Vegetation Activity Trend and Its Relationship with Climate Change in the Three Gorges Area, China

Abstract

Based on SPOT/VGT NDVI time series images from 1999 to 2009 in the Three Gorges Area (TGA), we detected vegetation activity and trends using two methods, the Mann-Kendall and Slope tests. The relationships between vegetation activity trends and annual average temperature and annual total precipitation were analyzed using observational data in seven typical meteorological stations. Vegetation activity presents a distinctive uptrend during the study period, especially in Fengjie, Yunyang, Wushan, Wuxi, and Badong counties located in the midstream of the Three Gorges Reservoir. However, in the Chongqing major area (CMA) and its surrounding areas and Fuling, Yichang, and part of Wanzhou, vegetation activity shows a decreasing trend as a result of urban expansion. The NDVI has two fluctuation troughs in 2004 and 2006. The annual mean temperature presents a slight overall upward trend, but the annual total precipitation does not present a significant trend. And they almost have no significant correlations with the NDVI. Therefore, temperature and precipitation are not major influences on vegetation activity change. Instead, increasing vegetation cover benefits from a number of environment protection policies and management, and ecological construction is a major factor resulting in the upward trend. In addition, resettlement schemes mitigate the impact of human activity on vegetation activity.

The Driving Force Analysis of NDVI Dynamics in the Trans-Boundary Tumen River Basin between 2000 and 2015

“…These results show that the overall growth of this index across the whole growing season was not significantly affected by these climatic variables when the whole TRB region is taken into account. This result suggests that vegetation change cannot be fully explained by climatic factors in the entire TRB region, in addition to temperature and precipitation, environmental protection initiatives including anthropogenic activities and ecological restoration have also contributed to NDVI changes especially in regions where significant positive correlations with climatic factors were not recovered [18,31].…”

“…This means that regions where no significant positive correlation between this index and climatic factors is present can be influenced by anthropogenic effects [18,31]. A significant decreasing trend in residuals indicates the human-induced vegetation degradation [20,22].…”

“…In addition, climatic parameters (temperature and precipitation), environmental protection policies and management strategies, human activities, and ecological construction projects are all also major factors leading to changes in vegetation dynamics [18]. For example, environmental protection policies can cause increases in vegetation cover as the conversion of croplands to forests alter plant productivity.…”

Temperature changes in Three Gorges Reservoir Area and linkage with Three Gorges Project

“…We found an extended cooling area (~5 km away from the reservoir boundary, light green in Figure 7b) in DTGRA in summer compared with those in other seasons. Since dam impounding, ecological protection projects in the TGRA have resulted in substantial vegetation restoration, mostly from cropland to forest [Han et al, 2013;Xu et al, 2013;J. Zhang et al, 2009;Zhang et al, 2011Zhang et al, , 2012.…”

“…The Three Gorges Reservoir (TGR) went through a long impounding period from 2003 to 2010 when its water area expanded from 408 km 2 to 1064 km 2 . In addition, large‐scale immigration (about 1.25 million people) and government‐initiated ecological protection projects have led to substantial land cover changes in the Three Gorges Reservoir Area (TGRA), with an urban land area increase of 398 km 2 from 1992 to 2007, and a conversion of cropland to forest/glassland at 1020 km 2 from 1993 to 2008 [ Han et al , ; Xu et al , ; J. Zhang et al , ; Zhang et al , , ]. Such large‐scale land cover changes are likely to have affected the local climate [ Dale , ; Kalnay and Cai , ; Pielke et al , ].…”