Soil moisture, as an important variable affecting water–heat exchange between land and atmosphere, is an important feedback to climate change. Soil moisture is of great concern in Northern China, where arable land is extensive, but water resources are distributed unevenly and extremely sensitive to climate change. Using measured soil moisture data collected by the China Meteorological Administration from 164 stations during 1980–2021, we explored the drivers of soil moisture variation by analyzing its spatiotemporal variability using linear regression, partial correlation analysis, and geostatistical methods. The results indicated that (1) soil moisture increased from northwest to southeast in Northern China, with the lowest soil moisture in the IM; (2) the overall trend of soil moisture in most regions decreased, especially in the arid northwest and northeast China. However, soil moisture in some regions began to increase gradually in recent years, such as in northwestern Xinjiang and the central-eastern part of IM; and (3) soil moisture in the whole region was negatively correlated with temperature and sunshine duration and positively correlated with precipitation and relative humidity. The results of the study can provide valuable guidance for timely agricultural irrigation and the adjustment of cropping structures, thereby ensuring agricultural production and food security.

To systematically study the quantitative relationship between natural enemies and pests, this paper used grey relational analysis method, angular cosine coefficient method, fuzzy similarity priority ratio method and correlation coefficient method to analyze the closeness of the quantitative relationship between natural enemies and Empoasca onukii Matsuda in “Anjibaicha”, “Huangshandayezhong” and “Longjing 43” tea plantations. The conclusions obtained by the grey relational analysis method were used as a criterion to compare the sum of the rankings of the top three natural enemies, Plexippus paykulli, Tetragnatha squamata and Ebrechtella tricuspidata, thus comparing and discussing the similarities and differences between the conclusions obtained by the four research methods. The angular cosine coefficient method and grey relational analysis method yielded no major differences in conclusions, followed by the correlation coefficient method, with the fuzzy similarity priority ratio method yielding more varied results. According to the ranking analysis of the close relationship between the number of E. onukii and its natural enemies, Tetragnatha squamata, Hylyphantes graminicola and Ebrechtella tricuspidata are the first three natural enemies closely related to the number of E. onukii. This paper is an attempt to compare the consistency of research results of various research methods, which provides a reference for selecting research methods in analyzing the quantitative relationship between natural enemies and pests.