Overview
Reforecasts (also sometimes called hindcasts) are sets of past forecasts that are computed retrospectively using the same (or as close as possible) model as the real-time forecast for a number of past dates. In CEMS-Flood hydrological reforecasts are generated for medium, extended and seasonal ranges using the same hydrological modelling chain as the operational forecasts and reanalysis datasets.
Compared with operational forecasts, reforecasts have two main advantages:
- they span a much longer time period, hence can describe better the interannual variability and contain larger sample of possible realisations useful to derive robust statistics
- they are generated retrospectively, using the same (or as close as possible) NWP model as the real-time forecast, hence containing the latest model development representative of the operational model
Hydrological reforecasts can be used for two main activities:
- to evaluate the skill of the forecast system, by comparing (proxy) observations with reforecasts for a set of past dates as long as possible
- to define climatological statistics consistent with the forecast modelling chain, which may have different biases than a reference run based on reanalysis or observations.