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Arid Land Geography ›› 2026, Vol. 49 ›› Issue (6): 1203-1214.doi: 10.12118/j.issn.1000-6060.2025.390

• Vegetation and Pedology • Previous Articles     Next Articles

Applicability and spatiotemporal variation analysis of SMAP ascending products to soil moisture in Qaidam Basin

LI Suyun1,2(), ZHU Cunxiong1,2,3(), WANG Jing4, CHEN Guoqian1,2, SHI Feifei1,2   

  1. 1 Key Laboratory of Disaster Prevention and Mitigation of Qinghai Province, Xining 810001, Qinghai, China
    2 Qinghai Institute of Meteorological Sciences, Xining 810001, Qinghai, China
    3 Ping’an District Meteorological Bureau, Haidong City, Haidong 810600, Qinghai, China
    4 Xining Meteorological Bureau, Xining 810001, Qinghai, China
  • Received:2025-07-08 Revised:2025-09-28 Online:2026-06-25 Published:2026-06-29
  • Contact: ZHU Cunxiong E-mail:lisuyun_qh@163.com;zhucunxiong_2008@126.com

Abstract:

Soil moisture is a critical regulator of terrestrial water cycles, energy exchange, and carbon fluxes. However, soil moisture observations in plateau regions are constrained by challenges, such as uneven station distribution and sparse measured data. However, soil moisture active passive (SMAP) satellite products provide important data support for large-scale monitoring in these regions. The applicability of SMAP ascending soil moisture data was first evaluated using multiple accuracy-evaluation metrics, after which spatiotemporal soil moisture responses in Qaidam Basin were analyzed via Theil-Sen median+Mann-Kendall trend tests, rescaled range analysis, and coefficient of variation. Results show the following: (1) SMAP soil moisture products exhibit dry-overestimation and wet-underestimation biases in the Qaidam Basin. The correlation coefficient with the measured soil moisture content is 0.6543, with an unbiased root-mean-square error of 0.0928 m3·m-3. Although this does not meet the expected target accuracy, it remains a viable reference. (2) SMAP soil moisture products exhibit different performances across varying vegetation covers, peaking under medium coverage, followed by low coverage, and declining significantly under high coverage. (3) SMAP soil moisture products effectively capture moisture surges, accurately reflecting the entire process involving precipitation infiltration, soil moisture accumulation, and extinction. (4) From 2015 to 2024, Qaidam Basin grassland soil moisture shows a space distribution in the growing season: It first decreases, after which it increases from the basin center toward its four peripheries on average for many years, exhibiting a space distribution of the trend-change rate. Spatially, trend rates increase in the southeast, decrease slightly in the central region, and increase marginally in the northwest. The stability is dominated by medium and relatively low fluctuations. Additionally, the spatial distribution pattern shows a “wide transition zone and a concentrated extreme zone”. Projections indicate that Qaidam Basin soil moisture will generally maintain a persistent increasing trend.

Key words: SMAP, soil moisture, applicability, spatiotemporal variation, Qaidam Basin