Hydrological modelling using raingauge- and radar-based estimators of areal rainfall

Three types of gridded rainfall estimator, based on raingauge and/or radar observations, are considered and their merits for hydrological modelling explored. Gridded multiquadric surface fitting techniques are developed to form raingauge-only and ‘raingauge-adjusted radar’ rainfall estimators. A third estimator is provided by the unadjusted radar data which comes in raw or Nimrod form. The latter is a post-processed radar product that aims to apply physically based corrections. These estimators are assessed first from a rainfall perspective, and then from a hydrological perspective by using them to provide rainfall inputs to hydrological models and comparing their simulated flows to observations. The PDM, a lumped conceptual rainfall-runoff model, and the Grid-to-Grid Model, a distributed grid-based runoff and routing model, are used for the hydrological assessment over two upland catchments in northwest England. Important insights are gained into the performance of the different rainfall estimators in assessing rainfall over space and their use in lumped and distributed hydrological models. The need for frequent and spatially varying gauge-adjustment of radar is identified as crucial for the weather radar products assessed.