Multidecadal Trends and Interannual Variability of Rainfall as Observed from Five Lowland Stations at Mt. Kilimanjaro, Tanzania

Abstract

Future rainfall dynamics in the Kilimanjaro region will mainly be influenced by both global climate and local land-cover change. An increase in rainfall is expected, but rising temperatures are also predicted for the ecosystem. In situ rainfall of five stations is analyzed to determine seasonal variability and multidecadal trends in the lowlands and lower elevations of the Kilimanjaro region. Monthly rainfall totals are obtained from the Tanzanian Meteorological Agency, from two mission stations, and from a sugar cane plantation. The datasets of the two mission stations cover time spans of 64 and 62 years, starting in 1940 and 1942, while rainfall data obtained from the Tanzanian Meteorological Agency and from the sugar cane plantation start in 1973 and 1974 and thus cover 40–41 years. In one out of five stations, a significant weak negative linear long-term trend in rainfall is observable, which is also evident in the other locations but is not significant. However, humid and dry decades are evident and seasonality has changed, especially during the long rains between March and May. El Niño–Southern Oscillation (ENSO) in combination with positive Indian Ocean dipole (IOD) leads to enhanced rainfall during the year of ENSO onset and the following year. During La Niña years, rainfall increases in the following year, while during the onset year rainfall patterns are more diverse. Positive IOD leads to enhanced rainfall amounts.

Seasonality of stable isotope composition of atmospheric water input at the southern slopes of Mt. Kilimanjaro, Tanzania

“…The years 2012 to 2014 differed considerably in amount and distribution of precipitation from normal years, as especially the year 2013–2014 was extremely wet. Shifts in seasonality and amount of precipitation are a commonly observed phenomenon in the Kilimanjaro region (e.g., Otte et al, ).…”

“…South‐easterly trade winds are produced by an ITCZ northwards of the equator, during (austral) winter (Duane et al, ). One distinct dry season ranges from June to September, and a second short dry season from January to February (e.g., Appelhans & Nauss, ; Hemp, ; Mölg, Hardy, Cullen, & Kaser, ; Otte et al, ). Interannual variability of the rainy seasons is caused by the El Niño Southern Oscillation and Indian Ocean Dipole (Otte et al, ).…”

“…One distinct dry season ranges from June to September, and a second short dry season from January to February (e.g., Appelhans & Nauss, ; Hemp, ; Mölg, Hardy, Cullen, & Kaser, ; Otte et al, ). Interannual variability of the rainy seasons is caused by the El Niño Southern Oscillation and Indian Ocean Dipole (Otte et al, ). Regarding total annual rainfall amounts, the northern slopes, on the lee side of the mountain, receive less rainfall (<1,000 mm) than the southern slopes (>2,500 mm; Hemp, ).…”

The influence of ENSO on the upper warm temperature anomaly formation associated with the March–May heavy rainfall events in Tanzania

“…Tanzania is the largest country in the EA Community located between 1-12 o S and 30-40 E (Figure 1). It has the highest point in Africa, the snow caped Mount Kilimanjaro about 5,895 m above sea level (Otte et al, 2016). It has a tropical climate but has regional variations from place to place in accordance with geographical location, altitude, relief and vegetation cover.…”

East Africa Rainfall Trends and Variability 1983–2015 Using Three Long-Term Satellite Products

“…This is a common practice in case of rain gauge time series to eliminate, or at least reduce, the non-climatic noise caused by station relocation, changes in instruments, etc., which can affect the trends introducing spurious signals not produced by the real climate variability [30][31][32]. The datasets exploited in the present work come all from a reprocessing activity granting for the use of an unvaried version of the retrieval algorithms over the time.…”