Lake evolution and its implication for environ-mental changes in China during 1950?2000

Lakes in China have undergone considerable environmental changes during the past 50 years, e.g. lake level, water area changes, as did in the past several thousands years. The enhanced human activities, such as land reclamation, application of chemical fertilizer, land use and cover, irrigation and industrialization in the catchment etc., have played an im-portant role on the recent decades’ changes of these lakes, although constrained to a great extent by the natural impact. Comparative study on variations of lake volume (water level, depth and area) in the eastern and western lake regions of China during 1950–2000 indicated that, lake volume in the eastern region had approximately undergone a two-stage change, i.e. a dramatic decrease from the 1950s to 1970s, and a continuous increase between the 1980s and 1990s; while, in the western region, lake volume had been decreasing nearly all the time. Further studies on some typical lakes concluded that, climatic change was a primary factor for the variations of lake volume during the past 50 years, although human activities showed important effect.     

Transmutation of ancient settlements and environmental changes between 6000–2000 aBP in the Chaohu Lake Basin,East China

Based on the temporal-spatial distribution features of ancient settlement sites from the middle and late Neolithic Age to the Han dynasty in the Chaohu Lake Basin of Anhui Province, East China, using the methods of GIS combined with the reconstructed paleoenvironment by the records of lake sediment since Holocene, the transmutation of ancient settlements with response to environmental changes in this area has been discussed. Studies show that the main feature of transmutation of ancient settlements from the middle and late Neolithic Age to the Han Dynasty was that the distribution of settlements in this area changed from high altitudes to low ones and kept approaching the Chaohu Lake with the passage of time. These could be the response to the climate change from warm-moist to a relatively warm-dry condition during the middle Holocene, leading to the lake level fluctuations. The large area of exposed land provided enough space for human activities. These indicate that the above changes in geomorphologic evolution and hydrology influenced by climate conditions affected the transmutation of ancient settlements greatly. The distribution pattern of settlement sites was that the number of sites in the west was more than in the east. This pattern may be related to the geomorphologic conditions such as frequent channel shifting of the Yangtze River as well as flood disasters during the Holocene optimum. Therefore, climate change was the inducement of the transmutation of ancient settlements in the Chaohu Lake Basin, which exerted great influence on the distribution, expansion and development of the ancient settlements.     

Glacier changes in the Sanjiangyuan Nature Reserve of China during 2000–2018

The glaciers in the Sanjiangyuan Nature Reserve of China (SNRC) are a significant water resource for the Yangtze,Yellow,and Mekong rivers.Based on Landsat Thematic Mapper(TM)/Operational Land Imager (OLI) images acquired in 2000,2010,and 2018,the outlines of glaciers in the SNRC were obtained by combining band ratio method with manual interpretation.There were 1714 glaciers in the SNRC in 2018,with an area of 2331.15±54.84 km2,an ice volume of 188.90±6.41 km3,and an average length of 1475.4±15 m.During 2000-2018,the corresponding values of glaciers decreased by 69,271.95±132.06 km2,18.59±8.83 km3,and 84.75±34 m,respectively.Glaciers in the Yangtze River source area witnessed the largest area loss (-154.45 km2),whereas glaciers in the Mekong River source area experienced the fastest area loss (-2.02％·a-1) and the maximum reduction of the average length (-125.82 m).Overall,the retreat of glaciers in the SNRC exhibited an accelerating trend.Especially,the loss rate of glacier area in the Yellow River source area in 2010-2018 was more than twice that in 2000-2010.The glacier change is primarily attributed to the significant rise in temperature during the ablation period.Some other factors including the size,orientation and terminus elevation of glaciers also contributed to the heterogeneity of glacier change.     

