A team in the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) used the temporal stability analysis to upscale point-scale measurements to represent mean areal SWC on two typical karst hillslopes. The researchers found that the hillslope with more shrub cover was wetter than the hillslope with mixed grass-shrub cover. The difference was related to the soil texture, soil hydraulic permeability, and topography.

“Through a comparison of values obtained with the Spearman correlation coefficient (r_s), standard deviation of mean relative difference (SDRD), and mean absolute bias error (MABE), we inferred that there is a higher degree of temporal stability for SWC in wet conditions than in drier conditions on the two hillslopes. This demonstrates the feasibility of using the temporal stability of SWC to acquire mean SWC on karst hillslopes of southwestern China." said WANG Sheng, a doctor in ISA.

"The indirect method estimates mean SWC between the mean and the measurement value at a time-stable location, predicted mean SWC more precisely than the direct method (mean SWC directly measured at a time-stable location)," said WANG.

The researchers also found that soil texture, RFC, and elevation affect the pattern of SWC on the shrub hillslope and they recommended the use of the indirect method to acquire mean SWC values, when an allowable bias of 5 % for both MRD and SDRD can't be achieved. These results are expected to be useful for monitoring soil water dynamics on karst hillslopes, especially for restoration purposes.

This study was supported by the National Key Basic Research Program of China (2015CB452703), and the National Nature Science Foundation of China (41671287, 41301300 and 51379205). The study entitled "Temporal stability analysis of surface soil water content on two karst hillslopes in southwest China" has been published in Environmental Science and Pollution Research, details could be found at http://link.springer.com/article/10.1007/s11356-016-7686-x.