Purpose The 400 mm isohyet, as the boundary between semi-humid and semi-arid regions, has severe spatiotemporal variations that inevitably generate a series of economic, social and ecological impacts. However, traditional studies primarily measured the coarse variations (latitude and longitude) of the 400 mm isohyet. Due to the complexity and variability of annual isohyet fluctuations, finescale changes (multidirection and magnitude) remain difficult to quantify. Thus, this study aims to systematically quantify the fluctuation characteristics of the 400 mm isohyet. Design/methodology/approach To address this limitation, a high-precision long-term precipitation product was constructed and evaluated. In addition, this study introduced a boundary fluctuation detection method to quantitatively analyze the spatiotemporal dynamics of the isohyet. Findings The 400 mm isohyet in the eastern region of China exhibited a significant westward shift (−0.036° yr−¹, p 0.05) and a slight southward shift (−0.025° yr−¹). The most pronounced oscillations of the decadal 400 mm isohyet occurred in the border areas of Heilongjiang, Jilin and Inner Mongolia. Temporally, between the 1980s and the 2000s, the isohyet in Northeast China clearly retreated southeastward, reflecting a transition toward a warmer and drier climate. In contrast, during the 2010s, the isohyet in Northeast China region, the Inner Mongolia and the Great Wall region, the Loess Plateau region and the Qinghai-Tibet Plateau advanced northwestward compared to the 2000s, indicating a shift toward a warmer and wetter climate. Practical implications This study strengthens and enhances the understanding of the spatiotemporal variation characteristics and patterns of agro-pastoral boundaries in the context of climate change, providing a scientific basis for climate change modeling, mitigation and adaptation strategies. Originality/value This study introduced a refined method to detect the spatiotemporal characteristics of 400 mm isohyet variations, overcoming previous challenges in capturing multidirectional changes in isohyet and filling a gap in the quantitative detection of geographical boundaries with temporal and spatial fluctuation characteristics.
Li et al. (Fri,) studied this question.