Does urban growth mean the loss of greenness? A multi-temporal analysis for Chinese cities.

Urban growth is recognized as the conversion of vegetated surface to built-up surface. However, there is still no consensus about the urbanization-induced dynamic of vegetation greenness in view of existing literatures. In this study, we aimed to empirically investigate whether urban growth mean the loss of vegetation greenness. We selected 340 Chinese cities as the study areas, relied on consistent multi-temporal remotely sensed data and adopted linear regression analysis, annual growth area, Tail-Sen slope and Mann-Kendall models. Results show that although vegetation greening generally lagged behind urban growth in the monitoring period, a tendency of their consistent speeding up can be observed over time. By categorizing four forms and four trends of vegetation greenness dynamics related to urban growth, we revealed the diversity of Chinese cities. The former focused on the velocity of urban growth and vegetation greenness dynamics within newly urbanized area in three phases, i.e., 2003-2008, 2008-2013 and 2013-2018. The latter focused on the interannual trends of vegetation greenness dynamics among the previously existing and newly urbanized areas. The key finding is that, in over 85 % of the cities, we measured an increase of vegetation greenness along with urban growth. In addition, our detailed results allow quantifying the impact of urbanization in Chinese cities on vegetation protection and sustainable development.

Spatial and temporal variability of soil erosion in the black soil region of Northeast China from 2000 to 2015.

The black soil region in Northeast China is an important production base of commodity grain. However, soil erosion is a major threat that has caused a decline in arable land area and productivity and a series of environmental problems in recent years. To understand the current situation of soil erosion and its changes in the whole black soil region, including six treatment regions, we used the spatial-temporal analysis of soil erosion from 2000 to 2015 and the overlay analysis with its drivers; additionally, soil erosion was evaluated qualitatively with the integrated evaluation method, and its change was indicated by the soil erosion change index (SECI). We found that soil erosion that caused soil loss occurred in each treatment region mainly at the light level in 2015. Water erosion, the most widely distributed erosion type, affected the largest area, while most serious erosion at intensive or higher levels stemmed from wind erosion. Although the situation of water erosion was improved in 2015 compared to that in 2000, the overall situation of soil erosion was worse due to the deterioration of wind and freeze-thaw erosion. Grassland, woodland, and cultivated land changes, such as the conversion from grassland to cultivated land, from woodland to sparse woodland and from dry land to paddy land, revealed these changes to a great extent.

Chinese cropland losses due to urban expansion in the past four decades.

Since 1970s, China has experienced the large-scale losses of croplands during urban expansion process, which has drawn great attentions to Chinese government. Although in-depth studies about cropland losses have been executed widely, relatively little attention has been paid to describe long term and high frequency influences of urban expansion on it and reveal its differences systematically. Based on remote sensing and GIS technology, we quantified, analyzed, and mapped cropland losses in China due to urban expansion from the national, administrative-level, population-size, and city scales. Results indicated that (1) Since the 1970s, croplands were the primary contributor to urban expansion in China, and their losses due to urban expansion underwent five obvious stages. The consciousness of cropland protection is being strengthened continuously and has developed from the initial to the deep execution stages. (2) Cropland losses were unbalanced in China, with the loss magnitude, rate, and influences on urban expansion positively related to the administrative-level and large population-size. That is, obvious losses always emerged in cities with high administrative-level and large population-size. (3) Seven basic trends of cropland losses were quantitatively recognized, which was conducive to the formulation of different policies or strategies for cropland protection for different cities.