Intra‐seasonal variability over the northeastern highlands of Tanzania

Abstract

ABSTRACT:The intra-seasonal variability of rainfall over the northeastern Highlands (NEH) of Tanzania during the March, April, May (MAM) rainfall season and associated circulation anomalies have been studied for selected wet and dry years. Station rainfall data were used to extract the onset, peak, and cessation dates of the rainfall season and National Center for Atmospheric Research/National Center for Environmental Prediction (NCEP/NCAR) data were used to study the atmospheric circulation features associated with the intra-seasonal variability. It was found that the anomalously wet MAM seasons over the NEH of Tanzania tend to result from an earlier onset of the rains and a late cessation and thus, a longer-than-average rainfall season, whereas, dry years were characterized by a shorter-than-average duration of the rains. The moisture flux plots indicate that the composite wet MAM seasons were associated with advection of moisture from both the Indian Ocean and the Congo Basin. For the dry MAM seasons, a cyclonic anomaly off the Somali coast leads to southerly moisture flux anomalies over Kenya and westerly anomalies over the Indian Ocean which, together with easterly moisture flux anomalies over the Congo Basin, act to divert and transport low-level moisture away from Tanzania.Lag correlations between time series of moisture over the Congo (0-8°S; 20-29°E) and MAM rainfall over the NEH indicated a phase locking of the two variables that occurred during the years with larger rainfall anomalies. A significant correlation was observed two months before the onset of the rainfall season in January that indicates that some predictability of the MAM seasonal rainfall total based on the Congo Basin zonal wind may exist. However, given the constraints of the available data and the regional atmospheric circulation, it is possible that additional predictors may be required when developing forecast models of the MAM seasonal rainfall.

Climate and climatic variability of rainfall over eastern Africa

“…During the long rains seasonal rainfall is only moderately correlated with those statistics but is strongly correlated with the number of extreme wet events [Pohl and Camberlin, 2006a]. Farther south, in Tanzania, rainfall during the long rains is correlated with both the onset and end and thus with season length [Kijazi and Reason, 2012]. Camberlin and Okoola [2003] found that a late onset of the long rains is correlated with positive sea level pressure over the Indian Ocean and negative sea level pressure over the South Atlantic.…”

“…During the long rains seasonal rainfall is only moderately correlated with those statistics but is strongly correlated with the number of extreme wet events [ Pohl and Camberlin , ]. Farther south, in Tanzania, rainfall during the long rains is correlated with both the onset and end and thus with season length [ Kijazi and Reason , ].…”

“…The opposite pressure pattern prevails during wet spells in the east, when easterly anomalies advect moisture from the Indian Ocean. Kijazi and Reason [2012] found that farther south, over Tanzania, the region received moisture from both the Congo Basin and the Indian Ocean during wet spells.…”

Assessing Prone Areas to Heavy Rainfall and the Impaction of the Upper Warm Temperature Anomaly during March–May Rainfall Season in Tanzania

“…Kijazi and Reason [13] found that increased fetch of lowlevel moisture flux anomalies from the Congo basin and the tropical Indian Ocean can result in the increase in MAM rainfall over Tanzania. Meanwhile, Nicholson [14][15][16] noted that the intensity and location of rainfall over the eastern Africa are strongly associated with the meridianally aligned ITCZ into which the humid south Atlantic air-masses converge with the Indian Ocean trade winds.…”

Use of El Niño–Southern Oscillation related seasonal precipitation predictability in developing regions for potential societal benefit

“…Research collaborations between other areas of skill similar to southern Africa but with varying human development levels have, for example, recently taken place. Funded studies of rainfall variability over respectively Kenya (Gamoyo et al, 2015) and Tanzania (Kijazi and Reason, 2012) involved scientists from both these countries in east equatorial Africa and southern Africa. Moreover, although northern and northeastern Brazil have seasonal forecast skill levels statistically different from southern Africa but with similar HDI values, important funded research collaboration resulted in an improved understanding of the climate system affecting both regions (Grimm and Reason, 2011;.…”