[Insert Figure 7 here]
3.5 Spatial linkage of increased precipitation to
enhanced water vapor
circulations
Previous studies have identified the
main sources of moisture for precipitation in the TP, including regions
from the Indian sub-continent to the Southern Hemisphere, the Bay of
Bengal and the northwestern part of TP. (Chen et al. 2012; Zheng et al.
2019).
It
is proven that these circulation changes in the increase or decrease of
different moisture sources provide favorable water vapor conditions for
rainfall on the TP. Thus, the
changes in moisture source contributed to different precipitation
changes across the entire TP during different periods. As indicated in
the preceding results, the lake water levels increased rapidly during
the period 2016-2018 relative to the previous stage. The phenomenon was
analyzed with the distribution of water vapor transport on the TP.
The differences can be observed with the four years when the water vapor
is transported by abnormal northwesterly, southeast wind and south wind
in 2015, 2016, 2017 and 2018, respectively
(Fig.
8B, Fig. 8C, Fig. 8D, Fig. 8E). In comparison, the total water vapor
increases with the most significant anomaly in 2017-2018. The moisture
transported to the northwestern part of the TP has increased
significantly in last several years due to the strengthening of the
westerlies. In this study, precipitation in the NTP is more obviously
influenced by the East Asian monsoon and the Indian summer monsoon. The
summer monsoon circulation was enhanced, and the meridional water vapor
transport from the south plateau to the Bay of Bengal was significantly
enhanced. Similarly, precipitation in the CTP was more influenced by the
Asian summer monsoons. In addition, the water vapor flux from the Indian
Ocean to the plateau was enhanced. From Fig. 8D, we can also find that
there is a phenomenon of internal water vapor circulation and retention,
which might cause water vapor subsidence and significant rainfall over
the western CTP. In general, the change in water vapor transport during
the study period supports the changing characteristics of precipitation
and lake level for TP as analyzed above.
In this study, as shown in Fig. 6
and Table 3, we can find the rising rates of lake levels at different
parts of TP are different. The water level rising rates for some typical
lakes exceed 0.80 m/a in the northern TP such as XijingUlan Lake,
Mingjing Lake, Lexiewudan and Ayakkum.
There
are some glaciers distributed in the northern TP, and there is rich
rainfall in the rainy season. Therefore, the rapid increase of water
level is affected by both rainfall and glacial meltwater. The rising
rate of lake level in central TP is mainly divided into two categories.
For example, at Zhari Namco and Dagze Co in the western CTP, the rising
rates are 1.34 m/a and 1.43 m/a respectively. The rising rates of lakes
in the central and eastern CTP are slower, generally less than 0.40 m/a.
The reason for this difference may be because the phenomenon of internal
water vapor circulation and retention mainly occur in the western CTP.
In NWTP which was mainly affected by the westerlies, the distinction in
water vapor transport distribution in different years led to a
significant difference in the water level rising rates. As indicated in
the preceding texts, the differences in water level rise rate are caused
by different
water
vapor transport patterns and main sources in different regions.