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Zhang Y.-Z.,Beijing Normal University | Zhang Y.-Z.,Institute of Urban Meteorology | Miao S.-G.,Institute of Urban Meteorology | Dai Y.-J.,Beijing Normal University | Liu Y.-H.,Beijing Municipal Climate Center
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2013

Weather Research and Forecasting (WRF) modeling system coupled with Noah land surface model and single layer urban canopy model was improved and optimized. Performances of the modeling system before and after optmization were examined, and diurnal variation of features of urban boundary layer was analyzed, through the numerical study of clear day during 6th and 7th Aug, 2010 over Beijing area. Furthermore, the impacts of urban underlying surface in Beijing and Tianjin on sea breeze were studied through two groups of model sensitivity tests using optimized modeling system. The results show that the optimization can evidently improve the performance of modeling system in the case study in the article. The modeling system can simulate the features of diurnal variation of summer boundary layer in Beijing generally well. Accurate geography data, such as land use and land cover classification information, play a very important role in improving the accuracy of model results. Beijing city and Tianjin city have obvious impacts on the evolution of sea breeze. As the sea breeze penetrating inland, the cities can pose an obstacle to the landward advance of sea breeze current, strengthen the horizontal convergence of wind and vertical updraft. The urban underlying surface in Beijing can also produce faster penetration with stronger intensity of sea breeze before it reaching the city, and increase the lifecycle and inland penetration distance of sea breeze after it passing over the city.

Xing P.,Tsinghua University | Xing P.,Beijing Municipal Climate Center | Chen X.,Tsinghua University | Chen X.,Joint Center for Global Change Studies | And 8 more authors.
PLoS ONE | Year: 2016

Large-scale climate history of the past millennium reconstructed solely from tree-ring data is prone to underestimate the amplitude of low-frequency variability. In this paper, we aimed at solving this problem by utilizing a novel method termed "MDVM", which was a combination of the ensemble empirical mode decomposition (EEMD) and variance matching techniques. We compiled a set of 211 tree-ring records from the extratropical Northern Hemisphere (30-90°N) in an effort to develop a new reconstruction of the annual mean temperature by the MDVM method. Among these dataset, a number of 126 records were screened out to reconstruct temperature variability longer than decadal scale for the period 850-2000 AD. The MDVM reconstruction depicted significant low-frequency variability in the past millennium with evident Medieval Warm Period (MWP) over the interval 950-1150 AD and pronounced Little Ice Age (LIA) cumulating in 1450-1850 AD. In the context of 1150-year reconstruction, the accelerating warming in 20th century was likely unprecedented, and the coldest decades appeared in the 1640s, 1600s and 1580s, whereas the warmest decades occurred in the 1990s, 1940s and 1930s. Additionally, the MDVM reconstruction covaried broadly with changes in natural radiative forcing, and especially showed distinct footprints of multiple volcanic eruptions in the last millennium. Comparisons of our results with previous reconstructions and model simulations showed the efficiency of the MDVM method on capturing low-frequency variability, particularly much colder signals of the LIA relative to the reference period. Our results demonstrated that the MDVM method has advantages in studying large-scale and low-frequency climate signals using pure tree-ring data. © 2016 Xing et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Liu Y.,Beijing Municipal Climate Center | Fang X.,Beijing Municipal Climate Center | Cheng C.,Beijing Municipal Climate Center | Luan Q.,Beijing Municipal Climate Center | And 3 more authors.
Meteorological Applications | Year: 2016

A method of performing city-scale ventilation assessments based on remote sensing (RS) and geographic information system (GIS) technology is proposed and applied effectively in an assessment of the local ventilation environment before and after the construction of the Yanqi Lake Eco-city in Huairou District, Beijing. The ventilation environment of a city is dependent on its background wind environment and ventilation potential. The background wind environment can be assessed through meteorological statistical analyses or numerical simulations, whereas the ventilation potential can be estimated using the underlying surface dynamic roughness length (RL) and the surrounding sky view factor (SVF). Based on the principle of morphology, the RL of a vegetation area is determined mainly by the vegetation types, vegetation canopy area index and vegetation height, whereas the RL of an urban area is defined mainly by the building area coverage and building height. The SVF can be estimated according to high-resolution digital raster elevation data. Based on the combination of the RL and SVF, the ventilation potential is graded, and the ventilation potential index (VPI) is defined and used to assess quantitatively the ventilation capacity of the city. The present study calculates the RL of the Yanqi Lake Eco-city using Landsat-TM5 satellite data from 26 July 2011, Geoscience Laser Altimeter System (GLAS) satellite data from 2005 and Beijing basic geographical data at 1:2000 from 2009. Subsequently, the RL and ventilation potential distribution of the Yanqi Lake Eco-city is mapped at a 100m spatial resolution. The ventilation conditions before and after the construction of the Yanqi Lake Eco-city are evaluated using the VPI in combination with the background wind field. According to changes in the ventilation capacity, relevant policy suggestions for urban buildings and design factors for ventilated corridors are postulated. © 2016 Royal Meteorological Society.

