Therefore, the selection of error estimation methods of P product should consider the application purpose. For example, when the study refers to only one hydrological variable with sufficient measure values for application of statistical methods, they are best selection due to low data uncertainties, such as analysis in spatio/temporal changes of precipitation and analysis of extreme precipitation. Because the high accuracy of precipitation only can meet requirements of these kinds of analysis. However, when two or more hydrological variables are involved in analysis of hydrological processes, these two kinds of methods should be considered for guaranteeing the accuracy of HDPs, i.e. the optimal data error and the highest budget closure accuracy.