Abstract. China has experienced rapid urbanization and rapid development of economy in the past decades, resulting in severe damage to the urban ecological environment, causing changes in the urban thermal environment and triggering the urban heat island effect. Moreover, the heat island effect has become a hot topic for scholars. The urban heat island effect refers to the phenomenon that the urban surface temperature is significantly higher than that of surrounding suburbs due to the interaction of man-made and natural. The city is considered to be the largest man-made ecosystem. Its heat island effect will not only change the growth habit of urban vegetation, but also affect the outer environment of urban buildings, it further influences human life and has a great negative impact on human health. Therefore, the study of the spatial-temporal variation characteristics of urban heat island effect and its influencing factors can provide data support for the environmental quality control and urban planning of local government departments. Based on the surface temperature remote sensing product data, we studied the spatial distribution characteristics of urban heat island effect in Wuhan from 2001 to 2013, by calculating the temperature difference between the highest and lowest temperatures and the average interval method for heat island classification. We conducted a trend analysis of vegetation cover from 2001 to 2013 initially explore the effects of vegetation cover n heat island effect. The results showed that: (1) From 2001 to 2013, the intensity of heat island in Wuhan was strong in the city center, weaker surrounding city center and the weakest in the suburbs; From 2001 to 2011, the intensity of heat island in Wuhan city was significantly weaken, among which Huangpi, Xinzhou, Jiangxia, Hannan and Caidian district were weaken, and the urban heat island effect of the city center was enhanced; From 2011 to 2013, the intensity of heat island in Wuhan city presented an increasing trend, among which Huangpi district, Xinzhou district and Caidian district were the most obvious, and the urban heat island effect was slightly weaken. (2) Between 2001 and 2013, the vegetation cover in Huangpi district and Xinzhou district increased significantly, and the vegetation cover in the downtown, Jiangxia district and Dongxihu district decreased significantly, corresponding to the urban heat island effect of Wuhan increased volatility. Our results showed that the spatial distribution of urban heat island effect in Wuhan city fluctuated with time during the study period, and the vegetation cover had a significant influence on it.
Abstract. Drought is an extremely complex natural disaster phenomenon. Sustained drought will lead to the aggravation of water shortage, food production reduction, land desertification and ecological crisis, which will have a great impact on social and economic development, industrial and agricultural production and ecological environment. In recent years, human activities have intensified, the global climate has been warming, and the frequency and intensity of extreme events such as drought have been continuously strengthened, which has been widely concerned by scholars at home and abroad. The Beijing-Tianjin-Hebei region, as the political and cultural center of China, is seriously affected by the drought, which has a certain impact on the social economy of the region. Therefore, it is of great practical significance to carry out remote sensing drought monitoring and understand the temporal and spatial characteristics of drought. Based on MOD13A2 and MOD11A2 in MODIS products, this paper constructed the NDVI-Ts feature space to obtain the Temperature Vegetation Dryness Index (TVDI) in Beijing-Tianjin-Hebei region, and analyzed the spatial and temporal variation characteristics of drought in Beijing-Tianjin-Hebei region from 2001 to 2014 with TVDI as the drought index. The results showed that: (1) the NDVI-Ts feature space in the Beijing-Tianjin-Hebei region showed that when the value of NDVI rose from 0 to 1, the maximum temperature of the surface gradually decreased, while the minimum temperature gradually rose. Both of them had a linear relationship with NDVI, and their spatial shape was similar to a triangle, indicating that the study of drought in Beijing-Tianjin-Hebei was effective by using this spatial feature; (2) the Beijing-Tianjin-Hebei region experienced drought every year in the period of 2001–2014, and the drought was more serious in 2001, 2004, 2008, 2009, 2011 and 2012; (3) The drought in the Beijing-Tianjin-Hebei region was widespread, and the severely arid regions were mainly concentrated in the southern and central regions. In terms of drought intensity, the most frequent occurrences in the period of 2001–2014 were Xingtai, Hengshui, Shijiazhuang, and Handan, and the annual drought in 14 years; the least number of occurrences was Chengde, a total of 4 times; the number of occurrences was second only to Chengde, Tangshan, Zhangjiakou, Qinhuangdao, a total of 7 times. Our results indicated that the Beijing-Tianjin-Hebei region was prone to drought and the drought degree was severe.
