Evolution of Research on Global Soil Water Content in the Past 30 Years Based on ITGinsight Bibliometric Analysis

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.