Exploration of the ENSO-Sahel Relationship on Intraseasonal to Interannual Timescales and its Relevance to Local Climate Services

Previous studies have identified and elucidated a relationship between the El Niño Southern Oscillation (ENSO) climate mode in the Eastern Tropical Pacific and rainfall in the West African Sahel, the semi-arid grassland which sits directly south of the Sahara desert and exhibits large variability on a number of timescales. In particular, during warm events (El Niño), the Sahel is expected to be anomalously dry while during cold events (La Niña), rainfall anomalies are of the opposite sign and the region tends to be wetter than normal. However, the seasonal total of rainfall that occurs in West Africa during an ENSO event cannot simply be understood in terms of thinking of the magnitude and warm or cold nature of the event itself. For example, during the extraordinary 1997 El Niño event, the Sahel was only modestly dry, and some of the strongest La Niña years (e.g. 1973 & 1975) were not the wettest seasons for the Sahel during the 20th Century. It is with inconsistencies such as these in mind that the Sahel's behavior during ENSO events is studied with a diagnostic framework, utilizing newly available high-resolution observations such as the CHIRPS dataset. Specifically, we complete this study with the following objectives, to study whether the precipitation response in the Sahel is different when El Niño is growing versus when it is on the decline, and to understand whether the state of the Tropical Atlantic can modulate the ENSO teleconnection to the Sahel. Results from this work have particular relevance for informing seasonal forecasting applications as these forecasts are primarily made using the current state of ENSO to inform local experts on the probability of having a normal, above normal, or below normal rainfall season. An example of how the increased knowledge of ENSO's effects on Sahel rainfall may be used will be discussed by detailing current efforts of the Agence Nationale de l'Aviation Civile et de la Météorologie (ANACIM) du Sénégal, host to the lead author's visit in country to work on delivering climate information and build resilience to climate variability locally.