Vegetation Water Use Efficiency Research Articles

Spatial and Temporal Patterns of Vegetation Water Use Efficiency and Its Response to Climatic and Environmental Factors in Gansu Province

Vegetation water use efficiency (WUE) is a crucial indicator for elucidating the interconnections between the carbon and water cycles of ecosystems and for discerning the response of vegetation ecosystems to climate change. Gansu Province in northwestern China is facing significant ecological water-related challenges. However, the response of vegetation WUE to climate environmental factors in this region remains unclear. In this study, the MODIS vegetation gross primary productivity (GPP) and evapotranspiration (ET) datasets were used to calculate the vegetation WUE in Gansu Province and, combined with meteorological data, Theil–Sen median trend analysis and partial correlation analysis were used to determine the spatial and temporal characteristics of vegetation WUE in this region and its response to climate environmental factors. Finally, the random forest model was used to rank the importance of climate environmental factors. The results indicate the following: (1) The average values of vegetation WUE, GPP, and ET in Gansu Province from 2000 to 2020 were 1.46 gC·mm−1·m−2, 510.22 gC·m−2, and 343.68 mm, respectively, and their spatial distribution was high in the southeast and low in the northwest, which was closely related to the distribution of vegetation in the region. (2) Over the past 20 years, the vegetation WUE in this region showed a slowly decreasing trend in general, with a decrease rate of 16.57%. There were significant differences in the WUE of different vegetation types, among which forest WUE was the highest and grassland WUE the lowest. (3) The trend prediction of WUE in Gansu Province was performed by using the rescaled extreme difference method, and the Hurst index was 0.45, which means that the vegetation WUE in this region is expected to increase in the future. (4) In general, precipitation was the main factor influencing the change in vegetation WUE in Gansu Province, followed by vapor pressure deficit (VPD), temperature, and soil moisture. This study provides strategy support for the coupling process of vegetation ecosystems and the sustainable development of agriculture and animal husbandry in Gansu Province and has scientific reference value for promoting and planning the sustainable development of vegetation in arid and semi-arid areas.

Dissecting the characteristics and driver factors of potential vegetation water use efficiency in China

While large-scale vegetation greening in China has substantially influenced global vegetation dynamics, the specific impact of this restoration on water use efficiency (WUE) remained inadequately understood. This study employed both the Geodetector and structural equation modeling (SEM) methods, utilizing the Lund-Potsdam-Jena (LPJ) Global Dynamic Vegetation Model, to explore the contributions of various driving factors to China's potential vegetation WUE from 1982 to 2019. The results indicated: (1) there existed considerable further potential for vegetation recovery nationwide. Among them, the Loess Plateau, Inner Mongolia Plateau, and northern Xinjiang had relatively high potential for vegetation recovery. This potential was further amplified by the significant prospects for enhancing WUE in these areas; (2) The application of the Geodetector method revealed that the normalized difference vegetation index (NDVI) explained over 40 % of the variation in potential vegetation WUE in China, exerting a greater influence than climatic factors. In arid/semi-arid regions, precipitation (PRE), NDVI, and vapor pressure deficit (VPD) significantly influenced WUE. Temperature (TEM) was the dominant factor affecting WUE in humid and humid/semi-humid regions; (3) Utilizing the SEM analysis method, it was evident that NDVI exerted the most substantial direct positive influence on potential vegetation WUE in China, whereas VPD and PRE had notable negative impacts. In arid/semi-arid regions, PRE emerged as the primary determinant of WUE. Conversely, in regions where water resources were not limiting, TEM and VPD exerted a more pronounced influence on potential vegetation WUE. This indicated that while vegetation restoration generally enhanced potential vegetation WUE, other factors such as PRE, TEM, and VPD played critical roles in different climatic zones, shaping the regional variations in WUE.

Improved water use efficiency of vegetation due to carbon fertilization not translating to increased soil moisture in India

Soil moisture (SM) plays a critical role in land–atmosphere interaction. Literature shows that the CO2 fertilization effect (CFE) governs vegetation dynamics and its interactions with the atmosphere. However, the impacts of changing vegetation properties due to CFE, on SM, specifically in India, remains unexplored. Comparing Land-hist (observed CO2 concentration) and Land-cCO2 (constant preindustrial CO2 concentration) simulations with the same meteorological forcings from the Land Use Model Inter-comparison Project (LUMIP), we found that changing vegetation due to CFE impacts SM following two pathways. Enhanced water use efficiency (WUE) due to CFE seeks to ameliorate SM by regulating transpiration. Conversely, elevated CO2 increases leaf area index and plant water use, ultimately leading to a decrease in SM due to the combined impacts of CFE in India. This reduction is most prominent in arid regions, where we observe a decline in SM particularly during dry periods. Our study highlights the need to consider plant physiology in land surface modeling under increased CO2 concentration.

