The 2010-2011 drought in the Horn of Africa in ECMWF reanalysis and seasonal forecast products

摘要

This study evaluates the use of European Centre for Medium-Range Weather Forecasts (ECMWF) products in monitoring and forecasting drought conditions during the recent 2010-2011 drought in the Horn of Africa (HoA). The region was affected by a precipitation deficit in both the October-December 2010 and March-May 2011 rainy seasons. These anomalies were captured by the ERA-Interim reanalysis (ERAI), despite its limitations in representing the March-May interannual variability. Soil moisture anomalies of ERAI also identified the onset of the drought condition early in October 2010 with a persistent drought still present in September 2011. This signal was also evident in normalized difference vegetation index (NDVI) remote sensing data. The precipitation deficit in October-December 2010 was associated with a strong La Ni?a event. The ECMWF seasonal forecasts for the October-December 2010 season predicted the La Ni?a event from June 2010 onwards. The forecasts also predicted a below-average October-December rainfall, from July 2010 onwards. The subsequent March-May rainfall anomaly was only captured by the new ECWMF seasonal forecast system in the forecasts starting in March 2011. Our analysis shows that a recent (since 1999) drying in the region during the March-May season is captured by the new ECMWF seasonal forecast system and is consistent with recently published results. The HoA region and its population are highly vulnerable to future droughts, thus global monitoring and forecasting of drought, such as that presented here, will become increasingly important in the future.