Other Abstract | As called “the Third Pole of the earth”, the Tibetan Plateau influences the climate of China,
eastern Asia, even the north hemisphere greatly. It is slso the source for big rivers in China as a
lot of glaciers exist there. The ecosystem is quite vulnerable due to the cold and arid environment.
With climate warming, many problems such as glacier retreat, extreme climate and
desertification occurred often, which caused by the changes in heat and water conditions. But
few systematic researches had been conducted in some typical regions due to the formidable
environment. The western Mts Nyainquentanglha is the dividing line of cold and warm climate
on the plateau, where glacier, frozen soils, wetland and the Nam Tso lake, the biggest lake in
Tibet, are, and is a ideal site for scientific studies. This study investigated on air and soil
hydrothermal processes and its NDVI response, as well as the changes with climate warming,
which may improve the understanding on energy and water balance and exchange and
environmental evalution in the mountain areas of the plateau.
1 Ground surface hydrothermal processes in the western Nyainquentanglha
Based on meteorological data from six automatic weather stations, the seasonal and
diurnal variations of air temperature (Ta), precipitation and relative humidity (RH) are
investigated during 2005-2007, analysis shows that Ta and RH are controlled by altitude firstly.
Ta rises quickly and drops slowly in a day. The amplitude of diurnal variation is largest in spring
in the region near Nam Tso lake, so do at the place where no glacier is found than that of glacier.
The effect of Nam Tso lake is quite evident and make the difference between Ta and ground
surface temperature larger in cold season.The RH is also influenced by the ground surface
condition, aspect, wind direction, which is different in different area and season.
The similar daily and diurnal precipitation variations demonstrated the southern and
northern slopes of Nyainquentanglha are controlled by the same precipitation processes. Due to
the vapor and disturbance from the lake and topography, differences exist in the precipitation
amount, oscillation periods and diurnal variation processes. The frequency of precipitation near
the lake is higher than other areas, the precipitation increases from southwest to northeast and the
diurnal variations are different in different part of the lake.
2 Soil hydrothermal processes in the western Nyainquentanglha
Based on soil temperature and moisture data, the results show the soils freeze later and thaw
earlier in the western Nyainquentanglha than that in other regions of Tibetan Plateau. The
altitude effect of soil thermal condition is evident. The annual range, temporal distribution of the
transfer rate of heat within soil and diurnal variation are quite different at different measurement
site due to the impact of snow cover, vegetation and soil moisture. The soil moisture is
influenced by soil temperature, snowcover, precipitation, evaporation, soil characteristics and
ground water, no evident trend exists in the amount and the soil depth. It shows evident an abrupt
change during freezing and thawing periods and get lost after freezing in northern slope except
for the place near the lake. A further study indicates the soil hydrothermal condition is influenced
by unfrozen water and the infiltration of precipitation greatly and gets weak impact from the
infiltration of snow meltwater.
3 The NDVI response to hydrothermal condition and climate change in the western
Nyainquentanglha
The vegetation grows from June to October. The growth of vegetation is controlled by
temperature and water together in southern slope and by temperature evidently in northern slope
at a growth period, while it is inverse at monthly scale. It is relied by precipitation greatly during
growth season.
Climate warming is evident from 1963 to 2006 in the study region. The air temperature
increase most quick in winter, then in autumn. Comparison, it is faster in northern slope than that
in southern. As a result, the frozen soil degraded seriously, the ground temperature increased
about 1.1 ℃at 0 cm depth and 0.8 ℃ at 40 cm depth respectively before and after 1985, it
shown a maximum increase about 3.4 ℃ at 80 cm depth from 1963 to 2006. The decrease rate
of the maximum freezing depth is higher than the average rate in the Tibetan Plateau. The
evident increase of winter precipitation may result in spring flood. But the vegetation is better
than before due to the climate warming. |
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