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.
Highlights
IntroductionOver the last three to four decades, using the satellite-observed leaf area index (LAI) or normalized difference vegetation index (NDVI), several researchers have found that the vegetation greenness has been increasing in most parts of the Northern Hemisphere, especially in China [1,2,3].Increased vegetation greenness, resulting from watershed management projects such as afforestation, reforestation, and improved agricultural practices, can improve terrestrial ecosystem productivity [4,5].some studies have shown that vegetation greening can reduce watershed water yield ( referred to as streamflow or runoff); it can reduce the water resources available for humans [1,6,7].in arid and semi-arid areas, numerous studies have suggested that increased vegetation greenness can induce water demand conflicts, but few studies have investigated water yield responses on increased vegetation greenness in humid areas [4,8].If unpolluted water within a region is less than that region’s demand by social-economic systems, a water crisis will arise [9]
Lakegroundwater watershed.is The reason is that the soil and the shallow groundwater has a positive plentiful [48] and where the watershed management projects were effective [2,22]. effect on new vegetation growthand because the PoyangofLake watershed is in a humidvaried region where the shallow
We investigated the effects of vegetation greenness on water yield in the Poyang
Summary
Over the last three to four decades, using the satellite-observed leaf area index (LAI) or normalized difference vegetation index (NDVI), several researchers have found that the vegetation greenness has been increasing in most parts of the Northern Hemisphere, especially in China [1,2,3].Increased vegetation greenness, resulting from watershed management projects such as afforestation, reforestation, and improved agricultural practices, can improve terrestrial ecosystem productivity [4,5].some studies have shown that vegetation greening can reduce watershed water yield ( referred to as streamflow or runoff); it can reduce the water resources available for humans [1,6,7].in arid and semi-arid areas, numerous studies have suggested that increased vegetation greenness can induce water demand conflicts, but few studies have investigated water yield responses on increased vegetation greenness in humid areas [4,8].If unpolluted water within a region is less than that region’s demand by social-economic systems, a water crisis will arise [9]. Increased vegetation greenness, resulting from watershed management projects such as afforestation, reforestation, and improved agricultural practices, can improve terrestrial ecosystem productivity [4,5]. Some studies have shown that vegetation greening can reduce watershed water yield ( referred to as streamflow or runoff); it can reduce the water resources available for humans [1,6,7]. In arid and semi-arid areas, numerous studies have suggested that increased vegetation greenness can induce water demand conflicts, but few studies have investigated water yield responses on increased vegetation greenness in humid areas [4,8]. Prior studies of water yield responses on vegetation greening were concentrated on some water-limited arid and semi-arid regions [10,11,12]. Feng et al [13] showed that water yield decreased by 1–48 mm year−1 in 37% of the regions of the Loess
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