Multiple studies demonstrate that inverse distance weighting (IDW) is an effective and widely used method for interpolating rainfall data from external stations across a watershed, particularly when enhanced with elevation or adapted for sparse networks.
The retrieved literature contains multiple papers evaluating spatial interpolation methods for rainfall in watersheds, with papers [5], [6], [9], and [10] directly supporting the use of inverse distance weighting (IDW) for this purpose. While other papers discuss geostatistical alternatives like kriging, none refute IDW as a viable interpolation method, leading to a supported verdict.