DatasetsForcing: Daily Precipitation, Tmax, Tmin, and Wind SpeedData source: 158 meteorological gauge stations; Data length :1961.1.1—2009.12.31Vegetation: from UMD global 1km ×1km Land CoverSoil: from IGBP-DIS[2000] (International Geosphere—Biosphere Programme Data and Information System ) , Resolution: 1/12° ×1/12°All forcing data were interpolated to 1/12° ×1/12° grid.Observed streamflow data:

11 Abstract

66 Summary and Further work

The Tibetan plateau (TP) is considered to be the water tower of Asia being the source

of many major Asian rivers such as the Yellow, Yangtze, Mekong, Salween, and

Brahmaputra river basins. The TP is characterized by a variety of elevations (with the

average of above 4000m), large area of snow mountains, glaciers, permafrost, and

mountain lakes. Studies have suggested that the surface temperature on the TP is

warming over the past 50 years, and major climate-induced changes have occurred,

such as glacier melting and permafrost degradation. However, how the climate and the

induced changes affect the hydrology and water resources in the TP is still not clear.

The contribution of snow and glacial melt to the total river runoff is not yet properly

quantified. Earlier studies suggest that the glacier-melting water is extremely important

in the Indus and Brahmaputra basins, but plays only a modest role for the other basins.

Hydrological models provide a useful approach for understanding and evaluating the

impact of climate and cryosphere changes on river runoff. In this work, we describe an

application of the Variable Infiltration Capacity (VIC) macroscale hydrology model to

simulate the land surface water process over the upstream of major rivers in the TP. A

Degree-Day glacier-melt-runoff module was incorporated into the VIC model to

represent the contribution of glacier-melting water to the total runoff. The modeled

water balance were evaluated with streamflow records with available observed

streamflow data.

Hydrologic simulations of the Upstream of Major Rivers in the Tibetan Plateau Fengge Su1, Leilei Zhang1,2, Kai Tong1,2 , Zhenchun Hao2, and Cuo Lan1

1Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China. E-mail: fgsu@itpcas.ac.cn2State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing , China

The VIC model(Liang et al., 1994;1996) was designed both for inclusion in the GCMs (General Circulation Models), and for use as a stand-alone macro-scale hydrologic model.

Model features:Model features:

The VIC model and Datasets

Source Region of Yangtze River Area : 137 704 km2 Time :1961-2005

Source Region of Yellow River Area : 121 972 km2 Time : 1961-1999

Source Region of Mekong RiverArea : 53 800 km2 Time : 1961-2000

Precipitation(mm)

Simulated (m3/s)

Observed (m3/s)

meteorological gauge stations

stream stations

R2=0.9161 R2=0.9389

R2=0.9581

Observed (m3/s)

Nash–Sutcliffe coefficient of efficiency: NSE

BasinDrainage area(km2)

Mean yearly run off(mm)NSE

Er(%)Observed Simulated

Yellow River at Tangnaihai

121972 173.65 173.01 0.8034 -0.37

Yangtze River at Zhimenda

137704 92.39 100.54 0.6505 8.81

Mekong River at Changdu

53800 295.91 251.76 0.7997 -15.23

Basin station longitude latitude time Drainage area(km2)

Yellow River Tangnaihai 100.09 35.30 1961-1999 121 972

Yangtze Zhimenda 97.13 33.02 1961-2005 137 704

Mekong Changdu 97.11 31.11 1961-2000 53 800

Salween Daojieba 98.53 24.59 1961-2000 110 224

1. Runoff over the source regions of the Yellow, Yangtze, and Mekong rivers are mostly from

summer rainfall; the contribution of snow and glacier melting is minor.

2.The model simulations (around 40 years) over the Yellow, Yangtze, and Mekong river

basins suggest that the VIC model was able to reproduce the observed streamflow reasonably

well for the basins with little glacier distribution.

3. However, the VIC model considerably underestimated the baseflow in winter. When there

is frozen soil exists within a grid, the VIC model considers the grid as a whole impermeable

surface and does not take into account the heterogeneity of the infiltration capacity within the

grid , leading to very low baseflow.

4. The glacier has to be considered in streamflow simulations for basins of Salween,

Brahmaputra, and Indus basins where there are larger distributions of glacier. We will further

test the Degree-Day glacier module in the VIC model over these basins. Future work will

focus on improving the parameterizations of frozen soil, and incorporating an energy-based

glacier module in the VIC model to improve steamflow simulations for the river basins in

the TP.

1. Multiple vegetation classes in each cell;

2. Energy and water budget closure at each time step;

3. Subgrid infiltration and runoff variability;

4. Non-linear baseflow generation

Yellow River at Tangnaihai Mekong River at Changdu

Glaciated area within each basinGlaciated area (%):Yellow: 0.11Yangtze: 0.93Mekong: 0.43Salween: 1.61 Brahmaputra: 2.17Indus: 2.2

Contribution of glacier-melting water to total runoff (%):Yellow: 0.6-0.8Yangtze: 8.8-9.2Mekong: 4.0-6.6Brahmaputra: 38Indus: 40.4-44.8

World Data Center For Glaciology and Geocryology, Lanzhou (http://wdcdgg.westgis.ac.cn/)

Immerzeel et al. 2010; Liu et al. 2007; Yang et al. 2000; Xie et al. 2003; Liu 1999; Yang and Hu 1990

33

44 Streamflow simulations for the rainfall-dominated basins

Without glacier With glacier

Yangtze at Zhimenda

Simulated (m3/s)

Relative error: Er

55 Model results with incorporating Degree-Day glacier-melt-runoff module

Salween basin at Daojieba for 1961-2000 (Area: 110 224km2)

22