Does vegetation greening have a positive effect on global vegetation carbon and water use efficiency?

Terrestrial ecosystems have undergone significant changes as a result of climate change, profoundly affecting global carbon and water cycling processes. Notably, the synergistic changes in vegetation carbon use efficiency (CUE) and water use efficiency (WUE) and their response to patterns of climate change over the last 40 years are unknown. Therefore, in this study, global vegetation WUE and CUE were inverted using Gross primary productivity (GPP), Net primary productivity (NPP) and total evaporation (ET) data from 1981 to 2019 to reveal their temporal and spatial patterns of change through trend analysis and stability analysis. A stepwise regression algorithm was used to reveal the potential driving law of environmental factors on vegetation WUE and CUE. The results shows that (1) From 1981 to 2019, the global vegetation WUE and CUE showed in a relatively stable state, and the trends of WUE and CUE were -0.00004/year and 0.006 g C m−2 mm−1/year, respectively; (2) the greening of vegetation was the most important cause of the changes in WUE and CUE, and the driving force of rain and heat conditions on the CUE of vegetation was smaller than that of solar radiation and soil water, the regions where CO2 is the dominant factor affecting CUE and WUE are mainly in the north temperate zone; (3) the region of synergistic growth of WUE and CUE accounts for about 31.38 % of the global terrestrial area, and this pattern of change suggests that the global vegetation carbon sink potential is huge, and the popularization of vegetation planting patterns under the synergistic growth of CUE and WUE should be strengthened. The research has shown that vegetation greening is a key factor influencing changes in the WUE and CUE of vegetation, therefore, the implementation of ecological engineering will be an important step in combating climate change.

Soil water content and vapor pressure deficit affect ecosystem water use efficiency through different pathways

Ecosystem water use efficiency (WUE) quantifies the amount of carbon assimilated per unit of water consumed and elucidates the trade-off between water loss and carbon gain at the ecosystem level. Numerous studies have highlighted the significant impact of low soil water content (SWC) and high vapor pressure deficit (VPD) on WUE. However, the underlying mechanisms driving these effects differ markedly. The intensifying coupling between land and atmosphere accentuates the distinctive co-occurrence of low SWC and high VPD, posing challenges in disentangling the respective influences of these two water stressors. Consequently, a clear understanding of the independent responses of ecosystem WUE to SWC and VPD remains elusive. Using meteorological and flux data from FLUXNET’s eddy-covariance sites, we investigated the impact of SWC and VPD on ecosystem carbon–water fluxes and proposed potential pathways through which SWC and VPD influence WUE. We deconstructed WUE into intrinsic WUE of vegetation (GPP/T) and the ratio of transpiration to evapotranspiration (T/ET). Our findings revealed that WUE exhibited greater sensitivity to VPD dynamics compared to SWC. The sensitivity of WUE to SWC stemmed from the responsiveness of T/ET to SWC, especially under high VPD conditions. Conversely, the sensitivity of WUE to VPD emanated from the impact on GPP/T. SWC and VPD exerted distinct effects on ecosystem WUE through different pathways.

Variations of water, carbon isotopic characteristics and intrinsic water use efficiency of vegetation in the typical beach wetland of Lake Poyang, China

Variations of water, carbon isotopic characteristics and intrinsic water use efficiency of vegetation in the typical beach wetland of Lake Poyang, China

Compensatory response of ecosystem carbon-water cycling following severe drought in Southwestern China

