Spatiotemporal evolution characteristics of the aridity-humidity boundary in the Hunshandake Sandy Land from 1961 to 2023

The Hunshandake Sandy Land is highly sensitive to climate change, and the spatiotemporal variation of its dry-wet boundary is crucial for the evolution of the regional ecological environment. Based on daily average temperature and daily precipitation data from 14 meteorological observation stations within and around the Hunshandake Sandy Land from 1961 to 2023, we performed an in-depth investigation of the spatiotemporal changes in the dry-wet boundary using a modified Selianinov aridity index. The results indicate the following: (1) Temporally, the annual aridity index in the Hunshandake Sandy Land showed an increasing trend over the past 63 years, reaching a secondary peak in 2023, indicating a prominent intensification of climatic aridification. (2) Spatially, the annual average aridity index exhibited a zonal distribution pattern of “lower in the southeast and higher in the northwest,” with a stronger increasing trend in the western part than in the eastern part. (3) Decadal time scale analysis revealed that the K=1.5 isoline migrated southeastward, with the largest shifts occurring in the 2000s and 2020s. The proportion of arid areas dramatically increased by more than four times, jumping from 1.54% in the 2010s to 7.70% in the 2020s. (4) Analysis based on climatic standard periods indicated that the most severe southeastward displacement of the K=1.5 isoline, with a maximum distance of approximately 95 km, occurred between the 1971-2000 and 1981-2010 periods. The semiarid area reached its maximum proportion, accounting for 73.39%, in the 1991-2020 period.