Transmutation of ancient settlements and environmental changes between 6000?2000 aBP in the Chaohu Lake Basin, East China

Based on the temporal-spatial distribution features of ancient settlement sites from the middle and late Neolithic Age to the Han dynasty in the Chaohu Lake Basin of Anhui Province, East China, using the methods of GIS combined with the reconstructed paleoenvironment by the records of lake sediment since Holocene, the transmutation of ancient settlements with response to environmental changes in this area has been discussed. Studies show that the main feature of transmutation of ancient settlements from the middle and late Neolithic Age to the Han Dynasty was that the distribution of settlements in this area changed from high altitudes to low ones and kept approaching the Chaohu Lake with the passage of time. These could be the response to the climate change from warm-moist to a relatively warm-dry condition during the middle Holocene, leading to the lake level fluctuations. The large area of exposed land provided enough space for human activities. These indicate that the above changes in geomorphologic evolution and hydrology influenced by climate conditions affected the transmutation of ancient settlements greatly. The distribution pattern of settlement sites was that the number of sites in the west was more than in the east. This pattern may be related to the geomorphologic conditions such as frequent channel shifting of the Yangtze River as well as flood disasters during the Holocene optimum. Therefore, climate change was the inducement of the transmutation of ancient settlements in the Chaohu Lake Basin, which exerted great influence on the distribution, expansion and development of the ancient settlements.     

China＇s economic development stage and its spatiotemporal evolution： A prefectural-level analysis

As important mechanisms of regional strategy and policy,prefecture-level regions have played an increasingly significant role in the development of China’s economy.However,little research has grasped the essence of the economic development stage and the spatio-temporal evolution process at the prefecture level;this may lead to biased policies and their ineffective implementations.Based on Chenery’s economic development theory,this paper identifies China’s economic development stages at both national and prefectural levels.Both the Global Moran I index and the Getis-Ord Gi* index are employed to investigate the spatio-temporal evolution of China’s economic development from 1990 to 2010.Major conclusions can be drawn as follows.(1) China’s economic development is generally in the state of agglomeration.It entered the Primary Production Stage in 1990,and the Middle Industrialized Stage in 2010,with a ’balanced-unbalanced-gradually rebalanced’ pattern in the process.(2) China’s rapid economic growth experienced a spatial shift from the coastal areas to the the inland areas.Most advanced cities in mid-western China can be roughly categorized into regional hub cities and resource-dependent cities.(3) Hot spots in China’s economy moved northward and westward.The interactions between cities and prefectures became weaker in Eastern China,while cities and prefectures in Central and Western China were still at the stage of individual development,with limited effect on the surrounding cities.(4) While the overall growth rate of China’s economy has gradually slowed down during the past two decades,the growth rate of cities and prefectures in Central and Western China was much faster than those in coastal areas.(5) Areas rich in resources,such as Xinjiang and Inner Mongolia,have become the new hot spots of economic growth in recent years.For these regions,however,more attention needs to be paid to their unbalanced industrial structures and the lagging social development against the backdrop of the rapid economic growth,driven predominantly by the exploitation of resources.     

Spatiotemporal changes in frequency and intensity of high-temperature events in China during 1961–2014

In this study, we explored spatial patterns and the temporal trends in high-temperature events (HTEs) for the mainland of China during 1961–2014 based on a daily- maximum surface-air-temperature dataset of 494 stations and nonparametric trend detection methods. With three thresholds of 35°C (HTE35), 37°C (HTE37), and 40°C (HTE40), HTEs occurred in 82%, 71%, and 37% of the surveyed stations and showed an overall increasing trend in both frequency and intensity during 1961–2014. In northern and southeastern China, HTEs showed a significant increasing trend in both frequency and intensity, whilst a decreasing trend for both was observed in central China. Despite such regional heterogeneity, HTEs overwhelmingly presented three-phase characteristics in all three representative regions and throughout China; the phases are 1961–1980, 1980–1990, and 1990–2014. Both frequency and intensity of HTEs have strongly increased during 1990–2014 at 54.86%, 48.38%, and 23.28% of the investigated stations for HTE35, HTE37 and HTE40, respectively. These findings implied that HTEs adaptation should be paid further attention in the future over China because the wide spread distribution of HTEs and their increasing trends in both frequency and intensity during recent decades might pose challenges to the sustainability of human society and the ecosystem.     

