Spatiotemporal differentiation and evolution trend of critical climatic variables in different ecological regions of...

Under the background of intensifying global changes, the evolution of climate trends has received signi-ficant attention. Few studies have conducted a comprehensive evaluation of the temporal dynamics of essential climate parameters across diverse ecological zones in China. Based on the data from 1525 stations spanning China's mainland between 1961 and 2021, we employed the Theil-Sen slope method, Mann-Kendall trend test, and spatial analysis methodologies to analyze the spatiotemporal patterns and trends of critical climate parameters within four ecological regions: the northeast humid and semi-humid ecological region (Ⅰ), the southern humid ecological region (Ⅱ), the northern arid and semi-arid ecological region (Ⅲ), and the Qinghai-Tibet Plateau ecological region (Ⅳ). The findings revealed that the spatial heterogeneity of climate variables across the four regions was more pronounced than their temporal variability, with the former exhibiting moderate to strong variability and the latter predominantly showing weak variability. Except for relative humidity, the intra-annual variations of other climate variables (precipitation, air temperature, vapor pressure deficit, net surface radiation, and potential evapotranspiration) all follow unimodal curves, with peaks typically occurring between May and August. The highest probability of peak occurred in July. From 1961 to 2021, temporal trends in climate variables showed significant differences among different regions. Precipitation increased in all four regions, but was only significant in Region Ⅳ (0.62 mm·a^-1). Air temperature significantly increased in all regions, with annual rises ranging from 0.02 (Region Ⅱ) to 0.03 ℃ (Regions Ⅰ, Ⅲ, and Ⅳ). Relative humidity significantly declined by 0.03%·a^-1 (Regions Ⅰ and Ⅳ) to 0.05%·a^-1 (Region Ⅲ). The vapor pressure deficit increased by 0.5 (Region Ⅰ) to 0.8 Pa·a^-1 (Region Ⅲ). The net radiation significantly decreased by 2.1 (Region Ⅳ) to 4.4 MJ·m^-2·a^-1 (Region Ⅰ). Annual potential evapotranspiration significantly decreased by 0.99 mm·a^-1 in Region Ⅰ and significantly increased by 0.40 mm·a^-1 in Region Ⅳ. China was experiencing a "warming and drying" trend as indicated by air temperature and relative humidity, while changes in air temperature and precipitation indicated an overall "warming and wetting" trend, particularly in Region Ⅳ.