Our aim is to estimate the timing of ‘peak water’ in the Syr Darya river under a range of future climate change scenarios. Studies to date have focused on smaller sub catchments and tributaries due to the complexity of modelling snow, glacier and hydrological processes across very large catchments. The size of the Syr Darya catchment is 402,760 km² which poses a modelling challenge. We use the Dynamic ﬂuxEs and ConnectIvity for Predictions of HydRology (DECIPHeR) model for this task. DECIPHeR uses a sub-nested catchment approach which means the model can be applied across very large catchments but is still computationally efficient allowing model uncertainty to be explored. To include snow and glacier melt contributions to river flow, we added a degree day snow and glacier melt model to DECIPHeR. The model is currently being calibrated and evaluated using historical river flow observations in the Naryn River catchment, an upstream tributary of the Syr Darya river.
To estimate future river flow, the model will be run using an ensemble of high-end climate change scenarios, defined as climate change that exceeds 2 ∘C global average warming, relative to the pre-industrial period. The ensemble consists of 13 sets of CMIP5 models that have been downscaled using HadGEM3-A and EC-EARTH GCMs and generated by the High-End cLimate Impacts and eXtremes (HELIX) project.