Modeling the spatio-temporal changes in land uses and its impacts on ecosystem services in Northeast China over 2000–2050

Land use and its dynamics have attracted considerable scientific attention for their significant ecological and socioeconomic implications. Many studies have investigated the past changes in land use, but efforts exploring the potential changes in land use and implications under future scenarios are still lacking. Here we simulate the future land use changes and their impacts on ecosystem services in Northeast China (NEC) over the period of 2000–2050 using the CLUE–S (Conversion of Land Use and its Effects at Small regional extent) model under the scenarios of ecological security (ESS), food security (FSS) and comprehensive development (CDS). The model was validated against remote sensing data in 2005. Overall, the accuracy of the CLUE–S model was evaluated at 82.5%. Obtained results show that future cropland changes mainly occur in the Songnen Plain and the Liaohe Plain, forest and grassland changes are concentrated in the southern Lesser Khingan Mountains and the western Changbai Mountains, while the Sanjiang Plain will witness major changes of the wetlands. Our results also show that even though CDS is defined based on the goals of the regional development plan, the ecological service value (ESV) under CDS is RMB 2656.18 billion in 2050. The ESV of CDS is lower compared with the other scenarios. Thus, CDS is not an optimum scenario for eco-environmental protection, especially for the wetlands, which should be given higher priority for future development. The issue of coordination is also critical in future development. The results can help to assist structural adjustments for agriculture and to guide policy interventions in NEC.     

Natural capital accounting in Xi’an City of western China during 1995–2011

As one of the most important metropolitan areas in China, Xi＇an City plays a leading role in the development of the western regions. To impede the decision and policy prefer- ences for environmental and ecological factors, this paper took account of the natural capital depletion of Xi＇an City during 1995-2011, considered in terms of constant 1990 price levels. The results are as follows. （1） Natural capital depletion in Xi＇an City consistently increased from1995 to 2011, increasing from 14.31x108 yuan to 42.28x108 yuan, with an average an- nual growth rate of 12.22%. The primary component of natural capital depletion in Xi＇an City was the cost associated with fossil fuel resource depletion, while the cost associated with ecological services contributed the least to the total cost. （2） During 1995-2011, the proportion of natural capital depletion to Xi＇an City in Yanta and Lianhu districts dropped, whereas in counties such as Gaoling County, Chang＇an District and Lintong District, it increased. In 2011, the proportion of natural capital depletion varied between the different counties： Yanta District （15.75%）, Weiyang District and Lianhu District （10%-15%）, Huxian County, Xincheng District, Beiling District, Chang＇an District, Baqiao District, and Gaoling County （5%-10%）, and in Lintong District, Lantian County, Zhouzhi County and Yanliang District, it was 〈5%. （3） The spatial pattern of natural capital depletion varied with different perspectives, for example, from a total value perspective, a nuclear pattern around the administrative center of Xi＇an City was evident, whereas from a density per capita of natural capital depletion perspective, a bi-nuclear spatial distribution visible in 1995 had become a poly-nuclear distribution by 2011. Conversely, from a density per hectare perspective, a ＂core-edge＂ pattern characterized by three circles was observed. （4） The natural capital depletion relative to GDP curve was in accordance with the environmental Kuznets curve, while the proportion of natural capital de- pletion to GDP was the highest in circle III and the lowest in circle I.     

Construction of the homogenized temperature series during 1910–2014 and its changes in Hunan Province

Based on the statistical method and the historical evolution of meteorological stations, the temperature time series for each station in Hunan Province during 1910–2014 are tested for their homogeneity and then corrected. The missing data caused by war and other reasons at the 8 meteorological stations which had records before 1950 is filled by interpolation using adjacent observations, and complete temperature time series since the establishment of stations are constructed. After that, according to the representative analysis of each station in different time periods, the temperature series of Hunan Province during 1910–2014 are built and their changes are analyzed. The results indicate that the annual mean temperature has a significant warming trend during 1910–2014 and the seasonal mean temperature has the largest rising amplitude in winter and spring, followed by autumn, but no significant change in summer. Temperature variation over Hunan Province has several significant warm-cold alternations and more frequent than that in whole China. Annual and seasonal mean temperatures except summer and autumn have abrupt warming changes in the recent 100 years. The wavelet analysis suggests that the annual and four seasonal mean temperatures in recent 100 years have experienced two climatic shifts from cold to warm.     

