Assessing seasonal climate forecasts over Africa to support decision-making

Recent drought events like in the 2011 Horn of Africa and the ongoing drought in California have an enormous impact on nature and society. Reliable seasonal weather outlooks are critical for drought management and other applications like, crop modelling, flood forecasting and planning of reservoir operation, and would help reduce the potential economic damage from extremes as well as help optimize crop yields during more normal weather years from improved agricultural management. However, most seasonal forecasts are limited by low spatial and temporal model resolutions. The newly released North American Multi-Model Ensemble phase 2 (NMME-2), provides subseasonal forecast that increase the temporal resolution from monthly to daily, enabling subseasonal forecasting for end-user applications that rely on a daily temporal resolution. In this study we give an overview of the current status of the NMME subseasonal forecasts ensembles, their skill over the African continent and the forecast skill of the ensembles for applications related to agriculture and hydrology. We show that the NMME-2 subseasonal forecasts are significantly skilful for both precipitation and 2 m air temperature for large parts of Africa. The precipitation forecasts are skilful up to a lead time of two months, while temperature anomaly forecasts have a significant skill beyond the three months lead for most of Africa. Potential applications that would benefit from the new NMME-2 ensemble were studied in more detail for West Africa. We show that the models have a significant skill in forecasting the onset of the annual rain season in West Africa, and thereby the start of the growing season. Additionally, the models have a significant forecast skill to predict the onset and peak of the high flow season for most parts of West Africa. The low uncertainty in the forecasts compared to the observed anomalies indicates that local stakeholders will benefit from the high temporal resolution that the NMME-2 provides. Results encourage future research into the potential of the new subseasonal NMME-2 forecast ensemble to forecast more specific end-user applications and climate services, which require skilful high temporal resolution forecasts.