Cold Island Effect Research Articles

Warm Island Effect in the Badain Jaran Desert Lake Group Region Inferred from the Accumulated Temperature

The Badain Jaran Desert (BJD) is characterized by the coexistence of over 110 perennial lakes and thousands of megadunes in its southeast part. Unlike the cold island effect, we found a special phenomenon of the warm island effect in the lake group region of the BJD. However, the concept and formation mechanism remains unclear. In this study, based on observations of land surface processes in the area, we first used the daily mean temperature from 23 automated meteorological stations from 2010 to 2017 to calculate the mean daily temperature (T) ≥ 0 °C, T ≥ 10 °C accumulated temperature and negative accumulated temperature. Furthermore, using the net radiation from two eddy covariance measurement systems, characteristics of the net radiation between the lake and megadunes were analyzed. When comparing observed data in the lake group region to surrounding areas, accumulated temperature from all three meteorological stations in the lake group region were higher; the duration days of T ≥ 0 °C and T ≥ 10 °C were longer, whereas duration days of negative accumulated temperature were shorter. In addition, the initial dates for T ≥ 0 °C and T ≥ 10 °C accumulated temperature were earlier, whereas the end dates were delayed. Variations in heat were observed between stations in the lake group region that may be reflective of microclimate environments between lakes. The authors relate warm island formation in the BJD lake group region to (1) the heat carried by groundwater recharge to the desert lake groups has a great impact on the local temperature. (2) Net heat radiation to the atmosphere through sensible heat flux owing to sparse vegetation in the desert areas. Hence, heat resources are richer in the lake group region. This study aims to improve our understanding of the warm island effect from a comprehensive analysis of its intensity and distribution pattern around the lake group region as compared to its surroundings. In addition, the results from this study will provide a scientific basis for determining the source of lake water in the BJD.

Influence of the low-level jet on the intensity of the nocturnal oasis cold island effect over northwest China

The nocturnal oasis cold island (OCI) effect is an important phenomenon seen over the heterogeneous surfaces of oases and deserts in northwest China and is influenced by many unknown complex factors. Using field observations and wind profile radar data over oases and deserts in Zhangye city, China, we analyze the relationship between the OCI effect and the low-level jet (LLJ). Vertical mixing induced by the LLJ has a profound impact on the intensity of the OCI effect during the night. The mean nocturnal intensity of the OCI effect and the strength of the nocturnal LLJ are significantly correlated. We investigate two examples in detail—one with a strong OCI effect and one with a weak OCI effect—using observational data and simulations by the Weather Research and Forecasting model. During a weak LLJ, when the wind speed decreases and vertical mixing is weakened, the increase in evaporation over the oasis causes the temperature to decrease dramatically and results in a strong OCI effect. During a strong LLJ, the strong shear induced below the nose of the LLJ enhances turbulent mixing, heat is transported downward, and the temperature over the oasis decreases slightly. The near-surface wind speed over the desert increases, and the decrease in temperature is larger than that during a weak LLJ. Therefore, the intensity of the OCI effect decreases during a strong LLJ.

Research on urban park design combined with the urban ventilation system

The disorderly construction of cities, the emissions of industrial gases and motor vehicle exhaust aggravate the environmental problems such as urban heat island and haze, thus imminent improvement of the urban thermal environment is required. Urban ventilation system can facilitate urban air circulation, which can alleviate the urban heat island effect and improve air quality to some extent. As an important part of the urban landscape system, the cool island effect of parks plays an important role in improving the urban thermal environment, combining the cold island effect of the park with the surrounding roads, building a small ventilation system in the area, which will help improve air quality in the region. This paper selects Chengdu Renmin Park as a case, and analysis the effects of different layout on the wind velocity by CFD method. The results show that (1) air passage disperses the air flow in the interior of the park; (2) but by air passage, the velocity at urban road where faced the air passage be improved in some degree; (3) moreover, the graphic and the length of the air passage has great effects on wind velocity.

