Abstract
The Ebinur Lake watershed is an important ecological barrier for environmental changes in the Junggar Basin in Xinjiang Uygur Autonomous Region (XUAR). Due to the tremendous changes in the underlying surface environment of the watershed in the past few decades, the watershed has become a typical region of ecological degradation. Drought affects the surface dynamics and characterizes the regional dry and wet environments, while the dynamic variation in lakes and vegetation are indicators of dynamic changes in land surfaces. Thus, a quantitative assessment of the response of lakes and vegetation to drought conditions at multiple temporal scales is critical for assessing the potential impacts of regional climate change on terrestrial ecosystems and ecological restoration. The standardized precipitation evapotranspiration index (SPEI), the spectral water index (NDWI) and the normalized difference vegetation index (NDVI) were used to analyse the evolution of drought, the variation in lake surface area and the sustainable variation in vegetation. Furthermore, we quantitatively evaluated the response patterns of vegetation to droughts of multiple temporal scales (1-, 3-, 6-, 12-, 24-month). The conclusions showed that (1) overall, the area of Ebinur Lake experienced drastic fluctuations, and the lake area has decreased significantly since 2003, with a dynamic area of 817.63 km2 in 2003 and 384.60 km2 in 2015, and the lake area had shrank severely. (2) The interannual variation of wet and dry changed alternately during the observation period, and persistent drought events occurred from 2006 to 2010 across the Ebinur Lake watershed. (3) The vegetation area of cultivated land expanded continuously across the watershed, and the grassland degraded severely. (4) The changes in lake surface area are significantly correlated with the inflow water volume (correlation coefficient = 0.64, P < 0.01). (5) The vegetation of different terrestrial ecosystems exhibited heterogeneous responses to multiple temporal scales of drought in different seasons. The percentage was 72.78% of the total area, which showed a correlation between vegetation and drought conditions during the growing season period, and there were more impacts of drought on vegetation, with values as high as 64.33% of the area in summer, than those in other seasons.
Highlights
Ebinur Lake is the largest salt lake in the Xinjiang Uygur Autonomous Region (XUAR)
To evaluate the classification accuracy of the normalized difference water index (NDWI), in this paper, the maximum likelihood classification (MLC) method based on Landsat-5,7,8 was applied for water body extraction, and the result indicated that the region of interest (ROI) separability values of water and non-water were all greater than 1.99, which can be used for accuracy verification by establishing an error matrix for the NDWI
The multiple temporal scales drought indices were calculated to assess the wetting and drying evolution, the dynamic variation of lake surface area and response pattern of vegetation to drought conditions in the watershed; This study provided an sensitivity assessment of different terrestrial ecosystems to multiple temporal scales drought
Summary
Ebinur Lake is the largest salt lake in the XUAR. Lakes are a crucial surface water resource and an indispensable part of the wetland environment that plays a role in maintaining the balance of arid regional ecological environments[18]. It can be seen that the long-term dynamic monitoring of lake water resources is of great significance for understanding the arid regional hydrological process Vegetation, as another indicator of drying and wetting changes in the regional environment, provides a link between the soil and atmosphere and plays an essential role in the exchange of energy on the surface of the Earth; vegetation affects the carbon cycle, hydrological cycle and regional human activities[23]. Reviewing previous studies on the effects of climate on lake area and vegetation dynamics, the link between drought and vegetation growth and changes in inland lake area may help us further understand the effects of drought In this context, this research attempts to fill in the gaps in the effects of drought climate on regional ecological environments, vegetation and lake dynamics in arid regions. The aim of this paper is to clarify the following points: 1) identify the dynamic evolution of the surface of arid inland salt lakes over the past 16
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