Research on soil water content (SWC) has involved a wide range of disciplines and attracted constant attention. Current literature reviews primarily focus on a specific type of research on SWC and few systematic studies have been performed to fully evaluate the development and changes in hotspots of SWC research. In this study, a bibliometric analysis and visualization are used to understand the development of SWC research in countries of Europe, Asia, Oceania, and North America. The research data came from the Web of Science database and the time span was 1987–2021. Since 1987, the numbers of international SWC research papers have increased rapidly. The United States and China have the closest exchanges and most publications in the field of SWC. Keyword network maps indicated that early research on SWC was mostly in small-scale farmlands and woodlands, with diverse research hotspots including those focused on SWC stress, soil physical modeling, soil hydrothermal processes, and SWC measurement. Due to climate change, remote sensing technology development, and policies, research on SWC gradually focused on watershed, regional, and global scales, with research hotspots including those focused on evapotranspiration, land–air energy exchange, and remote sensing satellite inversion of SWC products. In addition, in recent years, the research of SWC and SMAP has attracted considerable attention worldwide. The United States has more influence in the SWC sector than China. Although the number of articles that have been published by European countries was small, the influence of those papers should not be underestimated.
The oasis-desert transition zone (TZ) is an ecological buffer zone between a mobile desert and an oasis, which are important in reducing the forward mobility of sand dunes and wind and sand hazards in an oasis. In this study, the Dunhuang Oasis and its TZ in the Hexi Corridor (China) were examined. Based on the annual normalized vegetation index (NDVI) at each buffer distance of the TZ from 1987 to 2015, combing the watershed hydrology, oasis crop cultivation structure and industrial economic status, partial least squares regression models and a correlation analysis were used to examine the spatial and temporal changes in the vegetation gradient of the oasis TZ and the factors influencing those changes. (1) Spatially, the NDVI values in the TZ generally decreased gradually before stabilizing with a buffer distance (average decrease of 0.01–0.03 per 300 m). (2) Temporally, the mean values of the NDVI in the TZ show an overall wavelike variation across years. The annual average maximum NDVI value was 0.11 in 1987, whereas the annual average minimum value was 0.07 in 2014. (3) During the 1987–2015, runoff, tourist populations and water consumption for orchards were significantly and positively correlated with the NDVI; the year-end arable land area and the total industrial output value were significantly and negatively correlated with the NDVI; the rural per capita net income and water consumption for grain planting were not significantly and positively correlated with the NDVI; water consumption for the sum of vegetable and melon planting, water consumption for cotton planting, urbanization and rural populations were not significantly and negatively correlated with the NDVI. (4) The farm TZ NDVI is more strongly influenced by human activities than the undisturbed natural TZ.
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