Pacific sea surface temperature linkages with Tanzania's multi‐season drying trends

Abstract

During 1999–2014, Tanzania experienced below average precipitation in two important seasons: December to February (DJF) in the south and during March to June (MAMJ) in the northeast. We explore DJF and MAMJ precipitation in the areas with drying trends and examine their relationships with anomalous sea surface temperatures (SSTs) in the Indo‐Pacific and corresponding circulation patterns. At seasonal time scales, precipitation in DJF and MAMJ trend areas appears inversely related to diabatic forcing in the equatorial Pacific. Dominant influence for droughts in DJF is eastern Pacific SST while for droughts in MAMJ it is West Pacific SST. A bivariate regression model with West Pacific and Niño3.4 region SST as predictors is found to recreate multidecadal DJF variability after the 1950s and the extreme drying in MAMJ during the 2000s. The regression model coefficients also indicate differential eastern versus western Pacific forcing for DJF versus MAMJ. Thus, we suggest that recent La Niña‐like conditions, characterized by an enhanced Pacific SST gradient due to cooling in the eastern Pacific and warming in the western Pacific, played a substantial role in Tanzania's recent multi‐season drying trends. SST change scenarios (difference between 2023–2037 and 2000–2014 means) based on CMIP5 projections and observed trends illustrate the uncertainty of future precipitation outcomes, as well as the potential implications of contrasting linkages to eastern versus western Pacific SSTs. These scenarios are mainly optimistic for the DJF southern Tanzania trend area, because it appears dominated by Niño3.4 cooling at both seasonal and decadal time scales. Conversely, our scenarios are quite pessimistic for the MAMJ northeastern Tanzania trend area, because we find a dominant negative influence of warming West Pacific SST.

Using seasonal rainfall clusters to explain the interannual variability of the rain belt over the Greater Horn of Africa

“…Harrison et al . (2019) found strong correlations between drought conditions in southern Tanzania during the December–February season and La Niña‐like conditions in the equatorial Pacific at interannual and decadal time scales. The authors explain this teleconnection by both shifts in the tropical Walker circulations and modulations of the Rossby wave train in the southern hemisphere extratropics.…”

“…Due to a recent abrupt decline of the Long Rains causing devastating droughts, they have been in the focus of many previous studies (e.g., Funk, 2011; Williams and Funk, 2011; Lyon and DeWitt, 2012; Liebmann et al ., 2014; Funk et al ., 2018; Funk et al ., 2019; Harrison et al ., 2019). Even though details vary, the decline has been attributed to sea surface temperature (SST) patterns in the Indo‐Pacific warm pool and related changes in the Walker cells.…”

Sensitivity of projected climate impacts to climate model weighting: multi-sector analysis in eastern Africa

“…Accordingly, for the variables temperature (T) and precipitation (P), we define indicators of (i) mean state, including seasonality; (ii) variability, including both the magnitude and the dominant driving process, in this case, simplified to the teleconnection with the El Niño Southern Oscillation (ENSO) that exerts a dominant influence on the region (e.g. Kolusu et al 2019;Harrison et al 2019); and (iii) change; specifically recent multi-decadal trends when anthropogenic climate change is most pronounced. This is consistent with the recommendations for adaptation-focussed model evaluation of Nissan et al (2019).…”

Causes of the Widespread 2019–2020 Australian Bushfire Season

“…In addition, natural climatic variability has been linked to seasonal‐decadal long droughts in various regions (Forootan et al, 2019; Kiem & Franks, 2004). Furthermore, sea surface temperature alterations are also claimed to have strong associations with regional droughts (Harrison et al, 2019; Wu & Kinter, 2009) which further governs the spread of bushfires (Russo et al, 2017).…”