Increased Vegetation Greenness Aggravates Water Conflicts during Lasting and Intensifying Drought in the Poyang Lake Watershed, China

Abstract

An increase in vegetation greenness can improve ecosystem productivity, but also reduce the water supply, creating the potential for conflicting water demands between ecosystems and humans. This problem has been well-assessed and is most evident in dry environments. However, in humid regions, the potential effects of vegetation greenness on water yields under drought conditions are not well understood. To address this gap, we focused on the Poyang Lake watershed in the humid region of southern China. Based on the Standardized Precipitation Evapotranspiration Index and a satellite-derived leaf area index dataset during the growing seasons of 1984 to 2013, several typical dry growing seasons were selected as the study conditions. An existing Water Supply Stress Index model was modified to investigate how the changes in vegetation greenness affected water yield and to explore potentially conflicting water demands between ecosystems and humans under drought conditions. Our results showed that an increase of 20-80% in vegetation greenness generally resulted in a reduction of 3-27% in water yield under drought conditions. Large reductions in water yield mainly were observed in forested areas due to large increases in forest greenness. Moreover, increased vegetation greenness caused a 2 to 3 times greater reduction in water yield during continuing and intensifying droughts than during a short moderate drought period. Thus, in this study, during continuing and intensifying droughts, increased vegetation greenness can cause or aggravate water conflicts in sub-watersheds with high forest cover and high human water demands. Therefore, given the increasing frequency of extreme climatic events, afforestation with a targeted approach should be implemented as it would provide the most benefits. In addition, selective harvesting in forested areas with high density could be an effective strategy to maintain water supply in humid regions.

Contrast Effects of Vegetation Cover Change on Evapotranspiration during a Revegetation Period in the Poyang Lake Basin, China

“…A high vegetation cover could also enhance the runoff yield due to precipitation interception of a large leaf area of canopy. A recent study has reported that increased vegetation greenness resulted in reduced water yield, which may elevate or aggravate water conflicts in droughts [19]. Our results demonstrate that vegetation restoration overall favors annual runoff yield, and its water retention plays a positive role in supplying water resources for the Poyang Lake Basin and downstream areas of the Yangtze River as well.…”

“…In addition, the increases of vegetation cover areas all led to increases in actual ET [11]. Some other studies have also supported this view and demonstrated that an increased vegetation cover could reduce runoff because of an enhanced canopy interception and ET [12][13][14][15][16][17][18][19]. In contrast, several studies have pointed to a negative relationship between vegetation cover and annual ET at multiple spatial scales [15,20].…”

Vegetation Greening Significantly Reduced the Capacity of Water Supply to China's South-North Water Diversion Project

“…The climate regime and vegetation cover make the UHRB more likely to suffer hydrological drought, and the water cycle can be largely influenced by vegetation dynamics. While the WY of the Poyang Lake basin would only decrease approximately 3% even under an extreme greening scenario (Guo et al, 2008;Tang et al, 2018), the effects of vegetation greening on the water cycle in the UHRB are much larger than this, with a decrease in WY up to 25% for comparable levels of vegetation greening (Figure 5c).…”

Effects of Revegetation on the composition and diversity of bacterial and fungal communities of sandification land soil, in Southern China.

“…In China, most degraded or desertification lands are distributed in the northern region, that is, the arid and semiarid regions (Chen et al , 2004, Zhang et al , 2019. While in southern China, including the Poyang Lake watershed which belongs to the humid area also have the sandification land (Zhu & Cui, 1996, Chen et al , 2004, due to the joint influence of climate and human factors (Tang et al , 2018).…”

“…In northern China, Pinus sylvestris (Zhao et al , 2020) and Pinus tabulaeformis (Liu et al , 2019a, Liu et al , 2019b, Wang et al , 2019 were planted to control soil degradation or desertification. Likewise, since the 1980s, slash pine (Pinus elliottii ) has been widely planted to control and restore sandy lands in the Poyang Lake watershed (Zou, 1990, Tang et al , 2018. However, reforestation mainly relies on single-species monoculture, and pure forest plantation would cause soil quality decline and plantation degradation in both degraded and non-degraded land (Liu et al , 2012b, Wu et al , 2015, Zhao et al , 2020.…”