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Qifei Zhang
College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China

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Journal article
Published: 11 February 2021 in Remote Sensing
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The desert-oasis ecotone, as a crucial natural barrier, maintains the stability of oasis agricultural production and protects oasis habitat security. This paper investigates the dynamic evolution of the desert-oasis ecotone in the Tarim River Basin and predicts the near-future land-use change in the desert-oasis ecotone using the cellular automata–Markov (CA-Markov) model. Results indicate that the overall area of the desert-oasis ecotone shows a shrinking trend (from 67,642 km2 in 1990 to 46,613 km2 in 2015) and the land-use change within the desert-oasis ecotone is mainly manifested by the conversion of a large amount of forest and grass area into arable land. The increasing demand for arable land for groundwater has led to a decline in the groundwater level, which is an important reason for the habitat deterioration in the desert-oasis ecotone. The rising temperature and drought have further exacerbated this trend. Assuming the current trend in development without intervention, the CA-Markov model predicts that by 2030, there will be an additional 1566 km2 of arable land and a reduction of 1151 km2 in forested area and grassland within the desert-oasis ecotone, which will inevitably further weaken the ecological barrier role of the desert-oasis ecotone and trigger a growing ecological crisis.

ACS Style

Fan Sun; Yi Wang; Yaning Chen; Yupeng Li; Qifei Zhang; Jingxiu Qin; Patient Kayumba. Historic and Simulated Desert-Oasis Ecotone Changes in the Arid Tarim River Basin, China. Remote Sensing 2021, 13, 647 .

AMA Style

Fan Sun, Yi Wang, Yaning Chen, Yupeng Li, Qifei Zhang, Jingxiu Qin, Patient Kayumba. Historic and Simulated Desert-Oasis Ecotone Changes in the Arid Tarim River Basin, China. Remote Sensing. 2021; 13 (4):647.

Chicago/Turabian Style

Fan Sun; Yi Wang; Yaning Chen; Yupeng Li; Qifei Zhang; Jingxiu Qin; Patient Kayumba. 2021. "Historic and Simulated Desert-Oasis Ecotone Changes in the Arid Tarim River Basin, China." Remote Sensing 13, no. 4: 647.

Journal article
Published: 20 August 2020 in Remote Sensing
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Global warming has generally led to changes in river runoffs fed by snow and glacier meltwater in mountain ranges. The runoff of the Aksu River, which originates in the Southern Tienshan Mountains, exhibited a positive trend during 1979–2002, but this trend reversed during 2002–2015. Through a comprehensive analysis, this study aims to estimate potential reasons for changes in the runoff of its two contrasting headwaters: the Toxkan and Kumalak Rivers, based on climatic data, the altitude of the 0 °C isotherm, glacier mass balance (GMB), snow cover area (SCA), snow depth (SD) and the sensitivity model. For the Toxkan River, the decrease in spring runoff mainly resulted from reductions in precipitation, whereas the decrease in summer runoff was mainly caused by early snowmelt in spring and a much-reduced snow meltwater supply in summer. In addition, the obvious glacier area reduction in the catchment (decreased to less than 4%) also contributed to the reduced summer runoff. For the Kumalak River, a sharp decrease rate of 10.21 × 108 m3/decade in runoff was detected due to summertime cooling of both surface and upper air temperatures. Reduced summer temperatures with a positive trend in precipitation not only inhibited glacier melting but also dropped the 0 °C layer altitude, resulting in a significant increase in summertime SCA and SD, a slowing of the glacier negative mass balance, and a lowering of the snow-line altitude.

ACS Style

Qifei Zhang; Yaning Chen; Zhi Li; Gonghuan Fang; Yanyun Xiang; Yupeng Li; Huiping Ji. Recent Changes in Water Discharge in Snow and Glacier Melt-Dominated Rivers in the Tienshan Mountains, Central Asia. Remote Sensing 2020, 12, 2704 .

AMA Style

Qifei Zhang, Yaning Chen, Zhi Li, Gonghuan Fang, Yanyun Xiang, Yupeng Li, Huiping Ji. Recent Changes in Water Discharge in Snow and Glacier Melt-Dominated Rivers in the Tienshan Mountains, Central Asia. Remote Sensing. 2020; 12 (17):2704.

Chicago/Turabian Style

Qifei Zhang; Yaning Chen; Zhi Li; Gonghuan Fang; Yanyun Xiang; Yupeng Li; Huiping Ji. 2020. "Recent Changes in Water Discharge in Snow and Glacier Melt-Dominated Rivers in the Tienshan Mountains, Central Asia." Remote Sensing 12, no. 17: 2704.

Journal article
Published: 01 July 2020 in Water
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The aim of this research was to use the standardized runoff index (SRI) with a three-month timescale (SRI-3) to analyze hydrological drought risk in two arid river basins characterized by different runoff regimes, Northwest China. Based on SRI-3, hydrological drought levels for different events were defined through run theory. The hydrological drought risk in the two study basins was then comprehensively assessed using a multidimensional copula function that considered the multivariable joint probability of hydrological drought duration, severity, intensity and peak. Results indicate that: (1) the risk of hydrological drought in the two basins between 1961–2018 periodically changed. There was a slight increase in risk within the Yarkant River Basin, while there was a clear decrease in risk within the Kaidu River Basin. The magnitude of drought in the two basins was relatively low; both basins were dominated by mild to moderate hydrological droughts; (2) the drought probabilities of the Yarkant River Basin and Kaidu River Basin from 1961 to 2018 exhibited a falling-rising-falling pattern and a rising-falling trend through time, respectively. These trends were correlated with changes in precipitation and the area of glacial ice, which presumably influenced the amount and source of runoff in the two basins. Hydrological drought risk in the Yarkant River Basin was higher than in the Kaidu River Basin; and (3) the return period of mild, moderate, severe and extreme drought events was 2 yrs, 8 yrs, 20 yrs, and 60 yrs in the Yarkant River Basin, respectively, and 2 yrs, 8 yrs, 23 yrs and 74 yrs in the Kaidu River Basin, respectively.

