of 1970–2000 for reference and 2015–2100 for the future with proposed changes under Representative Concentration Pathways 4.5 (RCP4.5) and 8.5 (RCP8.5). A high-resolution gridded surface climate dataset is of great value for the validation phase of the high-resolution climate models and the daily temperature observations are interpolated to regular grids which coincide with the simulation's grids by using the PRISM (Parameter-elevation Relationships on Independent Slopes Model) approach. High-resolution regional climate model performance is evaluated for the reference period by using gridded observations for extremes. Validations of the indices are carried out by comparing the average values from the three downscaling simulations against the observations. From the comparison of mean value and statistical characteristics between observed and simulated indices, it can be seen that the models generally have a good performance in reproducing the extreme indices. The projections are shown in three time slices of 30 years, 2015–2040, 2041–2070, and 2071–2100. The projections show that the increasing rates of extremely hot days (TX35) and summer days (SU25) indices are projected over Türkiye during the third time slice (2071–2100). The increases of these extremes under the RCP8.5 scenario are more pronounced than in RCP4.5 with a significant decrease in frost days for both emission scenarios. Insignificant decreases in heavy (R10) and very heavy rainy days (R25) are projected for the future time slices under both RCP4.5 and RCP8.5 scenarios. Maximum 1-day total precipitation (RX1d) is projected to slightly increase in Türkiye by all models for both RCP4.5 and RCP8.5 scenarios at the end of the projection period. However, simulations showed that the maximum 5-day total precipitation (RX5) is not expected to change much. A significant decrease in dryness measured by the index of consecutive dry days (CDD) over Türkiye was found in all three downscaled ESM results. This leads to more severe droughts being expected in Türkiye, especially through the end of the century.