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Recent research shows that China is experiencing significant greening, with afforestation initiatives being the main cause. Quantitative calculation of vegetation change influencing factors and evaluation of the contribution of afforestation to vegetation greening in China are critical to coping with climate change and improving the implementation and efficacy of forestry projects. We investigated the temporal and spatial dynamics of the Normalized Difference Vegetation Index (NDVI) from 1982 to 2020, and quantified the contribution of afforestation initiatives, a typical human activity, to the dynamic changes of vegetation. The results showed that NDVI in China has primarily increased in the last 39 years. 57% of the pixels increased, 27% were stable and unchanged, and 16% decreased. Climate change was responsible for 72.34% of vegetation restoration, while human activities were responsible for 27.36% of vegetation restoration, according to residual analysis. In the future, only 14% of the regions showed continuous growth of the NDVI, while the remaining regions showed obvious antipersistence (59% will go from increasing to decreasing, and 22% will go from decreasing to increasing). The contribution of climate factors to vegetation change will decrease in the future, and human activities will become more complex. Except for Huaihe River and Taihu Lake (SPHRTL), other forestry projects showed an increasing trend of NDVI after the implementation of ecological engineering. However, due to differences in climate conditions and ecological engineering implementation, there are differences in the benefits of forestry projects. Some forestry project areas still have obvious vegetation degradation, and appropriate forestry management is necessary. This work provides a quantitative analysis of vegetation change and its driving factors in China, which will help to cope with future climate change and provide a reference for the implementation and management of ecological projects. [ABSTRACT FROM AUTHOR]

Climate change and human activities have changed a number of characteristics of river flow in the northwest of China. Numerous problems such as water resource shortage, drying up of rivers, water pollution are the direct consequences of these changes. In this paper, we used the example of Yulin city in northwest China to assess the spatio-temporal characteristics and driving forces of annual river flow changes. Our research was based on the long-term time series of hydrological data from 1956 to 2005, to analyse annual flow in four main rivers (Kuye River, Tuwei River, Wuding River and Jialu River). The river flow depends upon the runoff characteristics of the river catchment, therefore we used variation ratio, variation index, unevenness, Runoff-Concentration Degree (RCD) and Runoff-Concentration Period (RCP) to determine the change in runoff characteristics of the four main rivers flows of the Yulin city. We tested the tendency of runoff by the Mann-Kendall non-parameter statistical method to obtain the temporal evolution law. At the same time, Kriging spatial interpolation and GIS were used to derive the spatial evolution law. The dates of climate change (precipitation) and human activities were also used to calculate the driving forces for annual runoff changes of the rivers’ catchments. Through the accumulation curves and multi-recursive techniques, we built the correlation between precipitation and runoff. The driving factors for annual runoff change were then calculated by using the runoff coefficient method. Results showed that the distribution of annual runoff was uneven and had a small accumulation in July and August, especially in Kuye River, and there seemed to be a significant reducing trend in annual runoff. Isolines and the thematic map of Mann-Kendall tests U(R) revealed that the Tuwei River's catchment is the most affected catchment, with annual runoff substantially changed. At the 5% significance level, precipitation did not significantly drop compared with annual runoff. We also found that precipitation is not the only factor responsible for the decreased annual runoff. Therefore we included human activities affect in this case study by using the past 25 years land use, water conservancy and urbanisation data. We discriminated the impacts of climate change and human activities on the surface runoff by multi-recursive analysis method and runoff coefficient method. The results showed that human activities are the direct cause for the changes of river runoff. The results of the study also revealed that the Wuding and Jialu rivers had the most and the least changes in the runoff respectively; this phenomenon should be seriously considered for future water resources planning and management. [ABSTRACT FROM PUBLISHER]

Qilian Mountain as an important ecological security barrier and water connotation area in China, Research on its vegetation NPP driving mechanism can provide reference for ecological security protection in northwest China. Based on Qilian Mountain MOD17A3 remote sensing data from 2000-2019, using one-dimensional linear regression, partial correlation analysis, multiple linear regression, residual analysis and land transfer matrix. The spatial and temporal dynamics of vegetation NPP in the Qilian Mountain and its correlation with precipitation, temperature and human activities were analyzed, and quantified the effects of climate change and human activities on vegetation NPP. The results show that: 1) from 2000 to 2019 vegetation NPP in Qilian Mountains had an overall fluctuating upward trend and decreased from east to west, with a multi-year average of 138.54 g C·m−2·a−1 and an average annual increase of 1.67 g C·m−2·a−1; 2) vegetation NPP was positively correlated with precipitation and temperature, with precipitation having a more significant effect on it; 3) the area of grassland in LUCC increased the most and contributed 183.12% to vegetation NPP, while the area of unused land decreased the most and its contribution to vegetation NPP was −119.6%; 4) In the vegetation recovery area, climate change and human activities explained 89% and 11% of the vegetation recovery, respectively. While in the vegetation degradation area, they explained 22% and 78% of the vegetation degradation, respectively. [ABSTRACT FROM AUTHOR]

The variation of hydrological processes has been extensively discussed worldwide, yet little is known about the relative impact of human activities, and the precipitation–water level relationship in urbanized, watery areas. Thus, the change in water level and the influential variables are analysed for 1960–2014 in the urbanized and watery Taihu Basin, China. The results indicate that the water level displays a significant increasing trend. Furthermore, low-oscillation and high-oscillation periods were found to have occurred in the 1960s–1970s and 2000s, respectively, by the quantile perturbation method. A strong relationship was shown between water level and precipitation in the 1960s–1980s, especially in the flood season. Since then, human activities, such as land-use change, river system degradation and hydrological structures, have played distinct roles and caused more than 82% of the annual and flood-seasonal water level variation. The results may provide a more comprehensive understanding of the hydrological processes and provide a good reference for flood control. [ABSTRACT FROM AUTHOR]

The aim of this study is to reveal statistical characteristics and exceedance probability of discharge under the combined effect of climate change and human activities. The study is conducted in the Xiaoqing River in Jinan, China, based on data of discharge, land-use types and precipitation from the period 1970–2016. A multivariate joint probability distribution of the data is established to test the univariable, bivariable and trivariable change points. These are then used to calculate and analyse the risk probability of discharge exceeding the specific values under different conditions of precipitation and land-use type. The results show that the change point calculated by trivariate joint distribution can reduce the disturbance of the change point obtained with the univariable or bivariable approach and reflect the changes of various factors in the hydrological processes more objectively. When the land-use type is taken into consideration, the trivariate distribution can reflect the variation of hydrological processes more reasonably. [ABSTRACT FROM AUTHOR]