El Niño Retrospective: Senegal, Part 3
This post is the third in a series of three articles by graduate student Catherine Pomposi about the 2015 El Niño forecast and its climate impacts in Senegal, as well current efforts to better understand climate in the Sahel.
Looking back on the 2015, El Niño and West African Rainy Season
As the rainy season progressed, Senegal’s Agence Nationale de l’Aviation Civile et de la Météorologie (ANACIM) continued to issue forecast updates to the communities in which they work. Now that the season (July-September 2015) is over, scientists are quantifying the accuracy and usefulness of the forecast itself.
One way in which ANACIM and partner organizations test the application of the forecast is through experimental crop beds in some of the local villages, where they compare yields from beds where the scientific seasonal forecast information was and wasn’t applied in management decisions. This serves as a good research tool and one way to show how climate information can be meaningful to the sectors most sensitive to climate variability.
Another important analysis is to compare how much rain fell to what was expected by scientists (see my first post) before the season began. Back in June, many signs were pointing toward an El Niño event developing, which usually translates to dry conditions in West Africa. In fact, the El Niño event not only developed, it continued to gain strength and is now considered one of, if not the strongest, events since 1950. So, we might be surprised to see that a map of July-September precipitation anomalies (i.e. the rainfall deviations from the long-term average) looks like this:
If we focus on the Sahel region, then we see much of the region exhibiting above-normal precipitation. Why might the Sahel have been wetter than normal, given the El Niño event? The climate system is large and complex and nothing operates in isolation. Other ocean basins have also been shown to affect the Sahel, so perhaps their contributions helped to maintain a wet signature rather than a dry. One possibility is that the warmer-than-usual SSTs directly off the west coast of Africa (see map below) helped to bring increased moisture supply to the continent.
The climate system is large and complex and nothing operates in isolation.
Back in June, it was difficult to forecast how these SST anomalies were going to develop. The June SST map in my first post showed equal areas of warm and cool anomalies around the same region. It was the warm water, however, that persisted from July-September, likely helping alleviate some of the dry conditions we expected from El Niño. But without the help of controlled model experiments, it is difficult to make the conclusion that this warming in the Atlantic saved the region from an otherwise drier fate for the 2015 rainy season.
Visiting Senegal motivates me to continue to study rainfall patterns in this semi-arid region. Indeed, I have tailored some of my research questions based on my time spent in the country. I have a better appreciation and understanding of the difficult climate conditions that exist in this semi-arid land than I would have received simply from reading climate textbooks. My trips have also allowed for me to witness first-hand the power of climate information and its influence on lives and livelihoods, as well as the ability of science to truly serve society.
This year’s rainy season is a great example of the complexity of the climate system and how competing influences might work together to give us an unexpected outcome. As I continue my studies of the monsoon from far away in NYC, I’ll be trying to disentangle how the major ocean basins work together to force changes in the atmosphere that then translate to changing precipitation over land.
