Knowledge of both vegetation distribution pattern and phenology changes is very important.Their complicated relationship with elevation and accessibility were explored through a geographically weighted regression(GWR)...Knowledge of both vegetation distribution pattern and phenology changes is very important.Their complicated relationship with elevation and accessibility were explored through a geographically weighted regression(GWR) framework in Fujian province,China.The 16-day time series of 250 m Moderate Resolution Imaging Spectroradiometer(MODIS) Enhanced Vegetation Index(EVI) dataset from 2000 to 2010 was applied.Wavelet transform method was adopted to decompose the original time series and construct the annual maximum EVI and amplitude of the annual phenological cycle(EVI).Candidate explaining factors included topographic conditions,accessibility variables and proportions of primary vegetation types.Results revealed very strong positive influence from parameters of elevation and accessibility to big rivers and negative effect from accessibility to resident on both maximum EVI and phenological magnitude through ordinary linear least square(OLS) regression analysis.GWR analysis revealed that spatially,the parameters of topography and accessibility had a very complex relationship with both maximum EVI and phenology magnitude,as a result of the various combinations of environmental factors,vegetation composition and also intensive anthropogenic impact.Apart from the continuously increasing trend of phenology magnitude with increasing altitude,the influence of topography and accessibility on maximum EVI and phenological magnitude generally decreased,even from strongly positive to negative,with increasing altitude or distance.Specially,the most rapid change of correlation coefficient between them was observed within a low elevation or close distance;less variation was discovered within a certain range of medium altitude or distance and their relationship might change above this range.Non-stationary approaches are needed to better characterize the complex vegetation dynamic pattern in Mountain-hill Region.展开更多
This paper investigated spatiotemporal dynamic pattern of vegetation,climate factor,and their complex relationships from seasonal to inter-annual scale in China during the period 1982–1998 through wavelet transform m...This paper investigated spatiotemporal dynamic pattern of vegetation,climate factor,and their complex relationships from seasonal to inter-annual scale in China during the period 1982–1998 through wavelet transform method based on GIMMS data-sets.First,most vegetation canopies demonstrated obvious seasonality,increasing with latitudinal gradient.Second,obvious dynamic trends were observed in both vegetation and climate change,especially the positive trends.Over 70%areas were observed with obvious vegetation greening up,with vegetation degradation principally in the Pearl River Delta,Yangtze River Delta,and desert.Overall warming trend was observed across the whole country(>98%area),stronger in Northern China.Although over half of area(58.2%)obtained increasing rainfall trend,around a quarter of area(24.5%),especially the Central China and most northern portion of China,exhibited significantly negative rainfall trend.Third,significantly positive normalized difference vegetation index(NDVI)–climate relationship was generally observed on the de-noised time series in most vegetated regions,corresponding to their synchronous stronger seasonal pattern.Finally,at inter-annual level,the NDVI–climate relationship differed with climatic regions and their long-term trends:in humid regions,positive coefficients were observed except in regions with vegetation degradation;in arid,semiarid,and semihumid regions,positive relationships would be examined on the condition that increasing rainfall could compensate the increasing water requirement along with increasing temperature.This study provided valuable insights into the long-term vegetation–climate relationship in China with consideration of their spatiotemporal variability and overall trend in the global change process.展开更多
Most evaluation of the consistency of multisensor images have focused on Normalized Difference Vegetation Index （NDVI） products for natural landscapes, often neglecting less vegetated urban landscapes. This gap has ...Most evaluation of the consistency of multisensor images have focused on Normalized Difference Vegetation Index （NDVI） products for natural landscapes, often neglecting less vegetated urban landscapes. This gap has been filled through quantifying and evaluating spatial heterogeneity of urban and natural landscapes from QuickBird, Satellite pour l＇observation de la Terre （SPOT）, Ad- vanced Spacebome Thermal Emission and Reflection Radiometer （ASTER） and Landsat Thematic Mapper （TM） images with variogram analysis. Instead of a logarithmic relationship with pixel size observed in the corresponding aggregated images, the spatial variability decayed and the spatial structures decomposed more slowly and complexly with spatial resolution for real multisensor im- ages. As the spatial resolution increased, the proportion of spatial variability of the smaller spatial structure decreased quickly and only a larger spatial structure was observed at very coarse scales. Compared with visible band, greater spatial variability was observed in near infrared band for both densely and less densely vegetated landscapes. The influence of image size on spatial heterogeneity was highly dependent on whether the empirical sernivariogram reached its sill within the original image size. When the empirical semivariogram did not reach its sill at the original observation scale, spatial variability and mean characteristic length scale would increase with image size; otherwise they might decrease. This study could provide new insights into the knowledge of spatial heterogeneity in real multisen- sor images with consideration of their nominal spatial resolution, image size and spectral bands.展开更多
