Sub-seasonal precipitation forecast skills over China during the boreal summer monsoon

Sub-seasonal precipitation forecasts during the boreal summer monsoon season are very valuable for flood and drought mitigation over China. Here, we evaluate the sub-seasonal precipitation forecast skills of 11 dynamic models from the Sub-seasonal to Seasonal (S2S) Prediction Project at various spatial and temporal scales. For ensemble mean forecasts, most models show significant correlations with observations at both grid and basin scales with lead time up to 2 weeks. When the lead time is beyond week-2, significant correlations are only observed over southeast and western China at the grid scale. Spatial aggregation helps improve week-3-4 average forecast skills at basin scales; significant correlations can be found for all hydroclimatic regions over China. For ensemble forecasts, most S2S models produce skilful forecasts at basin scale as measured by discrimination scores. Both the El Niño-Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO) have an impact on precipitation forecast skills at week-3-4. In particular, forecast skill improvement is most pronounced when the forecasts are initialized during active MJO center located in Maritime Continent (Phase 4~5). The results here will help inform the usefulness of sub-seasonal forecasts for hydrological modelling for drought and flood mitigation.