Climate change has increased the frequency and length of droughts, but many uncertainties remain regarding the impacts of this aridification on terrestrial ecosystem function. Vegetation water use efficiency and carbon sequestration capacity are crucial determinants that both respond to and mediate the effects of drought. However, it is important to note that the consequences of drought on these processes can persist for years. A deeper exploration of these “drought legacy effects” will help improve our understanding of how climate change alter ecosystem carbon-water cycling. Here, we investigate the spatial patterns of drought legacy effects on remotely-sensed vegetation greenness (NDVI), net primary productivity (NPP) and water use efficiency (WUE) in southwestern China, a biodiversity hotspot that was impacted by an extreme drought in 2009–2010, with a particular focus on the tradeoff between WUE and NPP. Despite widespread negative drought legacy effects in NDVI (impacting 61.26 % of the study region), there was a general increase in NPP (58.68 %) and a decrease in WUE (67.53 %) in the year following drought (2011). This drought legacy effect was most evident in forests, while drought legacies in grasslands were less common. Drought legacies were also most apparent in relatively warm and humid areas. During the study period (2002 to 2018), we found that drought impacts on WUE also lagged behind changes in NPP by 1–2 years in forests, which highlights how drought legacies may manifest differently across ecosystem processes. Our study demonstrated that severe drought conditions may significantly affect the carbon sequestration capacity and water use efficiency of vegetation in southwestern China, and that forests may compensate for the detrimental effects of water stress by increasing water use and biomass growth after drought episodes.

Differences in soil water storage, consumption, and use efficiency of typical vegetation types and their responses to precipitation in the Loess Plateau, China

After massive afforestation, the Loess Plateau is facing the severe challenge of water shortages. Water use efficiency (WUE) is an important indicator of plant drought resistance, and high WUE is an important way to reconcile the contradiction between vegetation growth and soil water consumption (SWC). Different vegetation types significantly influence hydrological cycle process and WUE. In this study, the Biome-BGC model was used to simulate and analyze the soil water storage (SWS), SWC, and WUE of 3 typical vegetation types in the Loess Plateau from 2005 to 2020. The results showed that the order of SWS of different vegetation types from largest to smallest was grassland (GL, 81.82 mm/day), abandoned farmland (AF, 66.92 mm/day), and Robinia pseudoacacia forest (RP, 55.64 mm/day); SWC was RP (480.09 mm/year), GL (464.68 mm/year), and AF (421.79 mm/year); WUE was RP (2.37 gC/kgH2O), GL (1.10 gC/kgH2O), and AF (0.60 gC/kgH2O). GL showed a better water retention capacity. Precipitation recharge did not meet the full SWC of vegetation. In years of high vegetation growth, as well as in the dry season when water was scarce, both RP and GL showed varying degrees of water deficit. Correlation analysis revealed that a positive effect of precipitation on WUE has a threshold effect, and the thresholds range from approximately 15–50 mm/day for RP, 15–25 mm/day for GL, and no clear pattern for AF. Overall, in water-stressed areas, a large expansion of forest land should be reduced and GL should be increased. In seasons and areas where vegetation is growing vigorously or extremely arid, irrigation regarding precipitation thresholds should be carried out to improve the WUE of vegetation and promote the sustainable development of regional ecology.

Recent Response of Vegetation Water Use Efficiency to Climate Change in Central Asia

Quantifying the coupled cycles of carbon and water is essential for exploring the response mechanisms of arid zone terrestrial ecosystems and for formulating a sustainable and practical solution to issues caused by climate change. Water use efficiency (WUE), one of the comprehensive indicators for assessing plant growth suitability, can accurately reflect vegetation’s dynamic response to changing climate patterns. This study assesses the spatio-temporal changes in WUE (ecosystem water use efficiency, soil water use efficiency, and precipitation water use efficiency) from 2000 to 2018 and quantifies their relationship with meteorological elements (precipitation, temperature, drought) and the vegetation index (NDVI). The study finds that the sensitivity of NDVI to WUE is highly consistent with the spatial law of precipitation. The εPre threshold range of different types of WUE is about 200 mm or 1600 mm (low-value valley point) and 300 mm or 1500 mm (high-value peak point), and the εTem threshold value is 3~6 °C (high-value peak point) and 9~12 °C (low-value valley point). The degree to which vegetation WUE is influenced by precipitation is positively correlated with its time lag, whereas the degree to which temperature influences vegetation is negatively correlated. The WUE time lag is very long in hilly regions and is less impacted by drought; it is quite short in plains and deserts, where it is substantially affected by drought. These findings may be of great significance in responding to the severe situation of increasingly scarce water resources and the deterioration of the ecological environment across Central Asia.