Xu Y.,Nanjing University of Information Science and Technology | Xu Y.,Beijing Institute of Urban Meteorology | Liu Y.,Beijing Municipal Climate Center
Geographical Research | Year: 2015

Urban heat island (UHI) effect is an important impact factor of the regional climate and ecological environment. How to observe and analyse the spatial distribution of UHI has become an important issue of urban environmental research. In this paper, the near-surface air temperature of Beijing was derived based on the Landsat/TM satellite imagery on 26 July 2011 to study the near-surface UHI. A statistical model at 195-m window size was established to estimate the air temperature, using land surface temperature, normalized difference vegetation index, altitude, and surface albedo as independent variables. The mean absolute error (MAE) of the model was 0.87°C, and the R2 was 0.66, indicating that the method can be used to effectively estimate the air temperature. The air temperature distribution obtained from remote sensing revealed that the UHI effect in Beijing was very significant and showed a concentrated pattern. The heat island intensity was stronger in the southern part than in the northern part of the city. In addition, the relationship between the air temperature and impervious surfaces was analysed. The air temperature increased with increasing impervious surface coverage, and the rate of change depended on the impervious surface coverage. When the impervious surface coverage was below 40 per cent, the temperature increased rapidly with increasing impervious surface coverage, and when the impervious surface coverage was above 40 per cent, the temperature increased slowly. This study provides a new approach to monitor near-surface UHI and reveals its relationship with impervious surface, providing a scientific reference for urban planning and environmental assessment. © 2014 Institute of Australian Geographers.

Luan Q.,Beijing Municipal Climate Center | Ye C.,Beijing Municipal Climate Center | Li W.,Changping Meteorological Bureau
International Conference on Geoinformatics | Year: 2013

Vegetation coverage change to the northwest of Beijing, which is upper drift zone, has an important influence on Beijing's atmosphere environment and climate, while series of problems were caused by land-use change in this area. Therefore, we selected typical temporal remote sensing images in 1987, 1997, and 2008, which can represent climate's feature in that decades, to retrieve vegetation coverage of land and chose landscape indexes to analyze spatio-temporal change characteristics of vegetation landscape in northwest of Beijing. Our result indicated that the least vegetation areas and the highest discrete index value with major high fractional vegetation cover type is in 1980s, while the largest vegetation areas and the lowest discrete index value with major high and middle fractional vegetation cover type is in 1990s. Furthermore, comparably, vegetation area in 2000s is much less than in 1990s. Although discrete index fluctuates in different decades, absolute value varies only a small extent, which may indicated that high fractional vegetation cover type prevails in northwest of Beijing, or middle fractional vegetation cover type connects mostly, and vegetation coverage patches aggregate in high degree, which demonstrated local nature environment differ not too much and ecosystem is relative stable. © 2013 IEEE.

Li Q.,China Agricultural University | Li Q.,Beijing Municipal Climate Center | Xu L.,China Agricultural University | Pan X.,China Agricultural University | And 5 more authors.
Environmental Research Letters | Year: 2016

Plant phenology is an important indicator of ecosystem dynamics and services. However, little is understood of its responses to climate change, particularly in ecologically sensitive regions such as arid and semi-arid grasslands. In this study, we analyzed a long-term climate and plant phenology dataset of thirteen grassland species in the Inner Mongolia of China, collected during 1981-2011 time period, to understand temporal patterns of plant phenology and then developed a simple chilling-adjusted physiological model to simulate phenological responses of each plant species to climate change. The results of regional climate analysis suggested that the minimum temperature was increasing at a greater rate than mean and maximum temperatures in the region and the climate variability had significant impacts on vegetation phenology. Chilling from an early stage in spring in general slowed down the phenological development in most plant species, although there were some inconsistencies among sites and years. Specifically, we found lower precipitation during green-up resulted in delayed flowering, which may attribute to plant self-adjustment strategy to respond changes in climate. These climate dependent phenologies were characterized by a simple physiological model. Scenario analysis suggested that by 2071-2100 significant shifts in plant phenology are expected in Inner Mongolia, including as much as 6-11 days earlier in green-up time and 8-11 days shorter in growing season due to earlier senescence. © 2016 IOP Publishing Ltd.