vegetation continuous The scale-location specific control on distribution was investigated through wavelet transforms approaches in subtropical mountain-hill region, Fujian, China. The Normalized Difference Vegetatio...vegetation continuous The scale-location specific control on distribution was investigated through wavelet transforms approaches in subtropical mountain-hill region, Fujian, China. The Normalized Difference Vegetation Index （NDVI） was calculated as an indicator of vegetation greenness using Chinese Environmental Disaster Reduction Satellite images along latitudinal and longitudinal transects. Four scales of variations were identified from the local wavelet spectrum of NDVI, with much stronger wavelet variances observed at larger scales. The characteristic scale of vegetation distribution within mountainous and hilly regions in Southeast China was around 20 km. Significantly strong wavelet coherency was generally examined in regions with very diverse topography, typically characterized as small mountains and hills fractured by rivers and residents. The continuous wavelet based approaches provided valuable insight on the hierarchical structure and its corresponding characteristic scales of ecosystems, which might be applied in defining proper levels in multilevel models and optimal bandwidths in Geographically Weighted Regression.展开更多
The complex spatiotemporal vegetation variability in the subtropical mountain-hill region was investigated through a multi-level modeling framework. Three levels - parcel, landscape, and river basin levels- were selec...The complex spatiotemporal vegetation variability in the subtropical mountain-hill region was investigated through a multi-level modeling framework. Three levels - parcel, landscape, and river basin levels- were selected to discover the complex spatiotemporal vegetation variability induced by climatic, geomorphic and anthropogenic processes at different levels. The wavelet transform method was adopted to construct the annual maximum Enhanced Vegetation Index and the amplitude of the annual phenological cycle based on the 16-day time series of a5om Moderate Resolution Imaging Spectroradiometer Enhanced Vegetation Index datasets during 2OOl-2OlO. Results revealed that land use strongly influenced the overall vegetation greenness and magnitude of phenological cycles. Topographic variables also contributed considerably to the models, reflecting the positive influence from altitude and slope. Additionally, climate factors played an important role： precipitation had a considerable positive association with the vegetation greenness, whereas the temperature difference had strong positive influence on the magnitude of vegetation phenology. The multilevel approach leads to a better understanding of the complex interaction of the hierarchical ecosystem, human activities and climate change.展开更多
Drought is widely known as an insidious hazard due to its complex and unique characteristics. Drought disasters have brought tremendous economic losses and significant social and environmental impacts to communities a...Drought is widely known as an insidious hazard due to its complex and unique characteristics. Drought disasters have brought tremendous economic losses and significant social and environmental impacts to communities across the globe. To further understand the hazard drought poses and provide insights into planning for drought preparedness, this article conducts a thorough literature review of drought hazard and drought planning frameworks within the United States. Two main approaches and three major forms of drought planning are discussed and summarized. Based on this review, a preliminary overview of drought planning status in the United States is presented. This study provides insight into major drought planning literature and establishes a link with drought mitigation and adaptation. The article concludes with discussion and implication for future drought planning and a future research outlook.展开更多
Understanding the seasonal behaviour of a subtropical forest and its inter-annual variation is crucial to understanding and monitoring its ecosystem function in the context of global warming. Based on the Moderate Res...Understanding the seasonal behaviour of a subtropical forest and its inter-annual variation is crucial to understanding and monitoring its ecosystem function in the context of global warming. Based on the Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index dataset, a wavelet transform method was used to investigate the inter-annual variations of vegetation phenology in a subtropical mountain and hill region in Fujian, China, during 2001-2010. The results show a distinct inter-annual variation of vegetation phenology related to climate variability even if most areas presented non-significant trends. The start dates significantly advanced and end dates delayed in 2003 and 2008, due to anomalously warm conditions. There was generally a gradient of increasing start dates, and earlier end dates of vegetation growing season, due to colder temperatures at higher altitudes. However, the altitudinal phenology relationship also depends on its corresponding rainfall conditions. Earlier start dates were observed at higher altitudes during rainfall deficit years such as 2008, which coincides with relatively abundant rainfall at higher altitudes. This paper reveals that vegetation phenology was coupled with altitudinal gradient, with distinct responses at different combinations of alternate temperature and precipitation conditions variability.展开更多