Quantifying the Spatio-Temporal Variations and Impacts of Factors on Vegetation Water Use Efficiency Using STL Decomposition and Geodetector Method

Water use efficiency of vegetation (WUE), the ratio of carbon gain to water loss, is a valid indicator to describe the photosynthetic carbon–water coupling relationship. Understanding how and why WUE changes are essential for regional ecological conservation. However, the impacts of various factors and their interactions on the spatial variation of WUE remain uncertain in the arid land of Northwest China. Here, we selected the Qilian Mountains (QM) and Hexi Corridor (HC) as the study areas. Supported by the Google Earth Engine, we explored the spatio-temporal variations of WUE in QM and HC for 2002–2021 using STL decomposition (a seasonal-trend decomposition procedure), trend analysis, and the Hurst index. Then, the Geodetector method was applied to quantify impacts of geographical and eco-meteorological factors on the spatial variation of WUE. The WUE in HC was higher than that in QM. Interestingly, the opposite longitude zonality characteristics are shown in the QM and HC. In QM, the WUE showed an upward trend with longitude increasing, while a downward trend with longitude increasing in the oases of HC. The WUE of cropland was the highest (1.15 ± 0.35 gC kg−1 H2O), and that of alpine vegetation was the lowest (0.2 ± 0.15 gC kg−1 H2O). WUE showed a decreasing trend across the study area, almost certainly due to a drop from May to July during 2002–2021. The air temperature is the dominant factor influencing the spatial variation of WUE. In addition, the interaction of any two factors is greater than the independent influence of either factor alone. The Geodetector method proved to be effective for quantifying the impact of complex multi-factors on the spatial variation of WUE. This study provides a new technical scheme to analyze the spatio-temporal pattern and quantify the impact of multi-factors on the spatial variation of WUE. These findings aid in understanding underlying mechanisms of WUE variation and thereby will be beneficial for clarifying the response of vegetation to climate change.

Characterization of water use efficiency changes in Tibetan Plateau grasslands based on eco-geographic zoning.

Water use efficiency (WUE) is an effective indicator to study the coupling of terrestrial carbon and water cycles. The Tibetan Plateau (TP) is the most important ecological security barrier in China, and it is important to understand the characteristics of WUE and the change mechanism to study the carbon and water cycles of plateau ecosystems and the rational use of water resources. This study analyzes the spatial and temporal characteristics of WUE on the TP and the influence of climate factors on WUE based on the gross primary productivity (GPP) and evapotranspiration (ET) data from GLASS. The results show that from 1985 to 2018, the WUE of the TP is on the rise under the combined effect of GPP and ET; the regions with higher mean WUE values are the southeastern and eastern parts of the plateau, and the low value areas are the central and northwestern parts of the plateau. Compared with precipitation, WUE is influenced by temperature over a larger area. The correlations between precipitation and temperature and WUE in different eco-geographic regions are complex, and there is a threshold effect on the correlation between WUE and temperature and precipitation. Temperature is the main driver of WUE changes in HIIA and HIB1 regions, while precipitation has a greater impact on WUE changes in HIIC2, HIIC2, HIC2, HIID3, and HIIC regions. Precipitation, temperature, and elevation are the main factors explaining the variation of WUE in the TP. According to the risk detector, it can be determined that grassland vegetation in warm and humid steep areas of low and medium elevations is more able to maintain efficient use of water. Meanwhile, grasslands located in the shade of northern slopes have weaker transpiration, which is conducive to vegetation accumulation of growth water, and thus can ensure higher WUE. The related study can provide a reference for the response of vegetation WUE to global changes in key climatic regions.

Improved Vegetation Ecological Quality of the Three-North Shelterbelt Project Region of China during 2000–2020 as Evidenced from Multiple Remotely Sensed Indicators

Evaluation of the long-term effect of ecosystem recovery projects is critical for future ecological management and sustainable development. The Three-North Shelterbelt (TNS) is a large-scale afforestation project in a crucial region of China. Numerous researchers have evaluated the vegetation ecological quality (VEQ) of the TNS using a single vegetation indicator. However, vegetation ecosystems are complex and need to be evaluated through various indicators. We constructed the vegetation ecological quality index (VEQI) by downscaling net primary productivity, leaf area index, fractional vegetation cover, land surface temperature, vegetation moisture, and water use efficiency of vegetation. The spatiotemporal characteristics and main contributing factors of VEQ in the TNS from 2000 to 2020 were investigated using SEN+Mann−Kendall, Hurst exponent, geographical detector, and residual trend analysis testing. The results suggest that VEQ in the TNS showed an improving trend over the 21-year study period. The areas with significant improvements were concentrated in the central and eastern parts of the TNS. Significant deterioration occurred only sporadically in various urban areas. Characteristics of future unsustainable VEQ trends could be detected across the TNS. Precipitation, vegetation type, soil type, elevation, and solar radiation exhibited the greatest impact on VEQ throughout the TNS. Human activities (e.g., afforestation and government investments) were the dominant factors and had a relative contribution of 65.24% to vegetation area change. Our results provide clues for assessing environmental recovery and sustainable development in other regions.

