4.2.4 Changes in NDVI in sub-basins
Starting from the 1970s, the Qinhe River Basin has implemented
large-scale water and soil conservation measures, with a focus on
afforestation of hillsides, creating forests for water and soil
conservation, and transforming residual forests. In this study, the NDVI
data of the Qinhe River Basin during change periods I and II were
analyzed. The average NDVI of the basin increased by 5.36%, from 0.56
to 0.59. However, the average increase rate of the sub-basin where the
reservoir is located was 6.77%. The NDVI growth rate of the upstream
No. 1 reservoir was lower than the average value of the basin, as it is
located upstream and is more affected by natural factors. Due to the
good initial vegetation coverage, the growth potential in this sub-basin
is low. On the other hand, the NDVI growth rate of the downstream No. 5
Reservoir was the same as the average value of the whole basin. The NDVI
growth rates of the No. 2, No. 3, and No. 4 Reservoirs were 6.78%,
10.53%, and 9.62%, respectively. The sub-basin where the downstream
No. 5 Reservoir is located is severely disturbed by human activities,
and the land types are frequently transformed. This explains the lack of
evident NDVI growth in this area.
Field investigations have revealed that to maintain the flood detention
capacity of the reservoir and protect the safety of the dam site, the
local government has paid more attention to vegetation restoration and
water and soil conservation measures in the upstream area of the
reservoir. This has partly contributed to the higher NDVI growth of the
sub-basins containing reservoirs than the average value of the basin
during the same period. Figure 8 illustrates the NDVI changes in the
sub-basins containing reservoirs.