Lake Area Changes and the main causes in the hinterland of Badain Jaran Desert during 1973–2010,China

Lake area information in the Badain Jaran Desert in 1973, 1990, 2000, and 2010 was obtained by visual interpretation and water index analysis of remote sensing images, based on the spatial and temporal characteristics of lake area changes during 37 years. Results indicated that the nttmber of lakes declined from 94 to 82 and the total surface area was reduced by 3.69 km2 during 1973-2010. The desert lake area reduced by different degrees in different periods, but this occurred most rapidly during 1973-1990. According to the statistics of lake area changes, lake area decreases mainly occurred in the lakes with areas less than 0.2 km2, while the areas of lakes greater than 0.9 km2 only fluctuated. The changes of lake areas were probably due to changes in the quantity of underground water supplies rather than the effects of local climate change or human factors.     

Variability of atmospheric freezing level height derived from radiosonde data in China during 1958–2005 and its impact to cryosphere changes

Atmospheric air temperature data from 92 stations in China’s radiosonde network were used to analyze changes in the freezing level height (FLH), glacier snow line, and ice edge from 1958–2005 (48 years) and to examine the impact of these changes on the cryosphere. In general, the FLH, glacier snow line, and ice edge exhibited latitudinal zonation, declining from south to north. Trends in the FLH, glacier snow line, and ice edge showed spatial heterogeneity during the study period, with prevailing upward trends. Temporally, the FLH, glacier snow line, and ice edge trends differed on various time scales.     

Urban land expansion and its driving factors of mountain cities in China during 1990–2015

Land expansion of mountain cities in China is not systematically studied yet. This study identified 55 major mountain cities at and above prefecture level, and analyzed the land expansion characteristics and driving forces, based on visually interpreted data from TM images in 1990, 2000, 2010 and 2015. From 1990 to 2015, total built-up land area of the mountain cities increased by 3.87 times, 5.56% per year. The urban land growth was apparently accelerated after 2000, from 4.35% per year during 1990–2000 increased to 6.47% during 2000–2010 and 6.2% during 2010–2015. Compared to the urban population growth, the urban land expansion rate was 44% higher. As a result, the urban land area per capita increased, but it was still within the government control target, and also was much lower than the average of all cities in China. Urban development policy, changes to administrative divisions, GDP and population growth, and road construction were identified as the major driving forces of land expansion. Terrain conditions were not found a relevance to the urban land expansion rate during 1990–2015, but had a significant impact on the layout and shape, and also probably on the urban land efficiency.     

Change in summer daily precipitation and its relation with air temperature in Northwest China during 1957–2016

On the basis of the summer daily-precipitation meteorological data collected from weather stations across Northwest China from 1957 to 2016, this study evaluated the trends in 12-daily precipitation indices in the summer season and their relations with air temperature. Precipitation-event intensity, which was averaged over the total study area, increased in recent decades although the total precipitation continuously decreased. In particular, intensity generally decreased in the northern and eastern parts and increased in the southern and western parts of the study area. None of the 12 precipitation indices was significantly correlated with temperature in Xinjiang; R95 N(number of events with precipitation greater than the long-term95 th percentile), RX1 day(greatest 1-day total precipitation), PI(simple daily intensity), and R10(number of heavy-precipitation days) were significantly and positively correlated with temperature in Qinghai–Gansu. However, low correlation coefficients were observed. In the Loess Plateau, P(total precipitation), WS(maximum number of consecutive wet days),R95 N, and WD(number of wet days) were significantly and negatively correlated with temperature, whereas Gini(gini concentration index) and DS(maximum number of consecutive dry days) were significantly and positively correlated with temperature. Results of the study suggested that climate shift was evident in terms of daily precipitation, and the study area faced new challenges involving precipitation-event intensity increasing in the southwestern part and unevenly dispersing in the northwest.     

