Dominant atmospheric circulation patterns associated with abnormal rainfall events over Rwanda, East Africa

Abstract

ABSTRACT:The study investigated the dominant atmospheric circulation patterns associated with abnormal rainfall over Rwanda during the March-May (MAM) rainfall season in 1981-2010. The data sets used in this study include: rainfall, wind, sea surface temperature (SST), and humidity. Correlation and composite analysis and Percent of Normal Index (PNI) were deployed in this study. In the wet years (1987, 1988, and 1998), the country was dominated by moisture convergence, which is in line with wind anomalies that exhibits strong westerly winds from the Atlantic Ocean and southeasterly winds originated from the Indian Ocean. These winds carry moist air mass passing over Congo to the study area, leading to wet events. On the other hand, easterly winds were noted over the study area during the dry years (1984, 2000, 2007, and 2008). The observed wet years coincided with the El Niño events, while the dry years are noted during the La Niña episodes. The dry years exhibited a wide spread of moisture divergence anomaly at the low level and were characterized by the sinking motion as opposed to the wet years with the rising motion. The anomalies of velocity potential/divergence further showed that the wet (dry) years were characterized by convergence (divergence) at the low level. The results also show that there exists a low positive correlation between mean MAM rainfall and SST over the Indian Ocean, which shows minimum influence of the Ocean. On the other hand, it was noted that rainfall amounts is significantly correlated at 95% confidence level with the elevation (altitude) of a given station. This study improves the understanding of the occurrence of wet and dry events in Rwanda, which is helpful in future monitoring of these events.

Spatial and temporal patterns of drought in Zambia

“…In this study, the standardized precipitation index (SPI) was used to explore the patterns of drought because of its convenience in categorizing them (McKee et al, 1993;Hayes et al, 2011;Ngarukiyimana et al, 2017). SPI is based on precipitation data only, and it runs a comparative analysis of annual average precipitation and transforms the data to a normal distribution in order to avoid errors.…”

Comparative Analysis of the Performance of Satellite‐Based Rainfall Products Over Various Topographical Unities in Central East Africa: Case of Burundi

“…During recent years, the JF is experiencing either dry conditions or abnormal rains disrupting the harvest of Season “A” crops especially in the plateau (Bisore, ; PNUD, ). These changes can be linked to the climate variability and external drivers affecting East Africa such as El Niño Southern Oscillation, Indian Ocean Dipole and Mascarene High (Ogwang, Chen, et al, ; Ogwang, Ongoma, et al, ; Ngarukiyimana et al, ).…”

“…During that season most of the regions of the country register very low or no rainfall. In East Africa, the bimodal rain patterns and the dry seasons are linked to the double passage of the Intertropical Convergence Zone (ITCZ) as stated by some scholars (Ogwang, Chen, et al, ; Ogwang, Ongoma, et al, ; Ongoma et al, ; Ngarukiyimana et al, ). However, although the rainfall variability is linked to the general atmospheric circulation and the passage of ITCZ, many other factors affect the climatology of Burundi.…”

“…Burundi generally experiences two wet seasons per year. According to research carried out by many scientists, it has been found that most of east African countries benefit bimodal rainfall patterns each year (Ayugi et al, ; Ngarukiyimana et al, ; Nkunzimana et al, ).…”

“…The evaluation has been conducted for 17 years ranging from 2000 to 2016. The choice of studying the period 2000–2016 is motivated by the fact that this period is found to record more extreme weather events not only over Burundi but also over East Africa in general (Ongoma et al, ; Chang'a et al, ; Ngarukiyimana et al, ; Nkunzimana et al, ). Therefore, an evaluation on daily scale for this period is of more concern.…”