The U.S.federal government’s requirements and guidance for wetland conservation are reflected in a series of federal laws,regulations,and policies.However,the degree to which these requirements are reflected in local...The U.S.federal government’s requirements and guidance for wetland conservation are reflected in a series of federal laws,regulations,and policies.However,the degree to which these requirements are reflected in local planning efforts is unclear.This study using five components with 56 indicators evaluates how well wetland conservation efforts are integrated into 112 local comprehensive plans in Nebraska,USA.The results show that the majority of local comprehensive plans pay little direct attention to wetland conservation,although many conservation efforts are conducted under the umbrella of environmental protection frameworks.The indicators include water resource protection received the highest score and was the descriptor of natural or environmental resources and resulted in the highest level of local awareness on natural assets.The indicator of setting goals for no net loss of wetlands received the lowest score among all indicators,demonstrating a clear gap between the national vision and the local reality of wetland conservation.Findings suggest local governments need more direct and proactive inputs to improve wetland conservation.Further findings from this research provide a practical roadmap for planners globally,particularly for the developing countries,to integrate wetland conservation into the local planning systems.展开更多
A significant large number of dams have been constructed in the past two centuries in the United States. These dams＇ ability to regulate downstream flooding has received world-wide attention. In this study, data from...A significant large number of dams have been constructed in the past two centuries in the United States. These dams＇ ability to regulate downstream flooding has received world-wide attention. In this study, data from 38 rivers distributed over the entire conterminous Untied States with extensive pre- and post-dam annual peak discharge records, were collected to research the impacts of various dams on the flood behaviors at a national scale. The results indicate that dams have led to significant reductions in flood magnitude for nearly all of the sites; the decrease rate in the mean of annual peak discharge varies between 7.4% and 95.14%, except for the Dead River, which increased by 1.46%. Because of dams＇ effective- ness, the probability density curve of annual peak flow changes from a flat to peaked shape because both the range and magnitude of high discharges are decreased. More- over, the potential impact of dams on flood characteristics were closely related to the dam＇s geographic location and function, the ratio of the storage capacity of the dam to the mean annual runoff of the river （C/R）, and the ratio of reservoir storage capacity to the area of its drainage （C/D）. Specifically, the effects of dams on annual peak flows were more related to latitude than longitude. Compared with dams built for other purposes, the dam exclusively used for flood management cut off more flood peaks. Increases in the ratios of C/R and C/D increased the degree of modification of annual maximum discharge.展开更多
基金support forthis work from Chinese National Natural Science Foundation (Grant no. 41071267)Scientific Research Foundation for Returned Scholars,Ministry of Education of China ([2012]940)Science Foundation of Fujian province (Grant no.2012J01167,2012I0005)
文摘Knowledge of both vegetation distribution pattern and phenology changes is very important.Their complicated relationship with elevation and accessibility were explored through a geographically weighted regression(GWR) framework in Fujian province,China.The 16-day time series of 250 m Moderate Resolution Imaging Spectroradiometer(MODIS) Enhanced Vegetation Index(EVI) dataset from 2000 to 2010 was applied.Wavelet transform method was adopted to decompose the original time series and construct the annual maximum EVI and amplitude of the annual phenological cycle(EVI).Candidate explaining factors included topographic conditions,accessibility variables and proportions of primary vegetation types.Results revealed very strong positive influence from parameters of elevation and accessibility to big rivers and negative effect from accessibility to resident on both maximum EVI and phenological magnitude through ordinary linear least square(OLS) regression analysis.GWR analysis revealed that spatially,the parameters of topography and accessibility had a very complex relationship with both maximum EVI and phenology magnitude,as a result of the various combinations of environmental factors,vegetation composition and also intensive anthropogenic impact.Apart from the continuously increasing trend of phenology magnitude with increasing altitude,the influence of topography and accessibility on maximum EVI and phenological magnitude generally decreased,even from strongly positive to negative,with increasing altitude or distance.Specially,the most rapid change of correlation coefficient between them was observed within a low elevation or close distance;less variation was discovered within a certain range of medium altitude or distance and their relationship might change above this range.Non-stationary approaches are needed to better characterize the complex vegetation dynamic pattern in Mountain-hill Region.
