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Understanding the mechanisms underlying drying-wetting cycles and their consequence for vegetation dynamic is important for sustainable eco-environmental development in alpine regions. We investigated these in this paper by taking the Yarlung Zangbo River (YZR) basin in southeast Qinghai-Tibet Plateau as an example. The standardized precipitation evapotranspiration index (SPEI) in the region was calculated using the global land data assimilation system (GLDAS) from 1982 to 2015 to represent the drying-wetting cycles. The spatiotemporal variation of the dry-wet cycles and the responsive vegetation dynamic was investigated using the remotely sensed NDVI (normal difference vegetation index) from GIMMS (global inventory modeling and mapping studies). The results showed that: 1) Spatiotemporal variation of both precipitation and surface air temperature calculated from GLDAS agreed well with the ground-truth data. 2) The spatiotemporal changes in the dry-wet cycles calculated from the SPEI from 1982 to 2015 showed that the YZR basin became increasingly wet from 1982-1999 but changed course in 2000 and has been become increasingly drier since. In particular, the arid areas showed a tendency of wetting whereas the humid areas tended to become drying. 3) The overall vegetation calculated from the NDVI had been in increase from 1982 to 2000 but changed course in 2000 and has been in decline since. In terms of spatial distribution, areas with higher NDVI value represented vegetation degradation, while areas with lower NDVI represented an improvement in vegetation. 4) Approximately 71.83% of the areas saw a positive correlation between the SPEI and NDVI, mainly in the middle and low reaches of the basin which have a high vegetation coverage. Areas showing negative correlation between SPEI and NDVI were small and not statistically significant. The high consistency between spatiotemporal variation of the NDVI and SPEI indicated that the drying-wetting cycles played an important role in vegetation dynamics. 5) The driving forces of the dry-wet cycles were precipitation, surface air temperature, potential evapotranspiration and soil water content, which were consistent with that estimated from SPEI. In addition, the SPEI showed that soil water content was the dominant factor impacting the drying-wetting in 92.17% of the areas in the region. Results of this study have important implications for evaluating water cycles and the associated vegetation dynamics in alpine regions. [ABSTRACT FROM AUTHOR]

Drought has become a problem that is universally faced by global terrestrial ecosystems. Northeast China is dominated by a temperate monsoon climate and located in an area sensitive to global climate changes, and one of the main impacts of climate changes in Northeast China is manifested as drought in growing seasons. The drought area has a gradual increase trend, and drought has become the main agro-meteorological disaster in this region which is also the main maize planting area in China. Drought normalization seriously restricts the stable development of maize production in Northeast China. So in this paper, we took spring maize in Liaoning Province as an example and made clear the drought variation characteristics in different growth stages by using the data of MODIS, FY-3A, relative soil moisture and growth stages and the methods of RS, GIS and statistical analysis. Then we analyzed the correlation between multi-time scale remote sensing indexes and relative soil moisture in different soil depth, and established the remote sensing monitoring index set and models of relative soil moisture for each growth stage and soil depth. The accuracy of the monitoring models was verified and the application research of monitoring the drought of spring maize in Liaoning Province was studied. The results showed that: From 1993 to 2012, drought occurred in each growth stage of spring maize in Liaoning Province and the highly frequent drought occurred in the period from 1999 to 2002. The drought grade in each year was mainly light drought, and the drought was the most serious at milk stage, followed by heading stage. There was no significant correlation between the monitoring indexes and relative soil moisture at sowing and emergence stage, but there was a significant or extremely significant correlation between them at three-leaf and maturity stage. The monitoring index LSWI (land surface water index) had a strong ability to monitor relative soil moisture, followed by WI (water index). Multi-index coordination could improve the monitoring ability of relative soil moisture by remote sensing means, and the monitoring ability at 10-day scale was generally higher than that at 5-day scale and 20-day scale. Based on the monitoring models of soil relative humidity, the drought condition of partial growth stages and soil depth from 2001 to 2004 was monitored. The overall monitoring accuracy was 73.32%, in which the monitoring accuracy of jointing and three-leaf stage was more than 85%. The dynamic monitoring of drought grades in different growth stages in 2000 was realized. The monitoring results were consistent with the agro-meteorological observation records in terms of the growth stages and space. This study would be very significant to improve the capacity of disaster prevention and mitigation by monitoring spring maize accurately and synchronously on a large range. [ABSTRACT FROM AUTHOR]

