Past global climate conditions and the impact on the Tibetan hydrological cycle

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The major source of variation in landscape and ecosystems in Tibet is the regional branch of the hydrological cycle. In particular, the biosphere suffers from floods and droughts, which are due to short and long-term variability and the temporal shifts within the annual cycle. There is sufficient observational evidence that climate conditions and in particular the hydrological cycle have changed considerably in the past. This project focuses on the simulation of the variability of the hydrological cycle with a global climate model including atmosphere, ocean, land and sea ice, and the biosphere. The variability of the hydrological cycle is analysed on all relevant time scales from months to centuries. Although a regional approach might appear sufficient as a first step, climatological experience shows that, due to the coupling to the global climate system, any regionally restricted view of the hydrological cycle is insufficient. The results of these simulations for extreme global and regional conditions allow a comparison with observational findings in Tibetan tree-ring and lake sediments within the joined project. To assess the long-term climate variability, several climate periods are singled out, which represent extreme long lasting climatic states or are relevant for the analyses of trends and climatic changes.