基金The authors gratefully acknowledge the financial support received for this work from the National Natural Science Foundation of China(grant number 41071267)the Scientific Research Foundation for Returned Scholars,Ministry of Education of China(grant number[2012]940)the Science Foundation of Fujian Province(grant numbers 2012I0005 and 2012J01167)。
文摘This paper investigated spatiotemporal dynamic pattern of vegetation,climate factor,and their complex relationships from seasonal to inter-annual scale in China during the period 1982–1998 through wavelet transform method based on GIMMS data-sets.First,most vegetation canopies demonstrated obvious seasonality,increasing with latitudinal gradient.Second,obvious dynamic trends were observed in both vegetation and climate change,especially the positive trends.Over 70%areas were observed with obvious vegetation greening up,with vegetation degradation principally in the Pearl River Delta,Yangtze River Delta,and desert.Overall warming trend was observed across the whole country(>98%area),stronger in Northern China.Although over half of area(58.2%)obtained increasing rainfall trend,around a quarter of area(24.5%),especially the Central China and most northern portion of China,exhibited significantly negative rainfall trend.Third,significantly positive normalized difference vegetation index(NDVI)–climate relationship was generally observed on the de-noised time series in most vegetated regions,corresponding to their synchronous stronger seasonal pattern.Finally,at inter-annual level,the NDVI–climate relationship differed with climatic regions and their long-term trends:in humid regions,positive coefficients were observed except in regions with vegetation degradation;in arid,semiarid,and semihumid regions,positive relationships would be examined on the condition that increasing rainfall could compensate the increasing water requirement along with increasing temperature.This study provided valuable insights into the long-term vegetation–climate relationship in China with consideration of their spatiotemporal variability and overall trend in the global change process.
基金Under the auspices of National Natural Science Foundation of China(No.41071267,41001254)Natural Science Foundation of Fujian Province(No.2012I0005,2012J01167)
文摘Most evaluation of the consistency of multisensor images have focused on Normalized Difference Vegetation Index （NDVI） products for natural landscapes, often neglecting less vegetated urban landscapes. This gap has been filled through quantifying and evaluating spatial heterogeneity of urban and natural landscapes from QuickBird, Satellite pour l＇observation de la Terre （SPOT）, Ad- vanced Spacebome Thermal Emission and Reflection Radiometer （ASTER） and Landsat Thematic Mapper （TM） images with variogram analysis. Instead of a logarithmic relationship with pixel size observed in the corresponding aggregated images, the spatial variability decayed and the spatial structures decomposed more slowly and complexly with spatial resolution for real multisensor im- ages. As the spatial resolution increased, the proportion of spatial variability of the smaller spatial structure decreased quickly and only a larger spatial structure was observed at very coarse scales. Compared with visible band, greater spatial variability was observed in near infrared band for both densely and less densely vegetated landscapes. The influence of image size on spatial heterogeneity was highly dependent on whether the empirical sernivariogram reached its sill within the original image size. When the empirical semivariogram did not reach its sill at the original observation scale, spatial variability and mean characteristic length scale would increase with image size; otherwise they might decrease. This study could provide new insights into the knowledge of spatial heterogeneity in real multisen- sor images with consideration of their nominal spatial resolution, image size and spectral bands.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant No.41071267)Scientific Research Foundation for Returned Scholars,Ministry of Education of China(Grant No.[2012]940)the Science & Technology Department of Fujian Province,China(Grant Nos.2012I0005,2012J01167)
文摘vegetation continuous The scale-location specific control on distribution was investigated through wavelet transforms approaches in subtropical mountain-hill region, Fujian, China. The Normalized Difference Vegetation Index （NDVI） was calculated as an indicator of vegetation greenness using Chinese Environmental Disaster Reduction Satellite images along latitudinal and longitudinal transects. Four scales of variations were identified from the local wavelet spectrum of NDVI, with much stronger wavelet variances observed at larger scales. The characteristic scale of vegetation distribution within mountainous and hilly regions in Southeast China was around 20 km. Significantly strong wavelet coherency was generally examined in regions with very diverse topography, typically characterized as small mountains and hills fractured by rivers and residents. The continuous wavelet based approaches provided valuable insight on the hierarchical structure and its corresponding characteristic scales of ecosystems, which might be applied in defining proper levels in multilevel models and optimal bandwidths in Geographically Weighted Regression.
基金supported by the National Natural Science Foundation of China (NSFC) (Grant No. 41071267)Scientific Research Foundation for Returned Scholars ([2012]940)Ministry of Education of China, and the Science Foundation of Fujian Province (Grant Nos. 2012I0005, 2012J01167)
文摘The complex spatiotemporal vegetation variability in the subtropical mountain-hill region was investigated through a multi-level modeling framework. Three levels - parcel, landscape, and river basin levels- were selected to discover the complex spatiotemporal vegetation variability induced by climatic, geomorphic and anthropogenic processes at different levels. The wavelet transform method was adopted to construct the annual maximum Enhanced Vegetation Index and the amplitude of the annual phenological cycle based on the 16-day time series of a5om Moderate Resolution Imaging Spectroradiometer Enhanced Vegetation Index datasets during 2OOl-2OlO. Results revealed that land use strongly influenced the overall vegetation greenness and magnitude of phenological cycles. Topographic variables also contributed considerably to the models, reflecting the positive influence from altitude and slope. Additionally, climate factors played an important role： precipitation had a considerable positive association with the vegetation greenness, whereas the temperature difference had strong positive influence on the magnitude of vegetation phenology. The multilevel approach leads to a better understanding of the complex interaction of the hierarchical ecosystem, human activities and climate change.