Variation Characteristics of Ecosystem Water Use Efficiency and Its Response to Human Activity and Climate Change in Inner Mongolia

Water use efficiency (WUE) reflects the balance between carbon assimilation and water consumption in terrestrial ecosystems. Considering the fragile conditions of global water resources, the evaluation of regional WUE variation characteristics and response mechanisms is critical for promoting sustainable ecological development and water resource utilization. Based on gross primary productivity (GPP) and evapotranspiration (ET) datasets, combined with vegetation and meteorological data, this study examined the spatiotemporal variations, annual variation contribution rate, and driving mechanism of WUE in Inner Mongolia from 2001 to 2020. The main results are as follows: (1) The interannual and spatial variations of GPP, ET, and WUE all exhibited increasing trends, with WUE increasing in approximately 70% of the region and significantly increasing in 22.35% of pixels exhibiting a significant increase. Areas with the most significant increases were located in the Horqin sandy land and Mu Us sandy land. (2) The highest WUE values were observed in the summer season, followed by autumn and winter, and the lowest in spring. (3) Among all vegetation types, the typical steppe ecosystems contributed most to the interannual variability (IAV) of GPP, ET, and WUE, with values of 169.89%, 141.09%, and 193.42%, respectively. While the coniferous forest contributed least or negatively to GPP, ET, and WUE IAV, with values of −36.28%, 28.20%, and −32.86%, respectively. (4) The primary driver of WUE variation was found to be GPP, which contributed 59.36%, mainly in the central and western regions. The remaining 40.64% was attributable to ET, concentrated in the northeast region. (5) Human activities significantly affected WUE, with a contribution (about 53.52%) larger than that of climate change (nearly 46.48%). Increased precipitation improves vegetation WUE and is the most important climate factor influencing WUE variations. These findings will aid the formulation of vegetation protection and water resource management strategies in water-stressed areas.

Biomass, Carbon and Nitrogen Partitioning and Water Use Efficiency Differences of Five Types of Alpine Grasslands in the Northern Tibetan Plateau.

(1) Background: Grassland covers most areas of the northern Tibetan Plateau along with important global terrestrial carbon (C) and nitrogen (N) pools, so there is a need to better understand the different alpine grassland growth associated with ecosystem C, N storage and water use efficiency (WUE). (2) Methods: The plant biomass and C, N concentrations, stocks and vegetation WUE of five kinds of alpine grassland types were investigated in northern Tibetan Plateau. (3) Results: The results showed that there were significant differences among five types of alpine grasslands in aboveground biomass (AGB), belowground biomass (BGB), total biomass (TB) and root:shoot (R/S) ratio while the highest value of different indices was shown in alpine meadow type (AM). The AGB and BGB partitioning results significantly satisfied the allometric biomass partitioning theory. The C, N concentrations and C/N of the vegetation in AGB and BGB showed significant grassland type differences. The highest C, N stocks of BGB were in AM which was almost six or seven times more than the C, N stocks of AGB in alpine desert type (AD). There were significant differences in δ13C and intrinsic water use efficiency (WUEi) under five alpine grassland types while the highest mean values of foliar δ13C and WUEi were in AD. Significant negative correlations were found between WUEi and C, N concentrations, C/N of AGB and soil water content (SWC) while the correlation with BGB C/N was not significant. For AGB, BGB, TB and R/S, there were positive correlations with C, N concentrations of AGB, BGB and SWC while it had significant negative correlations with C/N of BGB. (4) Conclusions: With regard to its types, it is suggested that the AM or AS may be an actively growing grassland type in the northern Tibetan Plateau.

