Causal pathways linking different flavours of ENSO with the Greater Horn of Africa short rains

Abstract

There is a strong association between canonical El Niño and a wet Greater Horn of Africa (GHA) short rains. However, the link with Modoki El Niño events appears to be significantly weaker. In order to understand this, we present an analysis of observational data and idealised climate model experiments. Idealised atmospheric simulations isolate the direct influence of Pacific heating on the GHA and reveal that neither the longitudinal position nor the observed weaker magnitude of Modoki Pacific heating anomalies can explain the difference in teleconnections. The direct effect of canonical or Modoki Pacific heating patterns on the GHA is similar and neither reproduces the structure of the full GHA teleconnection: they both generate a wet‐dry dipole over the GHA instead of large‐scale single‐signed wet anomalies. Our results indicate that the strong canonical ENSO influence on GHA is indirect, mediated through its strong relationship with the Indian Ocean Dipole (IOD). By contrast, Modoki ENSO is uncorrelated with the IOD, resulting in weak teleconnection to GHA. Understanding these differences aids seasonal forecast interpretation, whilst their representation in models is likely a prerequisite for making accurate projections of changes in extremes over the GHA and beyond.

Tropical Indo-Pacific SST influences on vegetation variability in eastern Africa

“…This offset response is consistent with the opposite impact between Indian Ocean Basin-wide mode (IOBM) and ENSO on seasonal rainfall variability over Africa discussed in previous studies 37 . The IOD is another primary climate factor, which can affect rainfall and vegetation variability over eastern Africa 2,[37][38][39] , but the IOD impact to eastern Africa peaks in September-November [SON(0)] (Fig. S6).…”

Skilful long‐lead hybrid predictions of the East African short‐rains season

“…The CHIRPS data are very high resolution (0.05 × 0.05 ) daily data. CHIRPS has been widely used for climate study and prediction in East Africa including by Bahaga et al (2019), Peng et al (2020), andMacleod et al (2021). The CHIRPS rainfall performed very well when compared with in situ observations, likely because of its direct inclusion of rain gauge data and microwave images during calibration (Kimani et al, 2017).For this study we generated seasonal-average data for the short-rains (October-December, OND) season.…”

Future Changes in the Indian Ocean Walker Circulation and Links to Kenyan Rainfall

“…The IOWC, and the zonal SST pattern known as the Indian Ocean Dipole (IOD) which can perturb the IOWC when active, are important influences on the hydroclimate of East Africa (Black, 2005; Nicholson, 2017). The IOD links East Africa to wider tropical interannual variability via non‐stationary teleconnections to the El Niño Southern Oscillation (ENSO; MacLeod et al., 2020; Nicholson, 2015). The climatological overturning cell features ascent over the Maritime Continent and descent over East Africa from September to March (Zhao & Cook, 2021), which is a contributor to the relative aridity of Kenya despite its location on the equator (King et al., 2020; Nicholson, 2017).…”