Change in Climate Impact Assessment from CMIP5 to CMIP6 in a High-Mountaineous Catchment of Central Asia

In this study we investigated the impacts of climate change on a large nivo-glacial river basin (Naryn Basin) in Central Asia (Kyrgyzstan) using two different families of General Circulation Models (GCMs). Hence, we use the widely used ISIMIP2 (Inter-Sectoral Impact Model Intercomparison Project) data which is based on the GCMs of the 5th stage of the Coupled Model Intercomparison Project (CMIP5), as well as the newly derived ISIMIP3 data, which uses the latest GCM data from phase 6 of CMIP (CMIP6) to drive a hydrological model (Soil Water Assessment Tool - SWAT). As both sources of forcing (ISIMIP2 & ISIMIP3) show considerable differences in multiple aspects such as used GCM family, projections, bias-adjustment technique and reference dataset, we evaluate and compare the individual projected changes of both generations on different variables of the hydrological cycle, such as snowmelt, evapotranspiration and soil moisture. In order to quantify the uncertainty contribution of different components along the modelling chain we perform a sensitivity analysis using an ANOVA (Analysis of Variance) approach. Hereby, it is intended to reveal which source (CMIP phase, GCMs, scenario) can be attributed the largest contribution. Results show that significant differences in the impact assessment can occur depending on the
CMIP generation. It is also shown that the CMIP phase has a high contribution to the total uncertainty estimates. However, in a next step special ephasize is put on the improvement of nivo-glacial processes, which will be performed by an improvement of the hydrological model SWAT, by integrating a glacier module which accounts for not only for glacier mass balance changes but also considers glacier recession and to a limited degree  potential advance.