Work Package 1
Impact of global change processes on the water resources of Central Asia, Mongolia and the Kharaa basin

Scientists and research assistants in work package 1
University of Kassel, Center for Environmental Systems Research: L. Menzel and J. Priess (project leaders), T. aus der Beek, C. Schweitzer and F. Wimmer (PhD students), T. Törnros (research assistant), M. Chimed-Ochir (student)

Aims of the work package
Both for the model region (Kharaa catchment) as well as for Mongolia and Central Asia, the potential impact of global change processes on water resources is assessed. This includes the analysis of potential impacts of changes of population, economic growth, land cover and climate on water use (in different water use sectors) and hydrology (e.g. flow regimes, frequency of extreme run-off events). These tasks are only achievable through close cooperation between Mongolian and German scientists. Therefore, another aim is to intensify and to permanently establish an exchange of expertise and to support capacity building activities.

Current activities and results of work package 1 (WP1):
On the large scale, the global water model WaterGAP has been applied to evaluate the water resources of Mongolia on a 50 x 50 km spatial resolution. Monthly maps of runoff, evapotranspiration, water use and water stress were generated for current climate conditions (period 1971-2000). The maps are available to all project partners. A first assessment of the occurrence of permafrost in Mongolia has also been carried out with WaterGAP. It shows the distribution of discontinuous and continuous permafrost over the country and is in good agreement with existing permafrost maps. These investigations form the base for coming investigations on the impact of permafrost and permafrost thawing on hydrological conditions, with special focus on climate change. A preliminary simulation of IPCC climate scenarios (A1B and B1) with WaterGAP for the period until 2100 results in a decrease of permafrost distribution over Mongolia of 54-69%.

On the scale of the Kharaa river basin, the conceptual hydrological model HBV has been implemented. After the successful calibration of the model, a survey of the water resources and the most important hydrological processes in the Kharaa and its individual subbasins has been carried out for current climate and land-use conditions. Results are daily simulated data on runoff and its individual components, including groundwater recharge, potential and actual evapotranspiration, snow cover and snow water equivalent as well as soil moisture (Fig. 1). The data will serve as input to several work packages of the MoMo-project.

Result from the hydrological simulation with HBV-D for the Kharaa-basin. For the year 1998, the following results are shown (from top to bottom): daily simulated actual evapotranspiration, daily simulated snow water equivalent as well as fractional snow cover (in %) over the catchment, daily simulated soil moisture (in % of field capacity FC) and a comparison between observed and simulated discharge at gauge Darkhan

The highest degree of detail comes from the application of the physically based hydrological model TRAIN, since it includes the representation of major hydrological processes in a most realistic manner. The preparation of first model runs required a spatial interpolation of the available meteorological data on a 1 x 1 km grid lain over the Kharaa catchment. This required the development of an interpolation routine which is based on proven geostatistical methods such as Kriging or Inverse Distance Weighting (IDW). So far, daily interpolated grids of temperature, precipitation, relative humidity, wind speed and net radiation are available for the years 1986-2006. First areal applications of TRAIN over the whole Kharaa basin demonstrate the high spatial detail of this approach, clearly showing the high heterogeneity within the catchment (Fig. 2).

Actual evapotranspiration for the year 2006 simulated with TRAIN. The annual data were deduced from daily gridded data which are available on a 1x1 km resolution over the whole Kharaa catchment

Currently, the available meteorological time series are analysed with regard to the identification of possible trends. For example, a clear trend towards an increasing summer temperature in the Kharaa basin has been identified which strongly increases the (simulated) potential evapotranspiration. This again leads to decreasing soil moisture levels and reduced runoff. These investigations are first steps towards the integration of climate change scenarios in the studies which will be carried out within the next few months.

Cooperation with Mongolian partners
During the MoMo status conference in Mai 2008 in Ulaanbaatar, the cooperation with IMH (Institute for Meteorology and Hydrology, Drs. Davaa and Oyunbaatar) and NAMHEMM (Dr. Enkhtuvshin) was accentuated through discussions and the completion of another cooperation agreement. Furthermore a talk with Dr. Chimed-Ochir from WWF Mongolia served to exchange relevant information and to discuss a possible cooperation.