Mixed‐Station Extension of Monthly Streamflow Records

Monthly streamflow records at a site are sometimes extended by exploiting interstation correlation of streamflow, often through simple linear regression with a base station having a long‐term record. An approach is presented which selects a base station from among several in a region for filling in missing data. It differs from traditional approaches in that different stations can be selected as the base station to fill in different values. The approach also provides a decision rule for using only flow values from the same month or all flow values in developing the extension equation used for estimating a particular missing value. A previously presented extension equation to minimize variance bias of the flows estimated at the short‐record station is shown to be applicable to this technique. The possibility of using this extension equations to adjust the results of multiple regression in order to account for variance reduction is also suggested.