The changes of lake water resources record the impacts of climate change and human activities on the regional hydrological processes in the changing environment. Especially for inland areas with less precipitation, timely and accurate information on changes in lake water resources are recorded. Environmental evolution has an important reference value. With China’s largest desert freshwater lake-Hongjiannao Lake as an example, based on the 3S (RS, GIS, and GPS, which are remote sensing, global position system, geographic information system) technology, lake water surface area change was analyzed, which provided important scientific guidance for the restoration, protection and utilization of ecological and economic functions of Hongjiannao Lake. However, due to the different sources of data, the uneven technology, the discontinuous time series and the generally short time series, as well as the different monitoring phases, the result analysis on the change of water area of Hongjiannao Lake is quite different and systematic study and overall analysis of long time series of the entire river basin are lacking. Fifteen periods of both basic and RS data collected for Hongjiannao Lake, such as DRG, DLG, DOM, remote sensing images, and paper maps, were selected for analysis over a recent 60-year period (from 1957 to 2015), together with field annotation data and relevant attributes. All the data and images above have passed the geometric correction of digital elevation model data from Shaanxi Surveying and Mapping Archives and Geological Information Bureau of State Bureau of Surveying and Mapping, which have good quality. Different data can meet the high-precision registration requirements of water body information extraction in the study area. Among them, NDWI (normalized difference water index) with better extraction effect was used to extract water body information, which could restrain the vegetation soil while enhance the water body information. To analyze characteristics in spatio-temporal variations and identify trends of the change in lake water area over the period, we comprehensively utilized RS and GIS techniques and adopted spatial data processes, extracted and interpreted information, constructed a massive database, and conducted integrated management and analysis. We also explored major causes that triggered spatio-temporal variations of lake water area by combining climate change and anthropogenic factors from the same period. Results indicated that in a recent 60-year period, the area covered by water significantly changed in the study area. During 1957-1976, the water area continuously increased from 37.6 to 55.53 km2, and reached the maximum value over the entire record of study with increased amplitude of 47.69%. The growth rates in northern and southeastern areas of the lake were relatively fast, followed by other regions. During 1977-1999, the overall water area was stable, approximately 50 km2. During 2000-2015, water area showed a decreasing trend year by year, from 50.27 to 31.05 km2 with decreased amplitude of 38.23%, and all regions showed this shrinking trend except waters near Qibusu River in 2005, in which the reverse occurred and the water area slightly increased. In general, over the last 60 years, the revolution process of the water area of Hongjiannao Lake could be divided into 3 phases corresponding to the annual variability of water area: expanding period (1957-1976), stabilizing period (1977-1999), and shrinking period (2000-2015), showing an overall shrinking trend. The area of lakes and waters has experienced a dynamic trend of expansion-stabilization-atrophy in the recent 60 years, and has shown a significant atrophy situation since 1999 and a strong signal of ecological and hydrological deterioration, deserving attention. Trends in both warming and drying climate may be the major factors, which affect lake water area variation in both expanding and stabilizing periods, and the superimposition of these trends with anthropogenic effects (i.e. a water conservation project construction in the upper streams, coal mining, pavement construction around the lake, and water consumption for irrigation) may be the essential factor leading to water area variations during the shrinking period. [ABSTRACT FROM AUTHOR]

Cultivated land is an important indicator of landscape changes driven by human activities. Mapping the spatio-temporal changes of cultivated lands will help us to understand its corresponding environmental and ecological changes in their downstream areas. The Manas drainage basin is the key area of agricultural region in the northern slope of the Tianshan Mountains. However, the drastic farmland reclamation in the last 50 years makes irrigation water increasing rapidly, leading to environmental degradation in the downstream of the Manas River. In this paper, remote sensing and GIS technologies are used to analyze the spatio-temporal characteristics of farmland changes in the Manas drainage basin under the condition of intense soil-water utilization. Firstly, remote sensing images in 1962, 1977, 1989, 2000 and 2010 are applied to map land use changes with the cognition classification software and manual edition. Then the temporal process and spatial pattern of land cover changes are analyzed by geo-statistics and landscape analysis. On the temporal scale, the cultivated land changes and its mutual transition relationships with other land types are analyzed with areal ratio and transition matrix methods; on the spatial scale, GIS spatial analysis tool and landscape class level index are used to describe the characteristics of farmland expansion or shrinking changes in different regions and different land patches. Finally, hydrological data and irrigation construction data are used to explain the impact of climate change and human activities on the farmland landscape. The results show that: (1) The overall land use changes of the Manas drainage basin in the last 50 years are as follows: cultivated land and built-up areas increase continuously, while the unutilized land, wetland and snow/glacier have been decreasing steadily; grassland area is increasing in the former 20 years and then decreasing gradually in the last 30 years; the intensity of land use changes keeps stable after dramatic changes. (2) The overall cultivated land transformations have shifted from outward and inward transformations to single inward transformation; in inward land types, grassland and unutilized land are the main inward land types to farmland, and woodland and wetland take larger percentages in