2007 Annual Report - jamstec japan agency for marine-earth ...

the western North Pacific brought most of the rainfall over
Thailand in September. TCs include tropical depressions, tropical
storms, severe tropical storms, typhoons, and residual lows.
70% of the rainfall amount in September was estimated to be
associated with TCs.
The 50-year time-series of September rainfall over
Thailand showed a significant decreasing trend. TC activity
defined by 700-hPa relative vorticity, showed a weakening
trend over the Indochina Peninsula Fig.3. TC tracks also
suggested the weakening of TC activity over this area. The
long-term trend in rainfall during the late summer monsoon season
was closely associated with changes in TC activity over the
Indochina Peninsula; these changes were likely caused by
changes in the major course of TCs Fig.3. Concurrent with
the changes in TC tracks, there was a change in the TC steering
investigated by AGCM using the global vegetation maps since
1700 Ramankutty and Foley, 1999; Hirabayashi et al.,
2005. In 1700-1850, impacts of human-induced increases in
greenhouse gases and aerosols were negligible. Therefore cultivation
was the major anthropogenic disturbance to the climate
in that period. The cultivated areas in Asia for 1700-1850 were
the Indian subcontinent and China. Surface albedo was
increased and surface roughness was decreased due to land
cover/use change, leading to changes in evaporation and water
vapor convergence in those regions. As a result, monsoon precipitation
was reduced in those regions, particularly in the
Indian subcontinent, from 1700 to 1850 Fig.4. This result
is consistent with the estimation of long-term changes in Indian
monsoon precipitation by Himalayan glacier ice-cores.
Takata et al., PNAS, to be submitted
current around the Philippines archipelago and Taiwan. This led
to the TC activity over the Indochina Peninsula being inactive,
probably resulting in the long-term decrease in rainfall over
Thailand. Takahashi and Yasunari, 2008, JMSJ
Fig.4 June-August mean changes from 1700 to 1850.
a) Preciptaion (shades in mm/day) and water vapor flux at 850 hPa (unit
vector in2/s). b) Albedo (shades) and surface air temperature at 2 m
(contours in K).
b. Land-Surface Hydrological Cycle Process Group
b-1. Examination of the water budget in the Yellow River basin
In this study, we describe a hydrological model that considers
five categories of land use. Calibration and verification of
the model were carried out at two independent watersheds
Tangnaihai, 120,000 km 2 and Lushi, 6,400 km 2 . The model
results represent the hydrographs and annual runoffs at two
Fig.3 upper panel Scatterplot between September rainfall over
Thailand and TC day defined by 700-hPa relative vorticity. Rectangle, circle,
and star symbols indicate the relationship in each year during P1
1958-65, P21966-80, and P31981-95, respectively. The crosses
labeled P1, P2, and P3 show the mean relationship of each period.
lower panel Distribution of TC-appearance frequencies during P1
1958-1965 and P31981-95. Unit is times per month.
gauge stations over a relatively long-term period 18 years at
Tangnaihai and 21 years at Lushi. The Nash-Sutcliffe efficiency
coefficients for monthly discharge were 0.87 at
Tangnaihai for the period of 1980-1997 and 0.84 at Lushi for
the period of 1980-2000. The model was applied to other watersheds
of the Yellow River basin above Huayuankou station, and
a-3. Evaluation of impacts of land cover/use change by cultivation
in pre-industrial period on Asian monsoon climate
Impacts of Land cover/use change by cultivation on Asian
monsoon climate in the pre-industrial period, 1700-1850, was
water budget components in each region were analyzed. Water
use for agricultural irrigation was stable throughout the entire
simulation period. A numerical experiment of water conservation
for the whole basin above Huayuankou station demonstrat-