Change Detection of Land Surface Temperature (LST) and some Related Parameters Using Landsat Image: a Case Study of the Ebinur Lake Watershed, Xinjiang, China

This study assesses and detects land use/cover (LUC) and land surface temperature (LST) change using multi-temporal Landsat TM satellite data. NDVI, albedo and MNDWI were used to analyze the LST qualitatively. The results revealed that the accuracy of LST measurements in watershed is within 1.5 °C. Then, temperature changes between 1998 and 2011 were analyzed. The classifications of land surface temperatures lie in five categories as follows: lower (1.9–8.9 °C), low (8.9–15.9 °C), middle (15.9–22.9 °C), high (22.9–29.9 °C), higher (29.9–36.9 °C), and highest (36.9–43.9 °C). Second, east-west profiles of the characteristics of the distribution of LUC types were made based on 1998 and 2011 images. By comparing LSTs in these two years, one can conclude woodland-grassland has a very strong influence on temperature. Third, LST increased with the increases in the density of salinized and desert lands, but decreased with the increase in vegetation cover. The relationship between MNDWI and LST was significantly negatively correlated. Multiple regression analyses between LST and each index as well as elevation were created to evaluate the watershed thermal environment. This regression showed that NDVI, albedo, MNDWI and a digital elevation model were effective indicators for quantifying the effects of land use/cover change (LUCC) on LST, and the correlation coefficient R was 0.806. Finally, natural and human factors were important factors affecting temperature change. Generally, the temperature of the oasis was lower than the surroundings, which results in a ‘cold island effect’.

人工输水对石羊河下游青土湖区域生态环境的影响分析

PDF HTML阅读 XML下载 导出引用 引用提醒 人工输水对石羊河下游青土湖区域生态环境的影响分析 DOI: 10.5846/stxb201701180154 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（31460134，31260129）；甘肃农业大学盛彤笙科技创新基金（GSAU-STS-1528） Influence analysis of artificial water transfer on the regional ecological environment of Qingtu Lake in the lower reaches of the Shiyang River 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:通过对石羊河下游青土湖人工输水后水面形成区环境要素变化的调查研究，分析了水面形成对区域地下水位、植被、大气温湿度、风速等的影响。结果表明：（1）由于输水方式、输水时间集中等因素影响，区域水面形成快速；且每个输水周期完成6个月后的区域保留水面积持续增大，4a间水面积增加4.52倍，面积扩大的叠加效应明显。（2）输水作用和水面的形成，促使输水区域地下水埋深由 > 6m，提升到0.6-3.2m。（3）水面形成促进了区域以白刺为代表的单一荒漠植被群落向芦苇草甸、盐化草甸等多样化群落演替。（4）水面形成的"冷岛效应"明显，促进了区域小气候环境的改善；输水区500m范围平均温度降低55.67%，湿度增加3倍。人工输水对青土湖区域生态环境的改善产生了明显的积极作用，但输水政策的持续性、输水策略调整等不确定性影响，以及水面形成对局部范围风沙活动、植物物种多样性等方面的负面影响值得关注和深入研究。 Abstract:This paper uses sample collection and position observation to survey and study changes of environmental elements in the aspect of 2010-2014 subterranean stage, vegetation, and narrow-scope climate of water-surface formation area for sake of making a quantitative assessment towards the effects of the regional ecological environment supplied water manually from Qingtu Lake off Shiyang River. In addition, the paper also analyzes the situation of water surface, depth of ground water at different time intervals, landscape structure of vegetation, species composition of vegetation community, and changes of quantity, air temperature, moisture, and wind speed. Some ecological factors were explored to respond to water surface formation. The findings show that (1) water surface becomes fast due to different delivery patterns and the duration of water delivery. Regional reserved water area increases to 6 months after each delivery, 4a water area increases by 4.52 times, the superimposed effect of area enlargement were apparent. (2) Water surface area increase and water delivery enlarges the regional ground water from 0.6 to 3.2m. The coefficient of association of reserved water area and ground water depth is 0.909. (3) The structure of original typical desert vegetation changed significantly after water body formation. Water body changes the regional plant community from a simple desert vegetation type before the water delivery, primarily dominated by Nitraria tangutorum Bobr, into reed meadows and salinized meadows around water surface. (4) Because of the formation of a water body and regional vegetation, a cold-island effect was evident during the present study, which improved the regional climate. The mean temperature 500m around water body decreased by 55.67%, and the humidity tripled. The influence of the water surface formation on wind speed was evident, which strengthened the surface erosion of the water surface. Artificial water delivery greatly improved the regional ecological environment of Qingtu Lake; however, due to the uncertainty of water delivery policy and its adjustment strategy, the relevant negative effects of blown sand and regional diversity of species should be addressed in future research. 参考文献 相似文献 引证文献

Dynamics of land surface temperature (LST) in response to land use and land cover (LULC) changes in the Weigan and Kuqa river oasis, Xinjiang, China

