Temporal stability of soil water storage in three landscapes in the middle reaches of the Heihe River, northwestern China

Temporal stability of soil moisture is important for the sustainability of compound ecosystems where different landscapes coexist and interact with each other. In this study, an arid region composed of desert, cropland and wetland in northwestern China was selected to evaluate the temporal stability of soil water storage (SWS) and identify the representative locations of the spatial mean SWSs in diverse soil layers of each landscape. Soil water storages of 0–1, 1–2 and 2–3 m soil layers were estimated from volumetric water contents measured at fixed intervals in a regular 1 × 1 km grid in an area of 100 km2 from May 2011 to December 2012 using a neutron probe. Spearman’s rank correlation and relative difference analysis both indicated the increasing temporal stability of SWS with depth in the three landscapes. Locations with the lowest standard deviation of relative differences accurately estimated the spatial mean SWSs after providing constant offsets. At the representative locations in the three layers of the desert, the cumulative probabilities for clay, silt, sand and soil organic carbon contents were <0.25, <0.25, >0.75 and between 0.5 and 0.75, respectively, and the respective values in the cropland were >0.75, between 0.5 and 0.75, between 0.25 and 0.5 and between 0.5 and 0.75. An a priori approach was then proposed to select the potential representative locations in larger areas of the desert and cropland, from which actual representative locations can be identified after long period measurement. This strategy is economic and labor saving, and can benefit upscaling studies.