Recent ENSO influence on East African drought during rainy seasons through the synergistic use of satellite and reanalysis data

Abstract

This study identified a relationship between the El Nino-Southern Oscillation (ENSO) and East African drought during the two rainy seasons (i.e., short rain from October to December and long rain from March to May). ENSO shows a positive relationship with the East African short rain during the entire period analyzed (1949-2016). Meanwhile, a statistically significant relationship between ENSO and East African long rain appears only in a recent period (2000-2016), which is unprecedented in the past 50 years before the 2000s. The strengthened interannual relationship between ENSO and East African long rain is associated with distinguished Indian Ocean Walker cell in boreal spring, implying that their relationship could be affected by either multidecadal natural variability or anthropogenic forcing. Various satellite-based drought indices which consider vegetation health, land surface temperature, evapotranspiration, and precipitation with 1 km spatial resolution showed a robust relationship between ENSO and East African drought in the recent period (2000-2016) during the both rainy seasons. In the case studies of June 2005, August 2007, and November 2010, the anomalous wet condition in East Africa during the mature phase of El Nino became dry as La Nina developed in the following year, thereby a lagged response was observed in vegetation-related drought indices and long-term meteorological drought indices. Satellite-based high resolution (1 km) drought indices often showed heterogeneous drought patterns under the same drought condition from reanalysis data at coarse resolution (2.5 degrees), indicating the importance of spatiotemporally continuous high-resolution measurements for drought monitoring in East Africa. Consequently, the synergetic use of high resolution satellite observations and reanalysis data is crucial to provide the effective monitoring, assessment, and seasonal outlook of East African drought.