Estimating spatial mean available water storage in a small catchment of the hilly area of the Loess Plateau

The complex topography of the hilly area of the Loess Plateau(especially gullies)leads to the difficulty of calculating watershed-scale available water storage (AWS). Based on soil moisture datasets from 2010-2012 in the Yuanzegou catchment of the Loess Plateau,this study attempted to estimate AWS of hillslopes,gullies and watershed from one single sampling location on the hillslopes for each layer,by coupling time stability analysis with observation operators. The AWS datasets in 2010 and 2011 were used for time stability analysis,development of observation operators and estimation of AWS of hillslopes,gullies and catchment. The AWS datasets in 2012 were used for validation. The results show that the AWS of hillslopes can be accurately estimated through that of one single hillslope time-stable location for each depth. Furthermore,the AWS of gullies and catchment are also well estimated from the hillslope time-stable location by using the method of observation operators. The validation analysis indicates that the time-stable location and the developed observation operators for various depths are temporally robust.