文摘Drought is widely known as an insidious hazard due to its complex and unique characteristics. Drought disasters have brought tremendous economic losses and significant social and environmental impacts to communities across the globe. To further understand the hazard drought poses and provide insights into planning for drought preparedness, this article conducts a thorough literature review of drought hazard and drought planning frameworks within the United States. Two main approaches and three major forms of drought planning are discussed and summarized. Based on this review, a preliminary overview of drought planning status in the United States is presented. This study provides insight into major drought planning literature and establishes a link with drought mitigation and adaptation. The article concludes with discussion and implication for future drought planning and a future research outlook.
基金supported by the National Natural Science Foundation of China(41071267)the Scientific Research Foundation for Returned Scholars,Ministry of Education of China(2012940)Science Foundation of Fujian Province(2012J01167 and 2012I0005)
文摘Understanding the seasonal behaviour of a subtropical forest and its inter-annual variation is crucial to understanding and monitoring its ecosystem function in the context of global warming. Based on the Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index dataset, a wavelet transform method was used to investigate the inter-annual variations of vegetation phenology in a subtropical mountain and hill region in Fujian, China, during 2001-2010. The results show a distinct inter-annual variation of vegetation phenology related to climate variability even if most areas presented non-significant trends. The start dates significantly advanced and end dates delayed in 2003 and 2008, due to anomalously warm conditions. There was generally a gradient of increasing start dates, and earlier end dates of vegetation growing season, due to colder temperatures at higher altitudes. However, the altitudinal phenology relationship also depends on its corresponding rainfall conditions. Earlier start dates were observed at higher altitudes during rainfall deficit years such as 2008, which coincides with relatively abundant rainfall at higher altitudes. This paper reveals that vegetation phenology was coupled with altitudinal gradient, with distinct responses at different combinations of alternate temperature and precipitation conditions variability.
基金This work was supported by the U.S.Environmental Protection Agency[CD97790401]and[CD 97763501].
文摘The U.S.federal government’s requirements and guidance for wetland conservation are reflected in a series of federal laws,regulations,and policies.However,the degree to which these requirements are reflected in local planning efforts is unclear.This study using five components with 56 indicators evaluates how well wetland conservation efforts are integrated into 112 local comprehensive plans in Nebraska,USA.The results show that the majority of local comprehensive plans pay little direct attention to wetland conservation,although many conservation efforts are conducted under the umbrella of environmental protection frameworks.The indicators include water resource protection received the highest score and was the descriptor of natural or environmental resources and resulted in the highest level of local awareness on natural assets.The indicator of setting goals for no net loss of wetlands received the lowest score among all indicators,demonstrating a clear gap between the national vision and the local reality of wetland conservation.Findings suggest local governments need more direct and proactive inputs to improve wetland conservation.Further findings from this research provide a practical roadmap for planners globally,particularly for the developing countries,to integrate wetland conservation into the local planning systems.
文摘A significant large number of dams have been constructed in the past two centuries in the United States. These dams＇ ability to regulate downstream flooding has received world-wide attention. In this study, data from 38 rivers distributed over the entire conterminous Untied States with extensive pre- and post-dam annual peak discharge records, were collected to research the impacts of various dams on the flood behaviors at a national scale. The results indicate that dams have led to significant reductions in flood magnitude for nearly all of the sites; the decrease rate in the mean of annual peak discharge varies between 7.4% and 95.14%, except for the Dead River, which increased by 1.46%. Because of dams＇ effective- ness, the probability density curve of annual peak flow changes from a flat to peaked shape because both the range and magnitude of high discharges are decreased. More- over, the potential impact of dams on flood characteristics were closely related to the dam＇s geographic location and function, the ratio of the storage capacity of the dam to the mean annual runoff of the river （C/R）, and the ratio of reservoir storage capacity to the area of its drainage （C/D）. Specifically, the effects of dams on annual peak flows were more related to latitude than longitude. Compared with dams built for other purposes, the dam exclusively used for flood management cut off more flood peaks. Increases in the ratios of C/R and C/D increased the degree of modification of annual maximum discharge.