Li L.,Shenzhen National Climate Observatory | Fang X.,Beijing Municipal Climate Center | Zhang L.,Shenzhen National Climate Observatory
Huanjing Kexue Xuebao/Acta Scientiae Circumstantiae | Year: 2012

Based on the computational fluid dynamics (CFD) method, the influences of air temperature stratification and ground heating on the flow field and the diffusion process in street canyon are studied. Aiming at two kinds of street canyons with depth-width ratios of 0.5 and 1.0, respectively, 18 numerical sensitivity tests are performed. The results of the numerical tests show that the ground heating plays a more important role than the air temperature stratification in the pollutant diffusion process in street canyon. The analysis shows that ground heating is able to remarkably promote the diffusion capability in the street canyon. When ground heating exists, the variations of the flow structure, the air exchange rate and the turbulence intensity generally tend to be favorable in removing the pollutant in the street canyon. Even under the condition of stable stratification, thermal circulation induced by ground heating is also able to transport and disperse the pollutant out of the street canyon, and consequently leads to the dropping of the pollutant concentration near ground.

Li L.,Shenzhen National Climate Observatory | Zhang L.-J.,Shenzhen National Climate Observatory | Zhang N.,Nanjing University | Hu F.,CAS Institute of Atmospheric Physics | And 3 more authors.
Wind and Structures, An International Journal | Year: 2010

A meteorological model, RAMS, and a commercial computational fluid dynamics (CFD) model, FLUENT are combined as a one-way off-line nested modeling system, namely, RAMS/FLUENT system. The system is experimentally applied in the wind simulation over a complex terrain, with which numerical simulations of wind field over Foyeding weather station located in the northwest mountainous area of Beijing metropolis are performed. The results show that the method of combining a meteorological model and a CFD model as a modeling system is reasonable. In RAMS/FLUENT system, more realistic boundary conditions are provided for FLUENT rather than idealized vertical wind profiles, and the finite volume method (FVM) of FLUENT ensures the capability of the modeling system on describing complex terrain in the simulation. Thus, RAMS/FLUENT can provide fine-scale realistic wind data over complex terrains.

Luan Q.,Beijing Municipal Climate Center | Fang X.,Beijing Municipal Climate Center | Ye C.,Beijing Municipal Climate Center | Liu Y.,Beijing Municipal Climate Center
International Conference on Geoinformatics | Year: 2016

In order to improve efficiency of defending agricultural drought and resolve the problem that kinds of service software are distributed and isolated, we designed and developed a synthetic system that integrated drought monitoring and forecasting and irrigation amount forecasting into a platform based on technology of the internet of things, hybrid programming and parallel computing. This system has three advantages. First, we improved algorithms of drought monitoring and forecasting so that products made by this system have a higher accuracy. Second, we designed a function called one-click-complete that needs only one click and can complete all business through one batch process, which could enhance efficiency for emergency handling. Third, we optimized the feature of high cohesion and low coupling from the view of business information flow and technology architecture, which could ensure stability. Now this system has been applied in most provinces in northern China and shows an excellent prospect for integrated service of drought monitoring and forecasting and irrigation amount forecasting. © 2015 IEEE.

Luan Q.,Beijing Municipal Climate Center | Ye C.,Beijing Municipal Climate Center | Liu Y.,Beijing Municipal Climate Center | Li S.,Beijing Municipal Climate Center
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2014

We analyzed dominant landscape feature parameter of Urban Green Land (UGL) that impact thermal environment of buildings, and researched the spatial distance that UGL could affect surrounding thermal environment and correlation between landscape coefficients of UGL and cooling range caused by UGL. In the scale of 100m spatial resolution, most UGL patches have a role in cooling effect on their surrounding buildings within 100m range. All UGL patches over 0.5 km2 could exert significant cooling effect on surrounding buildings within 100m, with temperature difference ranging from 0.46°C to 0.83°C, averaged at 0.72°C, while UGL patches below 0.5 km2 with high vegetation cover could play a cooling role, but nonsignificant cooling effect with low vegetation coverage. In addition, UGL patches' perimeter, area, shape index and vegetation coverage have no significant correlation with cooling range of their surrounding buildings. © 2014 Springer International Publishing.

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