Monitoring periodically national land use changes and analyzing their spatiotemporal patterns in China during 2015–2020

Journal of Geographical Sciences - High-resolution mapping and monitoring of national land use/cover changes contribute significantly to the knowledge of the interaction between human activities...     

Urban expansion and intra-urban land evolution as well as their natural environmental constraints in arid/semiarid regions of China from 2000–2018

Rapid urbanization has occurred in arid/semiarid China, threatening the sustainability of fragile dryland ecosystems; however, our knowledge of natural environmental constraints on multiscale urban lands in this region is still lacking. To solve this issue, this study retrieved 15-m multiscale urban lands. Results indicated that urban area increased by 68%during 2000–2018, and one-third of the increase was contributed by only three large cities.The coverage of impervious surface area(ISA) and ve...     

Detecting spatio-temporal changes of arable land and construction land in the Beijing-Tianjin corridor during 2000–2015

Journal of Geographical Sciences - Rapid peri-urbanization has become a new challenge for sustainable urban-rural development worldwide. To clarify how unprecedented urban sprawl at the...     

Grassland coverage inter-annual variation and its coupling relation with hydrothermal factors in China during 1982–2010

GIMMS (Global Inventory Modeling and Mapping Studies) NDVI (Normalised Difference Vegetation Index) from 1982 to 2006 and MODIS (Moderate Resolution Imaging Spectroradiometer) NDVI from 2001 to 2010 were blended to extract the grass coverage and analyze its spatial pattern. The response of grass coverage to climatic variations at annual and monthly time scales was analyzed. Grass coverage distribution had increased from northwest to southeast across China. During 1982–2010, the mean nationwide grass coverage was 34% but exhibited apparent spatial heterogeneity, being the highest (61.4%) in slope grasslands and the lowest (17.1%) in desert grasslands. There was a slight increase of the grass coverage with a rate of 0.17% per year. Increase in slope grasslands coverage was as high as 0.27% per year, while in the plain grasslands and meadows the grass coverage increase was the lowest (being 0.11% per year and 0.1% per year, respectively). Across China, the grass coverage with extremely significant increase (P<0.01) and significant increase (P<0.05) accounted for 46.03% and 11% of the total grassland area, respectively, while those with extremely significant and significant decrease accounted for only 4.1% and 3.24%, respectively. At the annual time scale, there are no significant correlations between grass coverage and annual mean temperature and precipitation. However, the grass coverage was somewhat affected by temperature in alpine and sub-alpine grassland, alpine and sub-alpine meadow, slope grassland and meadow, while grass coverage in desert grassland and plain grassland was more affected by precipitation. At the monthly time-scale, there are significant correlations between grass coverage with both temperature and precipitation, indicating that the grass coverage is more affected by seasonal fluctuations of hydrothermal conditions. Additionally, there is one-month time lag-effect between grass coverage and climate factors for each grassland types.     

Differential changes in precipitation and runoff discharge during 1958–2017 in the headwater region of Yellow River of China

