Since the implementation of the reform and opening up policy in China in the late 1970s, some meteorological stations ＇entered＇ cities passively due to urban expansion. Changes in the surface and built environment a...Since the implementation of the reform and opening up policy in China in the late 1970s, some meteorological stations ＇entered＇ cities passively due to urban expansion. Changes in the surface and built environment around the stations have influenced observa- tions of air temperature. When the observational data from urban stations are applied in the interpolation of national or regional scale air temperature dataset, they could lead to overes- timation of regional air temperature and inaccurate assessment of warming. In this study, the underlying surface surrounding 756 meteorological stations across China was identified based on remote sensing images over a number of time intervals to distinguish the rural sta- tions that ＇entered＇ into cities. Then, after removing the observational data from these stations which have been influenced by urban expansion, a dataset of background air temperatures was generated by interpolating the observational data from the remaining rural stations. The mean urban heat island effect intensity since 1970 was estimated by comparing the original observational records from urban stations with the background air temperature interpolated. The result shows that urban heat island effect does occur due to urban expansion, with a higher intensity in winter than in other seasons. Then the overestimation of regional air tem- perature is evaluated by comparing the two kinds of grid datasets of air temperature which are respectively interpolated by all stations＇ and rural stations＇ observational data. Spatially, the overestimation is relatively higher in eastern China than in the central part of China; however, both areas exhibit a much higher effect than is observed in western China. We concluded that in the last 40 years the mean temperature in China increased by about 1.58℃, of which about 0.01℃ was attributed to urban expansion, with a contribution of up to 0.09℃ in the core areas from the overestimation of air temperature.展开更多
Analysis of hourly underground temperature measurements at a medium-size (by population) US city as a function of depth and extending over 5+ years revealed a positive trend exceeding the rate of regional and global w...Analysis of hourly underground temperature measurements at a medium-size (by population) US city as a function of depth and extending over 5+ years revealed a positive trend exceeding the rate of regional and global warming by an order of magnitude. Measurements at depths greater than ~2 m are unaffected by daily fluctuations and sense only seasonal variability. A comparable trend also emerged from the surface temperature record of the largest US city (New York). Power spectral analysis of deep and shallow subsurface temperature records showed respectively two kinds of power-law behavior: 1) a quasi-continuum of power amplitudes indicative of Brownian noise, superposed (in the shallow record) by 2) a discrete spectrum of diurnal harmonics attributable to the unequal heat flux between daylight and darkness. Spectral amplitudes of the deepest temperature time series (2.4 m) conformed to a log-hyperbolic distribution. Upon removal of seasonal variability from the temperature record, the resulting spectral amplitudes followed a log-exponential distribution. Dynamical analysis showed that relative amplitudes and phases of temperature records at different depths were in excellent accord with a 1-dimensional heat diffusion model.展开更多
[Objective] The aim was to study the characteristics of the changes of the urban boundary layer thermodynamic stability induced by heat island effect and their influences on precipitation.[Method] Proceeding from the ...[Objective] The aim was to study the characteristics of the changes of the urban boundary layer thermodynamic stability induced by heat island effect and their influences on precipitation.[Method] Proceeding from the thermodynamic equation,the changes of urban boundary layer thermodynamic stability caused by the urban heat disturbance and the mean state of heat island effect were discussed.The influence of the changes of urban boundary layer thermodynamic stability on the precipitation was expounded.Combining with case study of precipitation in Xi’an,the test was verified.[Result] Under interaction between the disturbed temperature and disturbed airflow,the boundary thermal disturbed stability(θ’z) was positive in the urban zone,as well as in the upstream and downstream areas of the city.But the stability in the urban zone was weaker than the suburbs,which favored for the short-time convective precipitation.For the boundary layer mean thermal stability(θ-0-0z) under the interaction between the mean airflow and mean environmental temperature,if the city zone was in the front of the warm ridge,the stability in the upstream of the city weakened which increased the instability of the boundary layer,while it increased in the downstream of the city.It was contrary if the city zone was in the font of the cold trough.For the mean airflow(prevailing wind) and the mean horizontal disturbed temperature,if it was upward motion in the boundary layer,the boundary layer mean thermal disturbed stability(θ’-0z) was negative in the downstream and positive in the upstream.Strong precipitation occured in the upstream of the city.It was contrary if it was descending air in the boundary layer.[Conclusion] The above results served some references for the fine city forecast.展开更多
In addition to landscape changes,urbanization also brings about changes in environmental factors that can affect wildlife.Despite the common referral in the published literature to multiple environmental factors such ...In addition to landscape changes,urbanization also brings about changes in environmental factors that can affect wildlife.Despite the common referral in the published literature to multiple environmental factors such as light and noise pollution,there is a gap in knowledge about their combined impact.We developed a multidimensional environmental framework to assess the effect of urbanization and multiple environmental factors(light,noise,and temperature)on life-history traits and breeding success of Barn Swallows(Hirundo rustica)across rural to urban gradients in four locations spanning over 2500 km from North to South China.Over a single breeding season,we measured these environmental factors nearby nests and quantified landscape urbanization over a 1km~2radius.We then analysed the relationships between these multiple environmental factors through a principal component analysis and conducted spatially explicit linear-mixed effects models to assess their effect on lifehistory traits and breeding success.We were particularly interested in understanding whether and how Barn Swallows were able to adapt to such environmental conditions associated with urbanization.The results show that there is significant variation in the exposure to environmental conditions experienced by Barn Swallows breeding across urbanization gradients in China.These changes and their effects are complex due to the behavioural responses ameliorating potential negative effects by selecting nesting sites that minimize exposure to environmental factors.However,significant relationships between landscape urbanization,exposure to environmental factors,and life-history traits such as laying date and clutch size were pervasive.Still,the impact on breeding success was,at least in our sample,negligible,suggesting that Barn Swallows are extremely adaptable to a wide range of environmental features.展开更多
基金National 973 Program of China, No.2010CB950900Swedish Research Links, No.2006-24724-44416-13
文摘Since the implementation of the reform and opening up policy in China in the late 1970s, some meteorological stations ＇entered＇ cities passively due to urban expansion. Changes in the surface and built environment around the stations have influenced observa- tions of air temperature. When the observational data from urban stations are applied in the interpolation of national or regional scale air temperature dataset, they could lead to overes- timation of regional air temperature and inaccurate assessment of warming. In this study, the underlying surface surrounding 756 meteorological stations across China was identified based on remote sensing images over a number of time intervals to distinguish the rural sta- tions that ＇entered＇ into cities. Then, after removing the observational data from these stations which have been influenced by urban expansion, a dataset of background air temperatures was generated by interpolating the observational data from the remaining rural stations. The mean urban heat island effect intensity since 1970 was estimated by comparing the original observational records from urban stations with the background air temperature interpolated. The result shows that urban heat island effect does occur due to urban expansion, with a higher intensity in winter than in other seasons. Then the overestimation of regional air tem- perature is evaluated by comparing the two kinds of grid datasets of air temperature which are respectively interpolated by all stations＇ and rural stations＇ observational data. Spatially, the overestimation is relatively higher in eastern China than in the central part of China; however, both areas exhibit a much higher effect than is observed in western China. We concluded that in the last 40 years the mean temperature in China increased by about 1.58℃, of which about 0.01℃ was attributed to urban expansion, with a contribution of up to 0.09℃ in the core areas from the overestimation of air temperature.