Distribution and Driving Force of Water Use Efficiency under Vegetation Restoration on the Loess Plateau

The Grain for Green Project (GGP) has considerably improved the vegetation cover of the Loess Plateau, as well as changed the carbon and water coupling process of local vegetation to a certain extent. Water use efficiency (WUE) is a crucial measure for evaluating ecosystem responses to global climate change and is a key indicator of the carbon–water coupling between terrestrial ecosystems and the environment. A comprehensive understanding of the impact of vegetation reconstruction on WUE on the Loess Plateau is of great significance to the vegetation growth and contribution to sustainable of the Loess Plateau. In recent years, scholars have gained a more comprehensive understanding of the distribution and drivers of WUE on the Loess Plateau. However, through the study of carbon and water coupling in the Loess Plateau, it is found that the effects of different vegetation restoration levels on WUE are still to be studied in depth in terms of spatial and temporal heterogeneity and long timeseries. In this paper, we analyzed the trends of Normalized Difference vegetation cover (NDVI) and WUE from 2001 to 2010 and 2011 to 2020, respectively, to research at the WUE of the vegetation in this area in relation to vegetation restoration. It was found that the Loess Plateau’s vegetation WUE rose from 2001 to 2020 at a rate of 0.023 g C kg−1 H2O per year, and that the increase from 2011 to 2020 was more significant than the growth from 2000 to 2010. The Loess Plateau’s area with a growing trend in vegetation water use rate increased from 77.12% in 2001–2010 to 88.63% in 2011–2020, with the majority of the increased area occurring in the northeastern Inner Mongolia region. After 20 years of the reforestation project, the area where NDVI and WUE increased simultaneously accounted for 71.54% of the Loess Plateau, the area where NDVI increased but WUE decreased accounted for 10.95% of the Loess Plateau, and the area where NDVI increased but WUE decreased accounted for 7.15% of the Loess Plateau. The correlation between temperature precipitation and WUE was not significant for the whole Loess Plateau, further indicating that the increase in vegetation cover was the main reason for the increase in vegetation water efficiency. Therefore, the effect of vegetation cover on WUE should be fully considered when vegetation restoration is carried out on the Loess Plateau.

Responses of Water Use Efficiency to climate change in evapotranspiration and transpiration ecosystems

Climate change intensifies the fluctuation of arid/semi-arid evaporation and rearranges vegetation distribution patterns. Therefore, popular studies were proceeded, such as the responses of ecosystem’s water use efficiency(EWUE) and vegetation water use efficiency(VWUE) to precipitation and temperature fluctuations, which are essential to understand the relationship between carbon and water in ecosystems. Herein, this study defines two types of EWUE (GPP/ET; ET: evapotranspiration) and VWUE(GPP/T; T: transpiration to response to climate change, through which the spatial and temporal were revealed. We found that the decreasing rate of VWUE is greater than EWUE in winter (December). The interannual fluctuation(2000–2014 year) VWUE showed a decreasing trend (slope = -0.001). However, the EWUE showed an increasing trend (slope = 0.0014). There is a significant spatial pattern of differences between the stability of EWUE and VWUE. Precipitation negatively affects WUE (EWUE:79.4 %; VWUE:63.6 %), and temperature significantly affects WUE (EWUE:87.9 %; VWUE:87.7 %). The negative contribution of temperature and precipitation to VWUE is 81.73 % and 53.60 %, and the positive contribution is 12.27 % and 46.40 %, respectively. The negative contribution of temperature and precipitation to EWUE is 87.87 % and 66.55 %, and the positive contribution is 12.13 % and 33.45 %, respectively. The negative contribution rate indicates that climate factors have a promoting effect on WUE. The greater the negative contribution rate, the more pronounced the promoting effect. Through sensitivity and contribution rate methods analysis, the results of the two methods are consistent: precipitation attenuates WUE and temperature promotes WUE. This study enhanced our understanding of the climate response of ecosystems and vegetation canopy of carbon water fluxes.

Remote sensing of water use efficiency in Southwest China's karst area.