Maintenance of steady streamflow is a critical attribute of the continental river systems for safeguarding downstream ecosystems and agricultural production.Global climate change imposes a potential risk to water supply from the headwater by changing the magnitude and frequency of precipitation and evapotranspiration in the region.To determine if and to what extent the recent climate changes affected streamflow in major river systems,we examined the pattern of temporal variations in precipitation,temperature,evapotranspiration and changes in runoff discharge during 1958–2017 in the headwater region of the Yellow River in northeastern Tibetan Plateau.We identified 1989 as the turning point for a statistically significant 14% reduction in streamflow discharge(P 0.05) for the period 1989–2017 compared with 1958–1988,approximately coinciding with changes in the monthly distribution but not the interannual variations of precipitation,and detected a mismatch between precipitation and runoff after 2000.Both annual precipitation and runoff discharge displayed fourand eight-year cyclic patterns of changes for the period 1958–1988,and a six-year cyclic pattern of changes for the period 1989–2017,with two intensified two-year cyclic patterns in the changes of precipitation and a three-year cyclic pattern in the change of runoff further detected for the later period.Our results indicate that the temporal changes in runoff are not strictly consistent with the temporal variations of precipitation in the headwater region of Yellow River during the period 1958–2017.In particular,a full recovery in annual precipitation was not reflected in a full recovery in runoff toward the end of the study period.While a review of literature yielded no apparent evidence of raised evapotranspiration in the region due to recent warming,we draw attention to increased local retention of rainwater as a possible explanation of differential changes in precipitation and runoff.     

Temporal and spatial changes of temperature and precipitation in Hexi Corridor during 1955–2011

This study is focused on the northwestern part of Gansu Province, namely the Hexi Corridor. The aim is to address the question of whether any trend in the annual and monthly series of temperature and precipitation during the period 1955-2011 appears at the scale of this region. The temperature and precipitation variation and abrupt change were examined by means of linear regression, five-year moving average, non-parameter Mann-Kendall test, accumulated variance analysis and Pettitt test method. Conclusions provide evidence of warming and wetting across the Hexi Corridor. The mean annual temperature in Hexi Corridor increased significantly in recent 57 years, and the increasing rate was 0.27℃/10a. The abrupt change phenomenon of the annual temperature was detected mainly in 1986. The seasonal average temperature in this region exhibited an evident upward trend and the uptrend rate for the standard value of winter temperature indicated the largerst of four seasons. The annual precipitation in the Hexi Corridor area displayed an obviously increasing trend and the uptrend rate was 3.95 mm/10a. However, the annual precipitation in each basin of the Hexi Corridor area did not passed the significance test. The rainy season precipitation fluctuating as same as the annual one presented insignificant uptrend. No consistent abrupt change was detected in precipitation in this study area, but the rainy season precipitation abrupt change was mainly observed in 1968.     

Spatiotemporal changes in vegetation coverage and its driving factors in the Three-River Headwaters Region during 2000–2011简

The Three-River Headwaters Region （TRHR）, which is the source area of the Yangtze River, Yellow River, and Lancang River, is of key importance to the ecological secu- rity of China. Because of climate changes and human activities, ecological degradation oc- curred in this region. Therefore, ＂The nature reserve of Three-River Sou,＇ce Regions＂ was established, and ＂The project of ecological protection and construction for the Three-River Headwaters Nature Reserve＂ was implemented by the Chinese government. This study, based on MODIS-NDVI and climate data, aims to analyze the spatiotemporal changes in vegetation coverage and its driving factors in the TRHR between 2000 and 2011, from three dimensions. Linear regression, Hurst index analysis, and partial correlation analysis were employed. The results showed the following： （1） In the past 12 years （2000-2011）, the NDVI of the study area increased, with a linear tendency being 1.2%/10a, of which the Yangtze and Yellow River source regions presented an increasing trend, while the Lancang River source region showed a decreasing trend. （2） Vegetation coverage presented an obvious spatial difference in the TRHR, and the NDVI frequency was featured by a bimodal structure. （3） The area with improved vegetation coverage was larger than the degraded area, being 64.06% and 35.94%, respectively during the study period, and presented an increasing trend in the north and a decreasing trend in the south. （4） The reverse characteristics of vegetation cov- erage change are significant. In the future, degradation trends will be mainly found in the Yangtze River Basin and to the north of the Yellow River, while areas with improving trends are mainly distributed in the Lancang River Basin. （5） The response of vegetation coverage to precipitation and potential evapotranspiration has a time lag, while there is no such lag in the case of temperature. （6） The increased vegetation coverage is mainly attributed to the warm-wet climate change and the implementation of the ecological protection project.