文摘Analysis of hourly underground temperature measurements at a medium-size (by population) US city as a function of depth and extending over 5+ years revealed a positive trend exceeding the rate of regional and global warming by an order of magnitude. Measurements at depths greater than ~2 m are unaffected by daily fluctuations and sense only seasonal variability. A comparable trend also emerged from the surface temperature record of the largest US city (New York). Power spectral analysis of deep and shallow subsurface temperature records showed respectively two kinds of power-law behavior: 1) a quasi-continuum of power amplitudes indicative of Brownian noise, superposed (in the shallow record) by 2) a discrete spectrum of diurnal harmonics attributable to the unequal heat flux between daylight and darkness. Spectral amplitudes of the deepest temperature time series (2.4 m) conformed to a log-hyperbolic distribution. Upon removal of seasonal variability from the temperature record, the resulting spectral amplitudes followed a log-exponential distribution. Dynamical analysis showed that relative amplitudes and phases of temperature records at different depths were in excellent accord with a 1-dimensional heat diffusion model.
基金Supported by Science and Technology Department Speciality Fund (GYHY200706004)National Science and Technology Support Planning Program (2007BAC29B03)
文摘[Objective] The aim was to study the characteristics of the changes of the urban boundary layer thermodynamic stability induced by heat island effect and their influences on precipitation.[Method] Proceeding from the thermodynamic equation,the changes of urban boundary layer thermodynamic stability caused by the urban heat disturbance and the mean state of heat island effect were discussed.The influence of the changes of urban boundary layer thermodynamic stability on the precipitation was expounded.Combining with case study of precipitation in Xi’an,the test was verified.[Result] Under interaction between the disturbed temperature and disturbed airflow,the boundary thermal disturbed stability(θ’z) was positive in the urban zone,as well as in the upstream and downstream areas of the city.But the stability in the urban zone was weaker than the suburbs,which favored for the short-time convective precipitation.For the boundary layer mean thermal stability(θ-0-0z) under the interaction between the mean airflow and mean environmental temperature,if the city zone was in the front of the warm ridge,the stability in the upstream of the city weakened which increased the instability of the boundary layer,while it increased in the downstream of the city.It was contrary if the city zone was in the font of the cold trough.For the mean airflow(prevailing wind) and the mean horizontal disturbed temperature,if it was upward motion in the boundary layer,the boundary layer mean thermal disturbed stability(θ’-0z) was negative in the downstream and positive in the upstream.Strong precipitation occured in the upstream of the city.It was contrary if it was descending air in the boundary layer.[Conclusion] The above results served some references for the fine city forecast.
基金funded by the National Natural Science Foundation of China(31770454 to E.P.N.,X.X.and R.J.S.)。
文摘In addition to landscape changes,urbanization also brings about changes in environmental factors that can affect wildlife.Despite the common referral in the published literature to multiple environmental factors such as light and noise pollution,there is a gap in knowledge about their combined impact.We developed a multidimensional environmental framework to assess the effect of urbanization and multiple environmental factors(light,noise,and temperature)on life-history traits and breeding success of Barn Swallows(Hirundo rustica)across rural to urban gradients in four locations spanning over 2500 km from North to South China.Over a single breeding season,we measured these environmental factors nearby nests and quantified landscape urbanization over a 1km~2radius.We then analysed the relationships between these multiple environmental factors through a principal component analysis and conducted spatially explicit linear-mixed effects models to assess their effect on lifehistory traits and breeding success.We were particularly interested in understanding whether and how Barn Swallows were able to adapt to such environmental conditions associated with urbanization.The results show that there is significant variation in the exposure to environmental conditions experienced by Barn Swallows breeding across urbanization gradients in China.These changes and their effects are complex due to the behavioural responses ameliorating potential negative effects by selecting nesting sites that minimize exposure to environmental factors.However,significant relationships between landscape urbanization,exposure to environmental factors,and life-history traits such as laying date and clutch size were pervasive.Still,the impact on breeding success was,at least in our sample,negligible,suggesting that Barn Swallows are extremely adaptable to a wide range of environmental features.