As the largest contiguous karst area in China, the southwestern karst area is a typical ecologically fragile area affecting local vegetation dynamics. Ecosystem water use efficiency (WUE) is an important factor reflecting the ability of vegetation to produce organic matter with a limited water supply. Therefore, determining the WUE variation trends in this ecologically fragile region is important. In this paper, we used MODIS remote sensing datasets, meteorological data, and land cover data to analyze the spatiotemporal changes in vegetation water use efficiency in the southwestern karst region from 2001 to 2017. We also further quantitatively analyzed the effects of climate change and human activities on the spatial and temporal patterns of vegetation WUE in the study area. The main conclusions were as follows. (1) From 2001 to 2017, in terms of temporal characteristics, the interannual variation in WUE fluctuated greatly, ranging from 1.33 to 1.51g C kg-1 H2O, with a multiyear average of 1.43g C kg-1 H2O and an average rate of change of - 0.0046g C kg-1 H2O year-1. In terms of spatial characteristics, areas with a higher WUE were concentrated in central Sichuan and northeastern Yunnan. (2) The annual average WUE of each vegetation type decreased in the following order: evergreen coniferous forest > evergreen broad-leaved forest > mixed forest > deciduous broad-leaved forest > cultivated land > deciduous coniferous forest > grassland > cultivated land and natural vegetation > shrub forest. (3) The vegetation WUE of 70.66% in this area was positively correlated with temperature. Additionally, 79.68% of the vegetation WUE was negatively correlated with precipitation. The relative contribution rates of climate change and human activities to the change trend in WUE were 15% and 85%, respectively. Compared with WUE results in other studies, the WUE of different karst landform areas obtained in this study was quite different, indicating that the geological and landform features of the karst area are complex. Our study provides scientific support for local vegetation restoration and protection policies and promotes the understanding of the principle of the carbon-water cycle in karst areas.

Vegetation in Arid Areas of the Loess Plateau Showed More Sensitivity of Water-Use Efficiency to Seasonal Drought

Studying the impact of regional or seasonal drought on vegetation water-use efficiency (WUE) can identify an effective theoretical basis by which vegetation can cope with future climate change. Based on remote sensing data and climate grid data, in this study, we calculated the ecosystem WUE and standardized precipitation evapotranspiration index (SPEI), analyzed the temporal and spatial divergence of seasonal drought and WUE, and explored the relationship between WUE and seasonal drought in the Loess Plateau. The results indicate that from 2001 to 2019, the humidity in spring and summer on the Loess Plateau shows an increasing trend, and the aridity in fall also shows an increasing trend. Averaged over four seasons, WUE presents distribution characteristics of “high in the southeast and low in the northwest”, with the highest WUE in summer. However, the geological distribution of the sensitivity of WUE to seasonal drought was significantly different. Spring drought increased WUE, whereas summer drought led to a decrease in WUE. When fall drought was less severe, the WUE increased; WUE response to winter SPEI was negative, but the sensitivity did not change with variation of drought degree. The sensitivity of WUE to the magnitude of seasonal drought was affected by regional dry and wet conditions. A clear seasonal divergence was found in four climate regions, along with increased drought intensity, and the sensitivity of WUE to drought magnitude in arid areas was generally higher than that in semi-arid, semi-humid areas, or humid areas. With this study, we deeply explored how ecosystems deal with the water supply strategy of seasonal drought, which is of great significance in the understanding of the coupling relationship between the carbon–water cycle and climate change.