Land use and land cover (LULC) changes caused by human activities have strong influences on regional environment. Land surface temperate plays an important role in studying the impact of LULC changes on regional environment. In this paper, remotely sensed thermal infrared data were used to assess land surface temperature (LST) in the Weigan and Kuqa river oasis, Xingjiang, one of the important agricultural areas in the northwestern China. The present study deals with the extraction of LST and the relationship between LULC changes using Landsat 5 TM acquired on September 25, 1989, and September 6, 2011. The results indicate that the surface temperature of water body, bare land, and desert changed significantly between 1989 and 2011. In general, the LST was lower in 1989 than in 2011. There were no lower, higher, and highest temperature zones in 1989. However, the minimum temperature was 10.7 °C in 1989 and 15.8 °C in 2011. The maximum temperature was 29.3 °C in 1989 and 41.8 °C in 2011. Regarding the LULC types, the desert features in the Gobi Desert warmed more quickly than the oasis. So, the temperature of the oasis was lower than the surrounded areas, resulting in a so-called “cold island” phenomenon. Oasis cold island effect index (OCIEI) shows that stability of oasis had rising trend from 1989 to 2011. In addition, the impact of LULC changes on LST was analyzed and the driving forces were also analyzed from 1977 to 2011. This study is significant for further understanding of the energy exchange status of soil-plant-atmospheric system and the regional heat distribution in arid and semi-arid areas of the northwest China.

Oasis cold island effect and its influence on air temperature: a case study of Tarim Basin, Northwest China

Oasis effect can improve the regional climate and habitability of an arid region. In this study, we explored the cold island effects of oases distributed along the edge of Tarim Basin by analyzing the oasis cold island effect (OCIE) intensity, spatial-temporal variation of OCIE, factors influencing the OCIE and impacts of OCIE on air temperature using geographical statistics and GIS methods based on the MODIS land surface temperature, land use/cover change (LUCC) and observed air temperature data. Results showed that all the oases in the Tarim Basin exhibited cold island effects, with the OCIE intensity highest in summer (−9.08°C), followed by autumn (−4.24°C) and spring (−3.85°C). The total area of oasis cold island (OCI) and the comprehensive OCIE index showed the same seasonal change trend as the OCIE intensity. However, the changing trends in areas of OCI with strong, medium and weak OCIEs were inconsistent across different seasons. Farmland and water areas were found to be the key contributors that affected the OCIE, and the area and aggregation metrics of these two land use/cover types directly contributed to the OCIE. By contrast, natural vegetation, such as forest and grassland, almost had no contribution to the OCIE. Simulation of observed air temperature data showed that if farmland is replaced by forest or grassland in the oasis, the mean, maximum and minimum air temperatures will increase significantly. This heating effect will be higher in summer (reaching 1.14°C to 2.08°C) and lower in spring and autumn. Moreover, the heating effect of farmland being replaced by forest will be higher than that of farmland being replaced by grassland. These results can provide a basis for understanding the cold island effect of oases in arid regions.

Change in urban wetlands and their cold island effects in response to rapid urbanization

The cold-island effect of urban wetlands has received increasing attention in recent years due to its important role in the alleviation of urban heat islands. Hangzhou, a representative rapidly urbanizing city with rich wetlands in China, was selected as a case study for researching the changes that the urban wetlands have undergone and their impact on the urban thermal environment. Land surface temperature (LST) was acquired from the thermal infrared data of Landsat 5 Thematic Mapper (TM) images in 1990, 1995, 2000, 2006, and 2010, using the single-channel method. The results are as follows: 1) considering the changes in land use, the urban wetlands located to the west of Hangzhou have decreased significantly during 1990–2010 because of rapid urbanization. In the Xixi Wetland, the change in land use was relatively small and most of the water body and vegetation were preserved. However, to the east of the Xixi Wetland, large areas of water body and vegetation have been replaced by built-up land as a result of the urbanization process; 2) considering the change in LST, it was found from land surface temperature retrieval that the changing spatial pattern of the thermal field was highly correlated with land use changes. Low temperature regions of the eastern Xixi Wetland were gradually eroded by high temperature regions, and the centroid of the heat island in East Xixi was found to be constantly shifting westward. In addition, the difference in LST between the Xixi Wetland and East Xixi has increased; 3) considering the impact factors for this area, land use structure and patch shape were found to have a significant impact on LST, shown by the results of multiple linear stepwise regressions. Increasing the size of the wetlands in urban planning is considered to be the most effective measure in alleviating the urban heat island effect. Moreover, reducing the spatial complexity of landscape patches also contributes to the alleviation of the urban heat island effect.

Numerical Simulation on Oasis Effect over Northwestern China

The characteristics of air temperature, circulation and energy budget of Jinta Oasis are simulated by WRF model, which is the weather research and forecast model of NCAR. The results show that the WRF model has good quality in simulating the diurnal characteristics of surface layer temperature, wind fields, net radiation, sensible heat flux and latent flux. In addition, the model initial fields were also modified by observations of soil temperature and moisture in order to improve the simulations in this study due to important roles of the soil moisture and temperature playing in affecting the cold island effect, the wet island effect properties and surface energy budget balance over the oasis in arid area. Then, the microclimate characteristics and local thermal circulation generated by inhomogeneous underlying surface over Jinta Oasis are analyzed.

