Sustainable Agriculture and Food: Four volume set (Earthscan Reference Collections)

460 Modern Agricultural Reforms

composed of plateau and basins with elevations of 1000–2000m. Eastward from
that line and extending to the mouth of the Yangtze River is the third great step.
In the lower Yangtze River basin, the third step staircase, there are extensive plains
largely below 50m. This region is famous for grain production. The Yangtze River
has a vast drainage area of 1.8 × 10^6 km^2 and a particularly heavy annual run-off of
9.79 × 10^11 m^3 , accounting for 37.2 per cent of the national total. In terms of aver-
age flow, the river has a water resources reserve of 2.3 × 10^8 kw, or 42.5 per cent
that of the whole country. The average annual flow of the Yangtze River accounts
for over 30,000m^3 /s, or 17 times that of the Huanghe River. Table 18.16 shows the
basic features of different sections of the river.
In order to relieve the Yangtze River flood problem, large-scale hydrological
works have been done since 1949. Dykes along its main stream and its main tribu-
taries have been repaired, raised or strengthened. The Jingjiang flood diversion
project, the Hanjiang flood diversion project and other flood-storage projects have
been built along its middle reaches, where the area is often hit by unusual floods.
Many lakes have been dredged, and this has increased the capability of the Yangtze
River to prevent flooding. At the same time, more than 40,000 small reservoirs for
irrigation, and over 500 big and medium-sized reservoirs for multi-purpose utiliza-
tion have been built. Currently, the Three Gorges Project, attracting worldwide
attention, is underway, which will play an important role in preventing natural
disasters and providing the electric power for economic construction and develop-
ment of the Yangtze River basin.
The climate of the middle and upper reaches of the Yangtze River basins is
characterized by a vertical differentiation of climatic zones (Table 18.17). How-
ever, most of the areas located between 2000–3000m belong to a subtropical zone
with warm winters, cool summers and spring-like weather for all four seasons.
Although climatically the region does not have marked contrasts in seasons, it does
have notable differences in dry and wet weather. Generally, it is dry from Novem-
ber to April and wet from May to October.
The forest vegetation in different sections of the Yangtze Basin varies signifi-
cantly. In the upper reaches of the Yangtze River, forest vegetation in some areas has
maintained its natural structure and the latitudinal differentiation of the vegetation

Table 18.16 The basic hydrological features in different sections of the Yangtze River

Section Upper

reaches

Middle

reaches

Lower

reaches Total

Length (km) 4529 927 844 6300

(%) 72.0 14.7 13.3 100

Drainage area (km^2 ) 100.55 67.74 12.56 180.85

(%) 55.6 37.6 6.8 100

Annual discharge (10^8 m^3 ) 4543 4636 615 9794

(%) 46.4 47.3 6.3 100