Evaluation of satellite-based and reanalysis soil moisture products using ground-observations in the Qilian Mountains

Critical to the reliable application of gridded soil moisture (SM) products is a thorough assessment of their quality, particularly in water conservation and supply areas such as Qilian Mountains (QLM). The study systematically evaluated the accuracy of surface soil moisture (SSM) and root-zone soil moisture (RZSM) using 14 ground-based sites in the QLM from 2019 to 2021. The study evaluated seven SSM products, comprising four satellite-based datasets (AMSR2-LPRM, SMOS-IC, SMAP-L3, and ESA CCI) and three reanalysis datasets (SMAP-L4, GLDAS-Noah, and ERA5-Land). Furthermore, the performance of three RZSM products derived from these reanalysis datasets was also examined. For SSM products, reanalysis products generally exhibit higher R (0.56) and lower ubRMSE (0.04 m³/m³) compared to satellite-based products (0.44, 0.05 m³/m³). The SMAP-L3 showed the best performance (<i>R</i> = 0.71), followed by the ERA5-Land and SMAP-L4. For RZSM products, compared to GLDAS and ERA5-Land, SMAP-L4 demonstrated better performance (<i>R</i> = 0.59) and shown greater potential for application in QLM. The average R (0.65) of SSM was highest for grassland sites, attributed to fewer land cover heterogeneity. For forest sites, the SSM performance was generally lowest (average <i>R</i> = −0.11). In Arou site, the superior spatial representativeness of Cosmic ray neutron sensor (CRNS) measurements enhanced the evaluation performance (higher R, lower ubRMSE) of nearly all products. Notably, the comparative evaluation with <i>in-situ</i> data underscored the robustness of CRNS as a reference for SM evaluation and proved its mesoscale applicability. The research aimed to provide a reference for the application of gridded SM products in water resources monitoring and ecosystem services in QLM.