Variability and Trends of Water Balance Components in Benchmark Catchment Areas of the Tibetan Plateau (WET)
Within the framework of the BMBF's joint R&D project "Tibet and Central Asia: Monsoon Dynamics and Geoecosystems" (CAME), the WET project aimed to develop an integrative model and monitoring system (iMoMoS-WET) that maps the coupling of climate and water cycle with explicit consideration of the process dynamics characterised by relief and land cover in benchmark catchment areas of the Tibet plateau and surrounding high mountain regions. In addition to numerical models, the system also records high-tech monitoring technologies for satellite-based remote sensing of the spatiotemporal distribution of all relevant atmospheric, hydrological and glaciological parameters.
With the selected combination of different scientific and technical methods, it is possible to model water balance components such as precipitation, potential and current evaporation, snow accumulation and melting, glacier melting, runoff and groundwater recharge in selected benchmark catchment areas over a period of a decade in a process oriented and area-differentiated manner using the iMoMoS-WET, and to analyse their variability and trends in order to provide a tool for real-time monitoring and further sensitivity analyses.
In the project WET hydrological systems are considered as benchmark catchment areas, which on the one hand show characteristic structural properties for the Tibetian plateau and surrounding high mountain areas, on the other hand are very well suited to be investigated as models without extensive additional terrain investigations due to already carried out preliminary investigations and the availability of corresponding data. In addition to the Tibet plateau as a whole, the following six study regions were being studied in detail:
- Nam Co
- Purogangri Ice Field
- Southeast Tibet, Linzhi
- Qomolangma, Mt. Everest
- Kailash, Muztagh Ata.
In each region, one to two benchmark catchment areas of different extent and structure were selected, in which glaciers, lakes and rivers as well as wetlands occur. The spatial distribution of the selected sub-regions was based on the ability of iMoMoSWET to investigate the interaction of westerly wind and monsoon circulation and the resulting differences in air mass influences on the water balance components of the WET benchmark catchments.
After successful validation, the iMoMoS-WET was integrated into the infrastructure of the selected research facilities on the Tibet Plateau and the surrounding mountain ranges of the Himalayas and the Pamir Mountains in order to develop these into innovative multifunctional long-term observatories. The operation of the iMoMoS-WET was prepared for the benchmark catchment areas in the sub-regions and the participating regional partners were trained accordingly to enable a real-time continuation of the models and monitoring.
The project "Integrated Model for the Determination of Glacier Mass Balance and Glacier Discharge Donation" (IMOGG) investigated the glacier mass balance in benchmark catchment areas of the Tibetan Plateau on the basis of the energy conversions at the glacier surface. The model scheme couples the atmospheric modules with a subsurface module and enables studies on climate sensitivity and the effects of glacier change on the hydrological system, as well as statements on the effects of monsoon variability and climate change.
The modular design allows the integration of different input parameterization schemes and allows the use of less spatially resolved input data. The approach was based on the integration of existing process understanding regarding melting processes on glaciers. For the radiation module and the turbulence module to solve the energy balance at the glacier surface, proven approaches were taken. The implementation of a subsurface module enables the explicit calculation of percolation and re-freezing of melt water in the snow cover.
In particular, the step away from simple temperature index models to physically based energy balance models in hydrological and climatological modelling was performed for this operational application.
Institute for Tibetan Plateau Research,
Chinese Academy of Sciences