377 / 2024-02-29 23:42:23

Changes in vegetation coverage in the Jingjiang Reach and its response to the altered flow-sediment regime

Vegetation coverage; flow-sediment regime; remote sensing imagery; Three Gorges project

Since the operation of the Three Gorges Project (TGP), the flow and sediment regime entering the downstream channel has been altered greatly, which also cause great impacts on the growth environment of vegetation. In the current study, the spatio-temporal dynamic process of vegetation growth in the Jingjiang Reach (JJR) was analyzed based on long-series of remote sensing imageries, and the response of vegetation growth to the altered flow and sediment conditions was further investigated. It is found that (i) the vegetation coverage area of the JJR showed a significant increasing trend, with the maximum vegetation coverage increasing from 22.8 km² in 1995 to 36.2 km² in 2021 and the minimum vegetation area increasing by about 30%. Moreover, the value of Fraction Vegetation Coverage (FVC) increased from 0.37 to 0.48 in 1995-2021; (ii) Vegetation expansion and density increase mainly occurred in the zone with the submergence frequency less than 30% and the average submergence depth less than 2.5 m, which was taken as the suitable habitat for vegetation growth. At the third stage of the TGP operation (2014-2020), the area suitable for vegetation growth increased by about 30% and 25% than other two stages in 2003-2008 and 2008-2014. The reasons mainly contains two aspects. On the one hand, the inundation duration of floodplain was about 30 days shorter than that before the TGP operation, owing to the joint effects of declining water level under equal discharges and decreasing occurrence frequency of flood discharges. On the other hand, sediment deposition occurred on the floodplain, which increased the surface elevation and provided necessary nutrients for vegetation growth.