Abstract. The source region of the Yellow River is an important ecological barrier in China. Since the 1990s, under the influence of various factors, its runoff has decreased and the ecological environment has deteriorated, which has attracted great attention of governments. Vegetation is the general term of plant communities covering the surface, which is the natural link between the atmosphere, water and soil. It plays an important role in air regulation, soil conservation and maintaining the stability of the whole ecosystem. Therefore, the study on the differential characteristics and topographic influencing factors of alpine grassland change in the source region of the Yellow River can provide reference for the ecological environment protection in -this region in the future. Based on the remote sensing data of MODIS NDVI, we studied the spatial distribution pattern and temporal variation characteristics of vegetation coverage in the source region of the Yellow River from 2000 to 2009 by means of maximum synthesis method, pixel dichotomy model method and trend analysis method. Furthermore, combined with DEM topographic elevation data, we discussed the influence of topographic factors such as elevation, slope and aspect on fractional vegetation cover (FVC) change. The results showed that: (1) From 2000 to 2009, the FVC in the source region of the Yellow River fluctuated upward, showing the spatial distribution characteristics of the southeast region > the central region > the northwest region; (2) During the ten years from 2000 to 2009, the almost constant of FVC accounted for the largest area, and the areas with increasing FVC mainly concentrated in the northeast and northwest of the studied region, the areas with reduced vegetation coverage were scattered in various places in the studied region, mainly in the form of minimal patches or spots; (3) Different terrain factors had different effects on FVC and the effect of altitude on FVC changes was significantly greater than that of slope and aspect. With the increase of altitude, the proportion of significant reduction in FVC increased firstly and then decreased, while the proportion of significant increase in FVC was decreasing and the proportion of almost unchanged in FVC was increasing; With the increase of slope, the proportion in the above three cases (significant reduction, significant increase and almost unchanged in FVC) was increased, decreased gradually and fluctuated respectively. Under different aspect, the proportion in the above three cases varied little, fluctuating only within 1%.
Abstract. China's economy has experienced rapid development in the past few decades, and economic development has also brought serious pollution problems, which has attracted wide attention of scholars at home and abroad. Based on the data of global PM2.5 remote sensing products and China's economic development from 1998 to 2016, the temporal and spatial variations of PM2.5 concentration in China from 1998 to 2016 were analyzed, and the response of PM2.5 concentration in China to economic development was studied. The results showed that the average annual PM2.5 concentration in 1998–2016 showed the spatial distribution characteristics of high in the East and low in the west; during 1998–2016, PM2.5 increased significantly in most regions, but decreased significantly in Inner Mongolia, Shaanxi, Ningxia and Gansu, while PM2.5 did not change significantly in some parts of the central region; during 1998–2007, PM2.5 concentration in most regions of China experienced rapid economic development. The concentration of PM2.5 in a few areas such as Inner Mongolia decreased significantly, while that in Yunnan, Sichuan and Inner Mongolia did not change significantly. During the 10 years of economic slowdown in China (2008–2016), the downward trend of PM2.5 concentration in China was expanding. The concentration of PM2.5 in the central and southern regions decreased or did not change significantly, except in the northwest and a few northeast regions. The change of PM2.5 concentration responds obviously to economic development, but the response of different regional economic development to the change of PM2.5 concentration is different.
Abstract. The source region of the Yellow River is an important source of water conservation in the Qinghai-Tibet Plateau. It is also an animal husbandry base that has a major impact on China. Its ecological environment changes will have a major impact on the safe and sustainable development of water use in Asia. The alpine grassland is an important part of the ecosystem of the Yellow River source area, and the spatial differentiation characteristics of the plaque have important indication significance for the ecological environment succession. In this paper, the alpine grassland in the source region of the Yellow River is taken as the research object. Based on the aerial image of the unmanned aerial vehicle, the EGI threshold method is used to extract the vegetation patches and the bare plaques to obtain high-precision field monitoring data, and the landscape ecology principle is used to analyze the four types of alpine grassland. The morphological characteristics of plaques in different grassland types are studied, and the spatial indications of spatial sequences are used to study the ecological significance of plaque succession. The results show that the number of plaques in swamp meadows, alpine meadows, degraded meadows and alpine grassland increase significantly, the degree of fragmentation increase, and the area of vegetation patches decrease significantly. The area of bare plaque increase significantly as the main trend; the distribution and dominance of landscape plaques are analyzed; the swamp meadow have the highest spread, the best aggregation, and the largest proportion of vegetation plaque, the highest degree of dominance, alpine grassland Conversely; in terms of the complexity of landscape patch shape; the area-weighted shape index and the area-weighted fractal dimension increase with the order of swamp meadows, alpine meadows, degraded meadows and alpine grasslands, tending to be complex plaque space. The ecological risk intensity index of alpine grassland in the source region of the Yellow River varies greatly, and the ecological risk of alpine grassland is high. The results of this study provide data support for elucidating the mechanism of spatial differentiation of alpine grass plaques, provide scientific assistance for grassland monitoring and management in the source area, and it provides an important basis for further discussion on ecological system protection, animal husbandry economy and sustainable development of alpine grassland in China. At the same time, it provides important theoretical support and ecological indication significance for the understanding of the alpine grassland ecosystem succession in the source area of the Yellow River.
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