城市典型水域景观的热环境效应

城市热岛效应是当前快速城市化进程中最具代表性的生态环境问题之一。热岛效应进一步影响着城市气候变化与城市可持续发展。现存大量研究证明了土地覆被改变导致的热辐射变化及人为热释放共同作用产生了城市热岛。然而,当前对缓解城市热岛效应要素的研究并不多见。以上海市中心城区为例,首先基于SPOT5影像的分类,提取了城市水域景观,再利用Landsat 7的ETM+的热红外波段,定量反演了城市地表热环境温度,然后利用GIS的空间分析功能,探讨了城市水域景观对热环境的影响。研究揭示水域景观在城市热环境中表现出明显的低温效应,而面状水域景观的热环境效应要强于线状河流景观。面状水域景观对热环境影响随着与热岛中心距离的增加而明显降低,此外还受到周围土地覆被的影响。线状河流景观的宽度与流经区域共同决定了其对城市热环境的影响能力。因此,在城市规划设计中,从缓解城市热岛效应出发,水域生态功能区的形态与空间设置可作为考虑因素之一。;Rapid urban expansion has profoundly impacted on urban biodiversity, ecosystem functions, regional climate change, and the quality of life. One of the ecological consequences of urban expansion is the Urban Heat Island (UHI) phenomenon, which is formed when higher atmospheric and surface temperatures in urbanized areas are observed over the surrounding rural area. Urban thermal environment problems caused by UHI have some further impacts on energy consumption, human health and urban sustainable development. As a synthesis representation of urban environment effect, UHI is jointly determined by the physical properties of land surface and heat release by related socioeconomic activities. Within the urbanized area there are diverse landscape types, such as urban building landscape, road landscape, green space, water body, and so on. Among various urban landscape types, the thermal environment effect of water landscape is quite different. It is important to study how the water body might influence the urban thermal environment. The SPOT 5 and Landsat 7 ETM+ images are applied to derive the spatial pattern of urban water landscape and land surface temperature in Shanghai, and spatial analysis technique will be used to explore the thermal environment effect of water landscape. An intense urban heat island effect is identified in Shanghai City, with its center located on the west bank of Huangpu River. At the same time, a cold island effect is detected for the water landscape patches and corridors. Statistical significance is not found between area and perimeter of water patches (or river corridors) and their impact on local thermal environment. However, the water patch has a stronger thermal environment effect than the river corridor. The impact of water patch decreases as the distance to UHI center increases. For instance, the temperature of water patch in Luxun Park (the closest to the UHI center among all water patches) is 3.65℃ lower than the average temperature of its surrounding region, with only 2.60℃ lower than the average temperature of the region where Century Park is located, which is much further to the UHI center. Besides the distance to the UHI center, the impact of water patch on nearby area is also determined by the land surface composition. For instance, the surrounding area with more vegetation has a lower temperature than the area with more impervious surface. River corridors also influence the local thermal environment. Huangpu River, Suzhou River, Yunzao River and Chuanyang River are compared based on a buffering method, with the river width and the location of the river corridor as the two key factors on the local thermal environment. Flowing through UHI center and with the largest river width, Huangpu River has much higher impact on the thermal environment of the surrounding areas. The findings in this study are helpful to provide some effective policy implications for urban planning and design.

Runoff simulations using water and energy balance equations in the lower reaches of the Heihe River, northwest China

Methods for reconstruction of river runoff have been an important component of paleo-climatology and paleo-hydrology. The lower Heihe River was studied from 2002 to 2008 to reconstruct the annual average runoff at the Zhengyi Gorges hydrological station using measured data and improved water and energy balance equations. The results indicate that the reconstructed annual runoff and the measured runoff values are not equivalent. However, the difference between reconstructed and measured runoff values is within 10 %, which suggests that water and energy balance models can successfully reconstruct runoff from rivers in arid regions. Regional differences imply that parameters must be corrected when applying water and energy balance equations to prevent large errors. In addition, the latent heat of evaporation in arid lakes is greater than their net radiation, according to latent and sensible heat calculations, which demonstrates the existence of the “cold island effect”.

