21st century climate change impacts on the hydrology of upstream of major rivers in the
Tibetan Plateau
Fengge Su1, Xiaolan Duan1,2, Leilei Zhang1,2, Zhenchun Hao2, and Cuo Lan1
1Institute
2State
of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China. E-mail: [email protected]
Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing , China
1 Abstract
Major Asian rivers including Indus, Ganges, Brahmaputra, Irrawaddy, Salween,
Mekong, Yellow, and Yangtze originate from the Tibetan Plateau (TP). These rivers
3
Downscaling for climatologic forcing
4 Hydrologic response to climate change
Spatial pattern of seasonal precipitation (left) and temperature (right) change factors for the A2
2080 scenario with respect to the period 1961–1990
Seasonal cycle of VIC simulated evapotranspiration (left) and runoff (right) for
the 1970s, 2020s, 2050s, and 2080s for scenarios A2 and B1 for the five river
basins
support billions of people downstream, and the TP is therefore considered as the water
tower of Asia. Changes of climate factors (e.g., temperature and precipitation) and the
induced changes (e.g, melting of glacial and permafrost) may have substantial impacts on
the hydrological cycle in the TP. Therefore, quantifying the potential impacts of future
climate changes over the TP is essential to assist policy-makers and water managers in
adopting strategies reflecting the state of scientific understanding of the likelihood. In
this work, temperature and precipitation projected by 20 general circulation models
(GCMs) from emission scenarios B1 (lowest emission scenario) and A2 (mid-high
emission scenario) were used to characterize the potential climate changes over the TP
for 2011-2100. Outputs from the 20 GCMs were downscaled by using the delta method,
and were used to force a land surface hydrology model. The hydrology model was
applied to investigate the impacts of climate change in the 21th century on the hydrology
of upstream of five major river basins in the TP –the Yellow, Yangtze, Mekong,
Salween, and Brahmaputra.
2
Data and methodology
Precipitation in the north and northeast of TP is projected to increase (20-50%) during Nov-May.
Largest decrease (10-30%) is projected to occur in the south and southeast of TP during Nov-Jan, in
the south and southwest during Feb-Apr, and northwest during May-Sep.
Greatest warming is projected to occur in cold months (Nov-April) for most regions of the TP with the
warmest (5.0-6.0ºC) appearing in the middle. The northwestern TP is projected to warm greatly (45.0ºC ) throughout the year. The southeast part is projected to warm the least (3-3.5ºC) for all seasons.
Basin-wide precipitation (left) and temperature (right) change factors for the 2020s, 2050s, and 2080s
scenarios A2 and B1 relative to the 1961-1990 average for the upstream of five river basins
1
2
4
The runoff response to the climate changes in the 21th century varies across seasons and basins. On the
annual basis, runoff is projected to decrease 5-20% for the source regions of the Yellow, Yangtze, and
Mekong river basins for all scenarios relative to the 1970s . While mean annual runoff is projected to
increase 10-15% for the upstream basins of the Brahmaputra and Salween.
Spatial pattern of projected runoff (left) for the 2020s, 2050s, and 2080s for
scenarios A2 and B1, and the changes (right) with respect to the 1970s
3
5
Control Station
Longitude
Latitude
Drainage Area (km2)
1.Yellow River
Tangnaihai
100.09
35.30
121 972
2. Yangtze
Zhimenda
97.13
33.02
137 704
3. Mekong
Changdu
97.11
31.11
53 800
4. Salween
Daojieba
98.53
24.59
110 224
Nuxia
94.34
29.27
201200
Basin
5. Brahmaputra
There is a strong spatial variation in the projected runoff and the changes within and across the basins.
Hydrological model: VIC
Data: (1) GCM outputs of monthly P and T for 1961-1990 and 21st century for
scenarios A2 and B1; (2) Daily P, Tmax, Tmin, and Wind from 158 meteorological
gauge stations for 1961-1990
Delta at 2°×2°
Downscaling method: Delta method
Re-grid
1970s (1961-1990); 2020s (2011-2040)
2050s (2041-2070); 2080s (2071-2100)
Delta at 1/12°×1/12°
 T  T2080 s , monthly  T1970 s , monthly
P 
Observed P, T
P2080 s ,monthly
P1970 s ,monthly
T2080 s ,daily  To ,daily  t
Vegetation, Soil type, DEM
P2080 s , daily  Po ,daily  p
Where To ,daily and Po ,daily are the observed
daily temperature and precipitation, respectively.
Likewise we do the same for the time slice of
2020s and 2050s.
Future climate forcing
VIC model
Hydrologic response
Largest warming (up to 5.5ºC) is projected to occur in cold seasons for all the basins and scenarios.
Precipitation is projected to increase (up to 30%)in winter for the Yellow and Yangtze, in winter and
spring for the Salween and Mekong, in summer and autumn for the Brahmaputra.
Seasonal cycle of
precipitation and
temperature for
the 2020s, 2050s,
and 2080s for
scenarios A2 and
B1 for the
upstream of the
Yellow, Yangtze,
Brahmaputra,
Salween, and
Mekong river
basins.
5
1.
Summary and Further work
Temperatures of the five selected source region basins in the TP are projected to increase
in the 21st century for all scenarios relative to the 1961-1990 average, with the largest
warming (up to 5.5ºC) occurring in cold seasons.
2. Precipitation over the five source region basins is generally projected to increase in the
21st century for all scenarios. However there is a strong seasonality for the precipitation
changes and the change rates vary among basins and scenarios.
3. Runoff changes are mostly the results of the combined changes in both precipitation and
temperature. However the sensitivity of runoff changes to precipitation and temperature
varies among basins.
4. In this analysis, the VIC model does not consider the glacier-melt-runoff process. We are
currently developing a glacier-melt model which will be incorporated to VIC. The
improved VIC model will be used to investigate the impacts of future climate changes on
the hydrology of glacier-dominated river basins in the Tibetan Plateau.