Recently, whether drylands of Northwest China(NW) have become wetting has been attracting surging attentions. By comparing the Standard Precipitation Evapotranspiration Indices(SPEI) derived from two different potenti...Recently, whether drylands of Northwest China(NW) have become wetting has been attracting surging attentions. By comparing the Standard Precipitation Evapotranspiration Indices(SPEI) derived from two different potential evapotranspiration estimates, i.e., the Thornthwaite algorithm(SPEI_th) and the Penman-Monteith equation(SPEI_pm), we try to resolve the controversy. The analysis indicated that air temperature has been warming significantly at a rate of 0.4℃ decade^(-1) in the last five decades and the more arid areas are more prone to becoming warmer. Annual precipitation of the entire study area increased insignificantly by 3.6 mm decade^(-1) from 1970 to 2019 but NW presented significantly increasing trends. Further, the SPEI_th and SPEI_pm demonstrated similar wetting-drying-wetting trends(three phases) in China’s drylands during 1970–2019. The common periodical signals in the middle phase were identified both by SPEI_th and SPEI_pm wavelet analysis. Analysis with different temporal intervals can lead to divergent or even opposite results. The attribution analysis revealed that precipitation is the main climatic factor driving the drought trend transition. This study hints that the wetting trend’s direction and magnitude hinge on the targeted temporal periods and regions.展开更多
Relatively coordinated development among cities can typically promote the integration of the whole urban agglomeration,while urbanization of land has been found important to economic development in developing countrie...Relatively coordinated development among cities can typically promote the integration of the whole urban agglomeration,while urbanization of land has been found important to economic development in developing countries.Numerous studies have measured the urban land expansion in urban agglomerations.However,urban land spatial inequality under a specific spatial structure remains poorly understood.Here,we combined theβ-convergence model and the core-periphery structure to explore the dynamic changes in urban land spatial inequality in urban agglomerations.The Yangtze River Delta Urban Agglomeration(YRDUA)in China was selected as the study area.Indicators of urban land have been applied in conjunction with a modified conditionalβ-convergence model,while the existence of the core-periphery structure was tested by analyzing coefficients of the control variable.The results show that although the spatial inequality of urban land area had decreased during 2000–2020,the whole YRDUA had still shown an obvious core-periphery structure.Compared with urban land area,the spatial inequality of urban land economic density and population density had decreased more rapidly,and the core-periphery structure was less obvious.Our findings can help to improve our current understanding of urban agglomeration and serve as a scientific reference for the coordinated development of urban agglomerations.展开更多
Biologists have considered both winter coldness and temperature seasonality as major determinants of the northern limits of plants and animals in the Northern Hemisphere,which in turn drive the well-known latitudinal ...Biologists have considered both winter coldness and temperature seasonality as major determinants of the northern limits of plants and animals in the Northern Hemisphere,which in turn drive the well-known latitudinal diversity gradient.However,few studies have tested which of the two climate variables is the primary determinant.In this study,we assess whether winter coldness or temperature seasonality is more strongly associated with the northern latitudinal limits of tree species and with tree species richness in North America.Tree species were recorded in each of 1198 quadrats of 110 km×110 km in North America.We used correlation and regression analyses to assess the relationship of the latitude of the northern boundary of each species,and of species richness per quadrat,with winter coldness and temperature seasonality.Species richness was analyzed within 38 longitudinal,i.e.,north-south,bands(each being>1100 km long and 110 km wide).The latitudes of the northern range limits of tree species were three times better correlated with minimum temperatures at those latitudes than with temperature seasonality.On average,minimum temperature and temperature seasonality together explained 81.5%of the variation in the northern range limits of the tree species examined,and minimum temperature uniquely explained six-fold(33.7%versus 5.8%)more of this variation than did temperature seasonality.Correlations of tree species richness with minimum temperatures were stronger than correlations with temperature seasonality for most of the longitudinal bands analyzed.Compared to temperature seasonality,winter coldness is more strongly associated with species distributions at high latitudes,and is likely a more important driver of the latitudinal diversity gradient.展开更多
Understanding climatic effects on cropland water use efficiency at different elevations is imperative for managing agricultural water and production in response to ongoing climate change in climate-sensitive areas wit...Understanding climatic effects on cropland water use efficiency at different elevations is imperative for managing agricultural water and production in response to ongoing climate change in climate-sensitive areas with complex topography, such as southwestern China. We investigated climatic effects on cropland water use efficiency in southwestern China at each 100-m elevation bin during 2001–2017. The maximum water use efficiency was 1.71 gC kg^(–1) H_2O for the 1900–1999 m elevation bin under the growing season temperature and precipitation of 14.58±0.32℃ and 965.40±136.45 mm, respectively. The water use efficiency slopes were dominated by the evapotranspiration slopes at elevations below 1999 m but were controlled by the gross primary productivity slopes at elevations above 2000 m. This difference was caused by the substantial responses of evaporation to climate change at lower elevations and the increased climatic sensitivity of gross primary productivity at higher elevations. In comparison to those at other elevations, croplands at lower elevations were more vulnerable to extreme drought because of the dominant role fluctuating evapotranspiration played in water use efficiency. The findings will improve cropland water management in the study area.展开更多
基金The Major Program of National Natural Science Foundation of China,No.41991234The National Science Fund for Distinguished Young Scholars,No.41725003。
文摘Recently, whether drylands of Northwest China(NW) have become wetting has been attracting surging attentions. By comparing the Standard Precipitation Evapotranspiration Indices(SPEI) derived from two different potential evapotranspiration estimates, i.e., the Thornthwaite algorithm(SPEI_th) and the Penman-Monteith equation(SPEI_pm), we try to resolve the controversy. The analysis indicated that air temperature has been warming significantly at a rate of 0.4℃ decade^(-1) in the last five decades and the more arid areas are more prone to becoming warmer. Annual precipitation of the entire study area increased insignificantly by 3.6 mm decade^(-1) from 1970 to 2019 but NW presented significantly increasing trends. Further, the SPEI_th and SPEI_pm demonstrated similar wetting-drying-wetting trends(three phases) in China’s drylands during 1970–2019. The common periodical signals in the middle phase were identified both by SPEI_th and SPEI_pm wavelet analysis. Analysis with different temporal intervals can lead to divergent or even opposite results. The attribution analysis revealed that precipitation is the main climatic factor driving the drought trend transition. This study hints that the wetting trend’s direction and magnitude hinge on the targeted temporal periods and regions.