Evaluation of oasis stability in the lower reaches of the Tarim River

Oasis stability in the lower reaches of the Tarim River was assessed at the landscape scale (including changes in landscape pattern and land use in the oasis) and at the regional scale (including the cold-island effect and NDVI of the oasis) based on the methods of landscape ecology, GIS and Remote Sensing (RS). Thematic Mapping (TM) remote sensing images from 1990, 2000 and 2009 were employed along with the related meteorological and hydrological data pertaining to the reclamation area of the oasis in the lower reaches of the Tarim River. The results indicated that landscape heterogeneity and oasis com- plexity increased between 1990 and 2000. The comprehensive index of the degree of land use, the aver- age index of the cold-island effect, NDVI value and oasis stability all decreased. However, the change trends in the indices referred to above were opposite between 2000 and 2009, and oasis stability was en- hanced to some extent.

Analysis on the interaction between turbulence and secondary circulation of the surface layer at Jinta oasis in summer

The kinetic energy variations of mean flow and turbulence at three levels in the surface layer were calculated by using eddy covariance data from observations at Jinta oasis in 2005 summer. It is found that when the mean horizontal flow was stronger, the turbulent kinetic energy was increased at all levels, as well as the downward mean wind at the middle level. Since the mean vertical flow on the top and bottom were both negligible at that time, there was a secondary circulation with convergence in the upper half and divergence in the lower half of the column. After consideration of energy conversion, it was found that the interaction between turbulence and the secondary circulation caused the intensification of each other. The interaction reflected positive feedback between turbulence and the vertical shear of the mean flow. Turbulent sensible and latent heat flux anomaly were also analyzed. The results show that in both daytime and at night, when the surface layer turbulence was intensified as a result of strengthened mean flow, the sensible heat flux was decreased while the latent heat flux was increased. Both anomalous fluxes contributed to the cold island effect and the moisture island effect of the oasis.

An analysis of oasis stability in arid areas: a case study in the northern slope areas of the Tianshan Mountains

This paper discusses oasis stability at regional scale with a case study in the northern slope areas of the Tianshan Mountains (NSTM). The results showed certain significant aspects. (1) As long as water resources in the oasis keep stable and their utilization efficiency can be maintained or gradually increased, the primary productivity could be continuously increased and the natural primary productivity keeped relatively stable. In this case, it is considered that the oasis is stable and its sustainable development can be achieved at regional scale. (2) Considering the availability of water resources in the oases, the oases on the alluvial-diluvial fans are highly stable. In the alluvial plain downstream of the groundwater overflowing zones the oases are moderately stable and in the lacustrine deltas or dry lacustrine deltas the oases are lowly stable. (3) Enlargement of oases and the increase of water resources and vegetation coverage in the oasis will certainly enhance the 'cold-island effect' of the oasis and increase the stability of oases.

Numerical simulations of land surface physical processes and land-atmosphere interactions over oasis-desert/Gobi region

A land-surface physical process model was coupled with a mesoscale atmospheric model. This coupled model was then used to simulate the interactions between land and the atmosphere, including surface temperature, net radiation, sensible heat flux and latent heat flux over a desert/Gobi with an oasis in northwestern semiarid regions in China. Comparisons between observations and simulations were made over the oasis and the desert/Gobi, respectively. Both cold island effect and wet island effect, the so-called oasis effect, were observed and simulated. Lower temperature, higher specific humidity and weaker turbulent transfer were present over the oasis than the desert/Gobi. A subsidence occurred over the oasis, leading to a thermally-generated mesoscale circulation.

Temporal and spatial variation and stability of the oasis in the Sangong River Watershed, Xinjiang, China

Starting with the change of the land cover and the landscape patterns as well as the cold-island effect of the oasis, the temporal and spatial variation and the stability of the oasis of the alluvial-diluvial-fan/alluvial-plain type in the Sangong River watershed are researched by using the theories and methods of GIS, RS and landscape ecology based on the aerial photos in 1978 and 1987, the TM images in 1998 and the meteorological and hydrological data of the watershed. The results show that (ⅰ) the land cover of the whole oasis changes rapidly in a big amplitude, and there is an obvious temporal variation; (ⅱ) during the period of 1978—1987, the diversity and the variation of the oasis landscapes were increased but the stability of the oasis was decreased, the diversity of the oasis landscapes, however, has been decreased, but the stability has increased since 1987; (ⅲ) the cold-island effect of the oasis in the Sangong River watershed has been gradually increased since the 1960s, which reveals that the stability of the oasis has been obviously increased viewed from the angle of climate.

Research on the microclimate characteristics and cold island effect over a reservoir in the Hexi Region

On the basis of analysis of the microclimate characteristics over a reservior in the Hexi Region, a new concept for the effect of the lake cold island is advanced. The physical mechanism and practical significance of the effect have also been analyzed.