ACS Style

Yanyun Xiang; Yi Wang; Yaning Chen; Yifei Bai; Leyuan Zhang; Qifei Zhang. Hydrological Drought Risk Assessment Using a Multidimensional Copula Function Approach in Arid Inland Basins, China. Water 2020, 12, 1888 .

AMA Style

Yanyun Xiang, Yi Wang, Yaning Chen, Yifei Bai, Leyuan Zhang, Qifei Zhang. Hydrological Drought Risk Assessment Using a Multidimensional Copula Function Approach in Arid Inland Basins, China. Water. 2020; 12 (7):1888.

Chicago/Turabian Style

Yanyun Xiang; Yi Wang; Yaning Chen; Yifei Bai; Leyuan Zhang; Qifei Zhang. 2020. "Hydrological Drought Risk Assessment Using a Multidimensional Copula Function Approach in Arid Inland Basins, China." Water 12, no. 7: 1888.

Journal article
Published: 05 February 2020 in Water
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The aim of this research is to adopt the Standardized Precipitation Evapotranspiration Index (SPEI) with three-month timescale (SPEI-3) to analyze drought risk in Central Asia. Based on SPEI-3, a drought event is defined through Run Theory. The multidimensional Copula function based on drought risk is then comprehensively assessed through the multivariable joint probability of drought duration, drought severity, and drought peak. Results indicate as follows: (1) the climate conditions were relatively stable from 1961–1974 and 1979–1995, while they varied from 1974 to 1979 and from 1995 to 2017, during which the study areas experienced recurrent drought. (2) The drought characteristics show noticeable spatial variability, and the severity of drought is larger in the west than in the east in Central Asia; the duration of drought contrasts with the severity of drought spatially. (3) The drought risk in the three-dimensional joint distribution is similar to the analysis using the two-dimensional distributions, and the study area has gone through the process from moderate to slight and then to severe drought risk from 1961 to 2017; the return period studied in this paper was calculated to be 80% probability in about two years.

ACS Style

Leyuan Zhang; Yi Wang; Yaning Chen; Yifei Bai; Qifei Zhang; Zhang. Drought Risk Assessment in Central Asia Using a Probabilistic Copula Function Approach. Water 2020, 12, 421 .

AMA Style

Leyuan Zhang, Yi Wang, Yaning Chen, Yifei Bai, Qifei Zhang, Zhang. Drought Risk Assessment in Central Asia Using a Probabilistic Copula Function Approach. Water. 2020; 12 (2):421.

Chicago/Turabian Style

Leyuan Zhang; Yi Wang; Yaning Chen; Yifei Bai; Qifei Zhang; Zhang. 2020. "Drought Risk Assessment in Central Asia Using a Probabilistic Copula Function Approach." Water 12, no. 2: 421.

Journal article
Published: 17 December 2019 in Sustainability
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There are currently only two methods (the within-growing season method and the inter-growing season method) used to analyse the normalized difference vegetation index (NDVI)–climate relationship at the monthly time scale. What are the differences between the two methods, and why do they exist? Which method is more suitable for the analysis of the relationship between them? In this study, after obtaining NDVI values (GIMMS NDVI3g) near meteorological stations and meteorological data of Inner Mongolian grasslands from 1982 to 2015, we analysed temporal changes in NDVI and climate factors, and explored the difference in Pearson correlation coefficients (R) between them via the above two analysis methods and analysed the change in R between them at multiple time scales. The research results indicated that: (1) NDVI was affected by temperature and precipitation in the area, showing periodic changes, (2) NDVI had a high value of R with climate factors in the within-growing season, while the significant correlation between them was different in different months in the inter-growing season, (3) with the increase in time series, the value of R between NDVI and climate factors showed a trend of increase in the within-growing season, while the value of R between NDVI and precipitation decreased, but then tended toward stability in the inter-growing season, and (4) when exploring the NDVI–climate relationship, we should first analyse the types of climate in the region to avoid the impacts of rain and heat occurring during the same period, and the inter-growing season method is more suitable for the analysis of the relationship between them.

ACS Style

Zhifang Pei; Shibo Fang; Wunian Yang; Lei Wang; Mingyan Wu; Qifei Zhang; Wei Han; Dao Nguyen Khoi. The Relationship between NDVI and Climate Factors at Different Monthly Time Scales: A Case Study of Grasslands in Inner Mongolia, China (1982–2015). Sustainability 2019, 11, 7243 .

AMA Style

Zhifang Pei, Shibo Fang, Wunian Yang, Lei Wang, Mingyan Wu, Qifei Zhang, Wei Han, Dao Nguyen Khoi. The Relationship between NDVI and Climate Factors at Different Monthly Time Scales: A Case Study of Grasslands in Inner Mongolia, China (1982–2015). Sustainability. 2019; 11 (24):7243.

Chicago/Turabian Style

Zhifang Pei; Shibo Fang; Wunian Yang; Lei Wang; Mingyan Wu; Qifei Zhang; Wei Han; Dao Nguyen Khoi. 2019. "The Relationship between NDVI and Climate Factors at Different Monthly Time Scales: A Case Study of Grasslands in Inner Mongolia, China (1982–2015)." Sustainability 11, no. 24: 7243.