基金National Social Science Fund of China,No.20AGL025。
文摘Relatively coordinated development among cities can typically promote the integration of the whole urban agglomeration,while urbanization of land has been found important to economic development in developing countries.Numerous studies have measured the urban land expansion in urban agglomerations.However,urban land spatial inequality under a specific spatial structure remains poorly understood.Here,we combined theβ-convergence model and the core-periphery structure to explore the dynamic changes in urban land spatial inequality in urban agglomerations.The Yangtze River Delta Urban Agglomeration(YRDUA)in China was selected as the study area.Indicators of urban land have been applied in conjunction with a modified conditionalβ-convergence model,while the existence of the core-periphery structure was tested by analyzing coefficients of the control variable.The results show that although the spatial inequality of urban land area had decreased during 2000–2020,the whole YRDUA had still shown an obvious core-periphery structure.Compared with urban land area,the spatial inequality of urban land economic density and population density had decreased more rapidly,and the core-periphery structure was less obvious.Our findings can help to improve our current understanding of urban agglomeration and serve as a scientific reference for the coordinated development of urban agglomerations.
基金The Youth Innovation Promotion Association of Chinese Academy of Sciences (2020054)Bingwei Outstanding Young Talents Program of Institute of Geographic Sciences and Natural Resources Research,Chinese Academy of Sciences (2018RC202)+3 种基金The National Key Research Projects of China (2016YFC0502005,2017YFA0604801)The Second Comprehensive Scientific Investigation of the Tibetan Plateau (2019QZKK0302)The National Natural Science Foundation of China (31600432)Tibet Science and Technology Major Projects of the Pratacultural Industry (XZ201901NA03)。
基金National Key Technology Research and Development Program of China(2016YFC0501802,2017YFA0604802)National Natural Science Foundation of China(41571195,41501103)Youth Innovation Team Project of Key Laboratory of Ecosystem Network Observation and Modeling(LENOM2016Q0002)
基金supported by a grant form the National Key Research and Development Program,No.2019YFA0607302。
文摘Biologists have considered both winter coldness and temperature seasonality as major determinants of the northern limits of plants and animals in the Northern Hemisphere,which in turn drive the well-known latitudinal diversity gradient.However,few studies have tested which of the two climate variables is the primary determinant.In this study,we assess whether winter coldness or temperature seasonality is more strongly associated with the northern latitudinal limits of tree species and with tree species richness in North America.Tree species were recorded in each of 1198 quadrats of 110 km×110 km in North America.We used correlation and regression analyses to assess the relationship of the latitude of the northern boundary of each species,and of species richness per quadrat,with winter coldness and temperature seasonality.Species richness was analyzed within 38 longitudinal,i.e.,north-south,bands(each being>1100 km long and 110 km wide).The latitudes of the northern range limits of tree species were three times better correlated with minimum temperatures at those latitudes than with temperature seasonality.On average,minimum temperature and temperature seasonality together explained 81.5%of the variation in the northern range limits of the tree species examined,and minimum temperature uniquely explained six-fold(33.7%versus 5.8%)more of this variation than did temperature seasonality.Correlations of tree species richness with minimum temperatures were stronger than correlations with temperature seasonality for most of the longitudinal bands analyzed.Compared to temperature seasonality,winter coldness is more strongly associated with species distributions at high latitudes,and is likely a more important driver of the latitudinal diversity gradient.
基金National Natural Science Foundation of China,No.41501054Scientific Research Foundation of Shandong Technology and Business University,No.BS201735Key Research Program of Frontier Sciences of the Chinese Academy of Sciences,No.QYZDB-SSW-DQC005。
文摘Understanding climatic effects on cropland water use efficiency at different elevations is imperative for managing agricultural water and production in response to ongoing climate change in climate-sensitive areas with complex topography, such as southwestern China. We investigated climatic effects on cropland water use efficiency in southwestern China at each 100-m elevation bin during 2001–2017. The maximum water use efficiency was 1.71 gC kg^(–1) H_2O for the 1900–1999 m elevation bin under the growing season temperature and precipitation of 14.58±0.32℃ and 965.40±136.45 mm, respectively. The water use efficiency slopes were dominated by the evapotranspiration slopes at elevations below 1999 m but were controlled by the gross primary productivity slopes at elevations above 2000 m. This difference was caused by the substantial responses of evaporation to climate change at lower elevations and the increased climatic sensitivity of gross primary productivity at higher elevations. In comparison to those at other elevations, croplands at lower elevations were more vulnerable to extreme drought because of the dominant role fluctuating evapotranspiration played in water use efficiency. The findings will improve cropland water management in the study area.
