TITLE:
Convective Rainfall in Lake Victoria Watershed and Adjacent Equatorial Africa
AUTHORS:
Felipe Vemado, Augusto José Pereira Filho
KEYWORDS:
Lake Victory, Precipitation, Deep Convection, Diurnal Cycle, CMORPH
JOURNAL NAME:
Atmospheric and Climate Sciences,
Vol.11 No.3,
May
19,
2021
ABSTRACT: An integrated satellite precipitation estimation
dataset, namely, the Climate Prediction Center morphing method (CMORPH), was
used to analyze precipitation regimes across Equatorial Africa between 3°S - 1°N and 24°E - 42°E from 2000 to 2014. This region includes the
Rift Valley, part of the Congo Forest, and the Lake Victoria (LV) basin, the
second largest lake in the area of the world. Hovmöller diagrams were obtained
for all organized convective systems to estimate their spans, duration, and
phase speeds. The analysis included 33,189 episodes of westward propagating
convective systems. Within the study area, lake and land breezes tend to
trigger convection and precipitation over LV as well as mountain-valley
circulation trigger thunderstorms over the mountains east of LV and western
Rift Valley. The statistics of convective systems streaks on longitude-time
diagrams were obtained for yearly frequencies of starting and ending longitudes
and times among other morphologic variables. Results indicate organized
precipitation episodes tend to move westward across Rift valley and Congo
forest with an average phase speed of 10.3 m·s-1. More than 50% of them are triggered over LV and propagate more than 600
km at an average phase speed of 12.1 m·s-1. These convective
systems tend to produce high rainfall rates hundreds of kilometers away into
the Congo Forest. Half of all episodes of organized convection analyzed have
phase speeds between 8 m·s-1 and 16 m·s-1, lasting 8 hr to 16 hr. Most precipitating systems start east of LV and
west of Rift Valley in the afternoon to early morning and propagates less than
400 km. Finally, hourly precipitation accumulation and lightning density
analysis indicate three preferable regions for convective initiation: 1) The
mountain range east of LV; 2) Midwest of LV, and; 3) The Congo Forest mountain
range.