Data fields of topography (elevation, surface slope and aspect), land use and land cover, soil texture, groundwater storage time and various river characteristics are required as input data for the description of the landsurce PROMET (see Table 4.1 and section 3.1). For topographic properties, the generally available digital elevation model of the Shuttle Radar Topography Mission SRTM (JARVIS ET AL.2006) was applied in the Lhasa River basin. The model was up-scaled step-by-step from a resolution of 90 x 90 m up to 1 x 1 km per grid cell using the bilinear interpolation method. Slope and aspect were deduced from the digital elevation model using the terrain analysis tool TOPAZ (GARBRECHT AND
MARTZ 1999), which was also applied in the hydrological catchment analysis. Alongside
the watershed of the catchment and the sub-catchments (see Figure 2.5), the main channel network with the channel slope and the flow direction are the main outcomes of TOPAZ. They, in turn, are required to run the river routing component of PROMET (section 3.1.5). Channel width is also needed. It was derived under the assumption that it correlates with the accumulated upstream area, also provided by TOPAZ, consistent with MAUSER AND BACH (2009). To determine the flow velocity, Manning’s roughness
parameter is needed. For the Lhasa River basin it was deduced by fieldwork during a field campaign in Tibet in September 2006 according to the methods of BARNES (1967). For the simulation of groundwater flows, the distance to the main river channel is required, which is also provided by TOPAZ. Depending on the distance, the storage time constant is set as described in section 3.1.4.
Figure 4.1: Distribution of parameterized land use and land cover classes in the Lhasa River basin, modified according to the NASA TERRA/MODIS land cover product (BOSTON UNIVERSITY 2004).
The NASA TERRA/MODIS land cover product (BOSTON UNIVERSITY 2004) provides
information about land cover and land use in the Lhasa River catchment (Figure 2.9). The classification was modified by intersecting it with the Chinese Glacier Inventory (WDC 2009) to obtain a consistent data set. All grid cells which are partly glacierized were predisposed to rock. Since several classes cover less than one percent of the basin, similar categories were merged for the parameterization. Needleleaf forests and mixed forests were aggregated to the coniferous forest class and amount to 0.5 percent of the basin area, whereas broadleaf forests, woody savannas and closed shrubland were grouped into deciduous forests, which together cover 2.4 percent of the area. Moreover, all cropland classes, which only cover 1.6 percent of the catchment, were summarized as spring barley, which is widely cultivated in Tibet (see section 2.5). While open shrublands, savannas and grassland are used for grazing throughout the whole catchment, these classes are coexistent at a spatial resolution of 1 x 1 km. Furthermore, they have similar characteristics according to field data. They are therefore grouped under grass- and shrublands in this study. Figure 4.1 shows the distribution of the aggregated classes in the Lhasa River catchment.
In order to simulate water transport in plants as well as the energy and mass balances of the land use classes in considering their different properties (see section 3.1.2), the parameters listed in Table 4.3 are required. Within the basin, the classes are uniformly parameterized under the assumption that the properties of the different classes are similar throughout the whole catchment.
Table 4.3: Required parameters for description of the land surface (MAUSER AND BACH 2009).
Parameter Unit
Minimal stomatal conductance m/s
Slope of stomatal conductance with irradiance -
Cardinal temperatures K
Slope of inhibition of stomatal resistance with air humidity - Slope and threshold of stomatal inhibition with soil suction MPa
Root depth m
Daily leaf area index m²/m²
Daily plant height m
Daily albedo %
The parameterization for the non-vegetated classes of rock, residential areas, glaciers and water, as well as for the small percentage of forests, was adopted from the classifications applied in Europe in a variety of studies. Further details can be found in MAUSER AND BACH (2009),HANK (2008)andMAUSER AND SCHÄDLICH (1998).According to literature and data from the field survey 2006, the parameterization of spring barley was adapted to the conditions of Tibet. There, it is grown in April and harvested from August to September (TASHI 2005). The maximum plant height in the model was set to 0.8 m. The course of the daily albedo and the daily leaf area index were adapted, taking measured plant densities into account. The grass- and shrubland which accounts for 83 percent of
the basin area, was divided into areas above 5,500 m a.s.l. and slopes larger than 40 percent, where less grazing is assumed than in the ranges with smaller slopes or those located below 5,500 m a.s.l. On the basis of the parameterization of natural grassland in Europe, the growing height was reduced. The course of the leaf area index and the albedo were modified accordingly. In doing this, the grazing and the lower plant density were considered. The plants are assumed to grow slightly taller in the higher and steeper regions because of missing grazing, although their growth is limited by the altitude and the soil formation under natural conditions. Pictures of the investigation area in Appendix 2 give an impression of the land use.
In order to model the water processes in the soil, the soil component of PROMET (see section 3.1.3) needs soil texture classes, which were taken from the Harmonized World Soil Database (FAO ET AL. 2009, see section 2.4 and Figure 2.6). The required parameters for the classes, listed in Table 4.4, were adapted from the parameterization according to MAUSER AND BACH (2009) and MUERTH (2008).Since the mountainous relief
characterizes the Lhasa River catchment and the soil depth as observed in the field, the soil depth was modified due to elevation and slope. For grid cells above 5,000 m a.s.l. and slopes steeper than 20 percent, a total depth of 0.9 m was assumed, whereas for slopes steeper than 30 percent it was reduced to 0.5 m. In all other cases, it was set to 1.5 m. In differentiating the depth, the slower soil formation processes in higher regions due to climate, topography and broken bedrocks is also considered.
Table 4.4: Required parameters for soil texture parameterization (MAUSER AND BACH 2009).
Parameter Unit
Thickness per soil layer m
Pore size distribution index per layer
Saturated conductivity per layer m/s
Effective pore volume fraction per layer %
Bubbling pressure head MPa
Depth of groundwater table m
With these input data, the hydrological model PROMET can be run. In order to simulate the glaciers with SURGES, subscale glacier characteristics are required. Their derivation is explained in detail in the following chapter. Firstly, the data basis is synthesized. Secondly, the processing of the data is explained.