the first 20 years, while less percentages in the later 30 years; in outward land types, built-up land and grassland are the main outward land types, and grassland and unutilized land have larger percentages in the former 20 years due to cultivated land degradation; the total area of inward land types far exceeds than that of the outward land types, and the cultivated land area is steadily increasing in the last 50 years. (3) The focus of cultivated land expansion has shifted from the margins of cities to desert regions, and the newly-increased farmland gradually from the upstream to the downstream; cultivated land expansion firstly begins at the Changji Hutubi and Manas County in the former 20 years, then shifts to Shawan County, the river's surrounding areas and northern deserts; the cultivated landscapes are characterized from discrete and messy pieces into continuous land patches, so the advantage of cultivated landscape is increasing, while the landscape diversity and heterogeneity are decreasing due to land parcel combinations. (4) The increasing precipitation and runoff in the Manas drainage basin provide more water resource for cultivated land reclamation, and reservoir and irrigation channel construction have positive effects on spatial expansion of the cultivated land; when reservoirs and channels are built up, cultivated land will expand correspondingly in a rapid rate in the next decade, and hence the spatio-temporal processes of farmland expansion have high relations with the irrigation facilities. (5) The increasing water resource induced by climate change cannot keep up with the increasing speed of the farmland, and water resource is in the state of over exploitation; measures must be taken to reduce the amount of irrigated water, so as to improve ecological environments in the downstream of the Manas River. [ABSTRACT FROM AUTHOR]

Cultivated land is an important indicator of landscape changes driven by human activities. Mapping the spatio-temporal changes of cultivated lands will help us to understand its corresponding environmental and ecological changes in their downstream areas. The Manas drainage basin is the key area of agricultural region in the northern slope of the Tianshan Mountains. However, the drastic farmland reclamation in the last 50 years makes irrigation water increasing rapidly, leading to environmental degradation in the downstream of the Manas River. In this paper, remote sensing and GIS technologies are used to analyze the spatio-temporal characteristics of farmland changes in the Manas drainage basin under the condition of intense soil-water utilization. Firstly, remote sensing images in 1962, 1977, 1989, 2000 and 2010 are applied to map land use changes with the cognition classification software and manual edition. Then the temporal process and spatial pattern of land cover changes are analyzed by geo-statistics and landscape analysis. On the temporal scale, the cultivated land changes and its mutual transition relationships with other land types are analyzed with areal ratio and transition matrix methods; on the spatial scale, GIS spatial analysis tool and landscape class level index are used to describe the characteristics of farmland expansion or shrinking changes in different regions and different land patches. Finally, hydrological data and irrigation construction data are used to explain the impact of climate change and human activities on the farmland landscape. The results show that: (1) The overall land use changes of the Manas drainage basin in the last 50 years are as follows: cultivated land and built-up areas increase continuously, while the unutilized land, wetland and snow/glacier have been decreasing steadily; grassland area is increasing in the former 20 years and then decreasing gradually in the last 30 years; the intensity of land use changes keeps stable after dramatic changes. (2) The overall cultivated land transformations have shifted from outward and inward transformations to single inward transformation; in inward land types, grassland and unutilized land are the main inward land types to farmland, and woodland and wetland take larger percentages in the first 20 years, while less percentages in the later 30 years; in outward land types, built-up land and grassland are the main outward land types, and grassland and unutilized land have larger percentages in the former 20 years due to cultivated land degradation; the total area of inward land types far exceeds than that of the outward land types, and the cultivated land area is steadily increasing in the last 50 years. (3) The focus of cultivated land expansion has shifted from the margins of cities to desert regions, and the newly-increased farmland gradually from the upstream to the downstream; cultivated land expansion firstly begins at the Changji Hutubi and Manas County in the former 20 years, then shifts to Shawan County, the river's surrounding areas and northern deserts; the cultivated landscapes are characterized from discrete and messy pieces into continuous land patches, so the advantage of cultivated landscape is increasing, while the landscape diversity and heterogeneity are decreasing due to land parcel combinations. (4) The increasing precipitation and runoff in the Manas drainage basin provide more water resource for cultivated land reclamation, and reservoir and irrigation channel construction have positive effects on spatial expansion of the cultivated land; when reservoirs and channels are built up, cultivated land will expand correspondingly in a rapid rate in the next decade, and hence the spatio-temporal processes of farmland expansion have high relations with the irrigation facilities. (5) The increasing water resource induced by climate change cannot keep up with the increasing speed of the farmland, and water resource is in the state of over exploitation; measures must be taken to reduce the amount of irrigated water, so as to improve ecological environments in the downstream of the Manas River. [ABSTRACT FROM AUTHOR]