云南省植被水分利用效率时空变化及影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 云南省植被水分利用效率时空变化及影响因素 DOI: 10.5846/stxb202011253023 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41871198） Spatiotemporal variation and influencing factors of vegetation water use efficiency in Yunnan Province Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:对云南省植被水分利用效率（WUE）的时空特征及影响因素进行研究可以更加全面的了解全球气候变化在区域上的响应。基于MODIS数据定量估算了2000-2014年云南省植被水分利用效率，利用趋势分析法和相关分析来对其时空格局和影响因素进行研究。研究结果表明：（1）云南省植被WUE整体呈现显著上升的趋势，增速为0.0078 gC mm-1 m-2 a-1，年内表现为"M"型的变化趋势。2009-2013年的干旱对该地区植被WUE产生了滞后的正效应。不同土地利用类型下的植被WUE从高到低依次为森林，灌木地，草地和耕地。（2）在空间分布上植被WUE呈现西部高于东部的分布特征；在时间尺度上呈现北增南减的趋势。云贵高原与青藏高原的连接区域--丽江市的植被WUE最高，整体上大于2.5 gC mm-1 m-2。澜沧江上游的三江并流区植被WUE随着山脉的走势呈现条状变化分布，不仅是植被WUE的低值集中区，同时也是植被WUE增加10%以上的集中区，另外滇东北和滇东南也是植被WUE的低值区。总的来看，除丽江以外，其他WUE高值区从2000-2014年呈下降的趋势，WUE低值区呈上升的趋势。（3）随着海拔的上升，植被WUE呈先上升后下降的变化趋势，并且海拔越高植被WUE增加越明显，变化率为0.01%。在低海拔区植被蒸散量（ET）和总初级生产力（GPP）都较高，随着海拔的上升ET骤降，GPP波动下降，直至海拔3000 m左右植被WUE达到峰值。高于海拔3000 m后，GPP直线下降，ET波动变化，直至海拔5000 m左右植被WUE几乎为0。（4）相较于降水因子，植被WUE受气温影响更大，特别是在三江并流区，其他地区则受非气候因素影响较大。在全球气候变化的背景下，这些发现展现了全球碳水循环变化在区域上的响应；云南省作为中国低纬高原的主体，研究也可为全球低纬高原区域生态建设提供参考。 Abstract:The study of the spatiotemporal characteristics and influencing factors of vegetation water use efficiency (WUE) in Yunnan Province could provide a more comprehensively understanding of the regional response to global climate change. In this study, MODIS data were used to quantitatively estimate the water use efficiency in Yunnan Province from 2000 to 2014, and trend analysis and correlation analysis were used to investigate the spatiotemporal patterns and influencing factors. The results showed that:(1) the overall WUE in Yunnan Province indicated a significant upward trend, with a growth rate of 0.0078 gC mm-1 m-2 a-1, and exhibited an "M" shape trend during the year. The drought events that occurred during 2009-2013 had a lagged positive effect on the vegetation WUE in this area. The vegetation WUEs of different land use types, in descending order, were forest, shrubland, grassland and the cultivated land. (2) The spatial distribution of WUE was higher in the west than in the east with a tendency of increasing in the north and decreasing in the south. The highest WUE was found in Lijiang, the region connecting the Yunnan-Guizhou Plateau and the Qinghai-Tibet Plateau, where the WUE was greater than 2.5 gC mm-1 m-2 overall. The vegetation WUE in the Three Parallel Rivers of upper Lancang River showed a striped distribution with the trend of the mountains, and was a concentration of low vegetation values. But it was also a focus where the WUE increased by more than 10%. In addition, northeastern and southeastern Yunnan were also areas with low WUE. Overall, except for Lijiang, there was a decreasing trend of high WUE and an increasing trend of low WUE from 2000 to 2014. (3) With the rise of altitude, WUE showed a tendency to increase first and then decrease, and the increase of WUE was more obvious in the higher altitude, with a change rate of 0.01%. Both evapotranspiration (ET) and Gross Primary Productivity (GPP) were prominent at low altitude, and with the rise of altitude ET plummets and GPP fluctuates and decreases until the peak of WUE was reached 3000 m. Above about 3000 m, the GPP dropped linearly and the ET fluctuated until the WUE was almost zero at about 5000 m. (4) Compared with precipitation, WUE was more obviously influenced by temperature, especially in the Three Parallel Rivers, while other regions were more significantly influenced by non-climatic factors. In the context of global climate change, the findings demonstrated the regional response to changes in the global carbon and water cycle; as the main body of low-latitude plateau in China, this study also could provide a reference for the ecological construction in low-latitude plateau regions around the world. 参考文献 相似文献 引证文献

The seasonal response of vegetation water use efficiency to temperature and precipitation in the Loess Plateau, China

Water use efficiency (WUE), which integrates ecosystem carbon and water cycles, is an important index for evaluating ecosystem sensitivity to climate change. Based on MODIS remote sensing data and meteorological data, this paper quantitatively studied the variation in seasonal vegetation WUE in the Loess Plateau over the period 2001–2019. Temperature and precipitation threshold effects on seasonal WUE of different vegetation types were also discovered using regression and partial correlation analysis methods. The results showed that seasonal WUE decreased with time in each season studied, with the rate of decrease of WUE in summer being the most significant of the three seasons studied. The following was the order of change in vegetation WUE values over time in different seasons: summer > autumn > spring. WUE of different vegetation types showed seasonal differences as well as varying responses to temperature and precipitation. The WUE of shrubland and grassland both tended to decrease over the study period from spring to autumn, with grassland WUE decreasing the most. When compared to grassland and shrubland, the negative relationship between forest WUE and the temperature was highest in spring and summer. The proportion of the area of vegetation where WUE was negatively correlated with temperature and precipitation in the three seasons, was largest in summer. In the relationship between seasonal WUE and either temperature or precipitation, there was a threshold effect. In spring, summer, and autumn, the optimum precipitation thresholds were 50–80 mm, 280–370 mm, and 65–125 mm, respectively, and the corresponding optimum temperature thresholds were > 14 °C, 15–19 °C, and 6–13 °C, respectively.