The boreal forest area of the Russian Plain is an unique territory being a large area of natural regrowing resources in Eastern Europe, and on the other hand, a source area of numerous large East-European rivers which serve as transport arteries and as sources for drinking water and food. The existence of the these forests and the preservation of their hydrological regime mainly depends on the stability of forest ecosystems with respect to changes on climate conditions and land-use. Therefore the simulation and prediction of present and future hydrological regime play an important role within this study. Among the models newly developed and operated by the GIETH group, the spatially distributed model PREVAH (Precipitation-Runoff-Evapotranspiration- HRU model) was chosen for this study. The application of the PREVAH model in the Volga catchment extends the experience in using this model in lowland catchments with some outstanding typical characteristics, i.e. large amount of lakes and marshland. The studied catchment of the Upper Volga to the gauging station Selishe was selected with respect to its representativity within the whole boreal forest area, to available datasets and to the co-operation with project partners.

    application of the PREVAH catchment model in the Upper Volga catchment and spatially distributed modelling of runoff and other water cycle components in daily steps throughout the period 1993-1996 for the observed present climate conditions
    development of model components that describe processes especially relevant in the Volga Forest area (i.e. water exchange in lakes and marshlands) and estimation of its parameters
    simulation of hydrological processes in the Upper Volga catchment with respect to potential future climate and land-use changes

The Upper Volga catchment area belongs to the central part of the large main watershed region of the Russian Plain. This watershed region includes source basins of the most important rivers of the Eastern Europe. The central watershed region approximately corresponds with the Valdai Hills and has an area about 70000 km^2. It belongs to the Moscow synclinal which is part of the Precambrian Russian Sheet which has been formed by crystalline and sediment rocks with high degree of metamorphosis. Due to the coupling of the geological and geomorphological processes, the recent surface of the area looks like a funnel containing the Upper Volga Lakes in its central depression part.
The catchment up to the runoff gauging station Selishe has an area of about 3700 km². It includes the depression part with the largest Upper Volga Lakes Sterzh, Vsyelug, Pyeno and Volgo and surrounding elevations of the Valdai Hills. The highest point of the studied catchment is 321 m a.sl.
The most frequent soil type is the mixed grass-podsol type covering the Quaternary moraines. Areas under particularly humid conditions are covered by marshy soils, especially in large depressions without distinct near surface runoff. The whole catchment area is far-reaching forested with some parts of meadows. The mostly present forest type is the coniferous- mixed forest which is primarily composed by fir trees and birch trees. Leafy forests are frequently present as well; they mainly consist of birch, alder, aspen and willow trees, accompanied on the ground by grass and berries. Marshy vegetation is composed of berries with grass and some pine trees. Meadows with several grass types are partly used as pastures and are frequently located along the lakes.

The input datasets that are necessary for the spatially distributed modelling of water balance and hydrological processes are twofold: first, the spatial physiographic data, and second, the meteorological and hydrological data.

The physiographic data include the topography, land use, soil type and geology and were prepared in a grid with 500x500 m cell size. The realisation of a digital elevation model (DEM) by digitalisation and interpolation occurred using the GIS ARCInfo and a geographical map. The other layers were separately digitised from a series of thematic paper maps of the catchment. With this spatial resolution the approximated extent of the Volga Forest catchment is 14707 cells (3677 km²). The relative homogeneous and flat landscape throughout the basin suggest that the chosen grid resolution may be appropriated to show the spatial differences of the water balance components.
For the management of the digital datasets, the software package HYREUETH (Hydrological Response Unit ETH) was developed. It accelerates the pre-processing of the digital maps and build the HRUs in comparison with the common GIS-Softwares and also includes a complete topographical analysis, the possibility of aggregating the land use classes to hydrologic relevant classes and of assigning the parameterisation of the soil properties from the map of the soil types.

The model uses 6 meteorological input variables: precipitation, air temperature, wind speed, global radiation, vapour pressure and sunshine duration. Within the Upper Volga region, four meteorological stations of the Russian Meteorological Service are operated: Ostashkow, Toropetz, Kakowkino and Zapowednyi. The first two stations are located outside of the selected catchment, but they allow to interpolate the data over the axis West-East throughout the catchment. The spatial interpolation of the data from these stations will result in the distribution of the meteorological input variables within the Upper Volga catchment on the raster structure 500x500 m.

The hydrological model PREVAH (Precipitation-Runoff-Evapotranspiration-HRU model) uses spatially distributed parameters that are based as far as possible on physical principles. It consists of several subsystems such as a snow model, an interception model, a model of soil water storage and depletion by evapotranspiration, a runoff generation model and a discharge concentration and a flood-routing model. The parameterisation for each HRU is based on information derived from the DEM (flow direction, flowpaths, elevation, exposure, slope, shading), from soil maps (plant-available soil fieldcapacity, soil depth, soil conductivity) and from the landuse map. For the determination of evapotranspiration, additional parameter values are introduced. They have been partly estimated from investigations in test areas and by part from experience. The most important parameters which vary in time (monthly) are: albedo, root depth, interception storage capacity, vegetation height, leaf area index (LAI) and minimum stomatal resistance of the various classes of vegetation.

Calculations of the climate scenarios for the Upper Volga Area were performed using the ECHAM 4 GCM (General Circulation Model). It was developed at the Max-Planck Institute for Meteorology in Hamburg and provides world-wide high resulted simulations of present and future climate in a raster field corresponding to 1.1° x 1.1° grid spacing. An integration over 10 years of the ECHAM 4 within the selected Upper Volga area has been carried out for present climate conditions ('control run') was taken as a basis for comparisons with experiments for predicted conditions (doubled air carbon dioxide content - 'scenario run'). The results suggest that the year total amount of precipitation should increase by about 11% (from 700 to 780 mm) with a considerable increase for April (this could be a very positive feedback for the groundwater recharge at the begin of the growing season). The mean increase of the air temperature is about +2.9°C (maximum of +4.7°C for December and minimum of +1.7°C for July).

During the second project year (October 1999-October 2000), the main modelling work of the Upper Volga catchment at the profile Selishe will be carried out. It will include the following steps: