Drivers and feedbacks impacting the Caspian Sea hydroclimate

The Caspian Sea is the world’s largest land-locked lake. It plays a key role in the Pontocaspian region, with a unique ecosystem providing numerous ecosystem services to millions of people. Large variations in Caspian Sea level have occurred in the past and are projected for the future. However, there is considerable debate about the importance of different drivers and feedbacks leading to these variations. The primary aim of this thesis is to use a modelling approach to improve our understanding of Caspian Sea hydroclimate and sea level from the late Quaternary to the end of the 21st century. Firstly, contributions to Caspian Sea level from glacial-interglacial climate change, topographic changes due to ice-sheet loading, and ice-sheet meltwater were explored by combining climate model simulations and ice-sheet reconstructions to drive a hydrological model. The results show that the reorganization of river drainage systems due to Fennoscandian ice-sheet growth and retreat played the dominant role in the variation of the Caspian Sea level in the late glacial high-stand, while hydroclimate change was the major factor leading to the early Holocene low-stand. Secondly, given that large changes inCaspian Sea area will accompany changes in sea level, a separate climate model experiment examined the extent and magnitude of subsequent climate feedbacks. Results indicate an important local negative lake surface-evaporation feedback and remote teleconnections, impacting as far as the North Pacific. This also demonstrates the need for accurate representation of the Caspian Sea in climate models. Finally, a hydrological balance model was used to explore future Caspian Sea level changes based on multi-model climate projections from the Coupled Model Intercomparison Project (CMIP5 and CMIP6) and idealized water extraction scenarios. The combined impacts of anthropogenic warming and water withdrawals will lead to a decline in Caspian Sea level and the desiccation of the shallow northern Caspian Sea before 2100. This will have multifaceted implications for the surrounding communities, increasing freshwater scarcity, transforming ecosystems, and impacting the climate system