Lake Victoria Rising Water Levels

Heavy rainfall caused a rise in water levels above historical records in Lake Victoria, the biggest trans-boundary freshwater lake in Africa, from late 2019 to mid-2020. The rising water levels caused significant flooding on the small island and shoreline communities, displacing over 200,000 people in Kenya, Uganda, and Tanzania.

Lake Victoria Background

Lake Victoria, locally known as Lolwe, Sango, or “The Eye of the Rhino,” covers an area of 68,800 km2 ( Lake Victoria Basin Commission ). Three countries share its surface waters: Tanzania, Kenya, and Uganda. The lake is fed by  23 rivers , of which Kagera is the largest; it runs through Rwanda and Burundi before emptying into the lake.

 The Lake Victoria basin  has a drainage area of 183,000 square km ( Lake Victoria Basin Commission ) which covers Rwanda, Burundi, Uganda, Kenya, and Tanzania. Lake Victoria is the source of the White (Victoria) Nile, which flows north to meet the Blue Nile in Sudan, forming the Nile River in northern Sudan and Egypt. This outflow into the White Nile river is controlled by two dams: Kiira and Nalubale dams (formerly known as Owen dams) in Jinja. The East African countries of Rwanda, Burundi, Uganda, Kenya, and Tanzania rely on the hydroelectric power generated by these dams, as well as on the lake for fishing, water, and irrigation.

Rainfall Anomaly

Most of the recharge into Lake Victoria is from rainfall. The amount of regional rainfall, therefore, regulates the water levels in the lake. We applied NASA’s  Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG)  dataset, which provides global monthly rainfall at ~10 km spatial resolution, to show yearly seasonal rainfall patterns and trends over this region.

Figure 1 (select the layers, click the swipe icon and swipe for comparison) shows changes in yearly seasonal rainfall, derived using GPM IMERG, over Lake Victoria basin in 2019 compared to an 11-year seasonal average from 2008-2018. In 2019, both the wet months from September to November (SON) and dry months from December to February (DJF) received relatively higher rainfall than in the previous 10 years. The IMERG yearly seasonal rainfall trend from 2008 to 2020 (Figure 2A) shows clear wet and dry seasonal patterns in the basin. The station level data, located at a nearby station Kisumu in Kenya, shows an increase in precipitation above normal starting from October 2019 through October 2020 (present) except for June 2020 (Figure 2B, ). The station data can be obtained from the United States Department of Agriculture (USDA)  WMO Station Explorer  (station locations are shown in Figure 1 and 3).

Figure 1: Seasonal monthly average rainfall over Lake Victoria in the December-February (DJF), March - May (MAM), June - August (JJA), September - November (SON) of 2019 compared to seasonal monthly average rainfall from 2008 to 2018. Yellow dots indicate  WMO Station  locations.

Increased Water Level

Responding to the increased runoff during 2019-2020, the water level in Lake Victoria rose to a new record level of 13.42 meter in May 2020, surpassing the 13.41 meter mark recorded in 1964 (Lake Victoria Basin Commission). The  Gravity Recovery and Climate Experiment Follow On (GRACE-FO)  monthly water storage data at 0.5 degree spatial resolution were used to detect changes in the amount of water in the lake. The time-series graph derived from GRACE-FO shows rising water storage in the lake environs from 2003 to 2020 (Figures 2C) and water height variations from 1992 to 2020 (Figure 2D). The increase in water mass through time can be observed using the  State of the Ocean  interface.

A) Seasonal Rainfall Profiles

Yearly seasonal average monthly rainfall profiles over Lake Victoria basin derived from GPM IMERG Final monthly data from 2008-2020.

B) Monthly Rainfall at Kisumu Station in Kenya

Monthly precipitation in 2019 and 2020 compared to normal precipitation (1961-1990) at Kisumu Station in Kenya.

C) Water Storage Anomalies Measured as Liquid Water Equivalent Thickness

Profile of monthly global water storage anomalies relative to a 2004-2009 base period mean, measured as liquid water equivalent thickness (cm) from GRACE and GRACE-FO over Lake Victoria from 2002 to 2020.

D) Historical Lake Water Variations

Historical water height variations in Lake Victoria acquired from USDA's Global Reservoirs and Lakes Monitor (G-REALM). The time series graph is constructed using near-real- time data from the Jason-3 mission, and archive data from the Jason-2/OSTM, Jason-1, TOPEX/Poseidon, and ENVISAT missions.

Figure 2: Time series of A) seasonal rainfall profiles from GPM IMERG, B) monthly precipitation in 2019 and 2020 compared to normal precipitation at Kisumu Station in Kenya obtained from United States Department of Agriculture (USDA) WMO  Station Explorer , C) water storage from  GRACE-FO , and D) historical lake water height variations from TOPEX, Jason-1-3 from USDA's  Global Reservoirs and Lakes Monitor (G-REALM) .

 NASA’s Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (FLDAS)  dataset also provides monthly anomaly of rainfall flux and runoff globally at 0.1 degree spatial resolution. FLDAS data are produced using the Noah Land Surface Model (LSM). FLDAS only simulates soil moisture and runoff over land area, and does not calculate a water balance over lakes. The FLDAS meteorological forcing, however, does provide rainfall data over both land and lake areas. Therefore, the runoff anomaly from FLDAS will not show any values over the lake, while the rainfall flux from FLDAS will. The anomaly of rainfall flux from October 2019 to June 2020 further reinforces the wetter anomalies observed in the Victoria basin (Figure 3).

Vulnerable Population

The rising water levels have caused significant flooding on the small island and shoreline communities  displacing over 200,000 people  in Kenya, Uganda and Tanzania.  Population  data from the NASA Socioeconomic Data and Applications Center (SEDAC) show many densely populated islands in the lake (Figure 3: SEDAC population layer). Small islands, such as Ringiti, Remba, and Migingo in Kenya, and Masolya Island in Uganda, were submerged due to high waters (Figure 3: island layer). Residents of these islands were displaced to either the mainland or nearby islands at higher elevations.  Road  and  building  layers (Figure 3: road and building layer) show built-up areas within the 300-meter protected zone surrounding the lake (Figure 3: buffer layer). As the water level in the lake increases, crops (Figure 3: cropland layer) and infrastructures have been destroyed and these  low  -  lying  shoreline communities within the protected zone have been severely affected.

Disruption in Livelihood

For many of the coastal communities around the lake, fishing is a large part of their livelihood. The fishing industry in Homa Bay County, Kenya, for example, has already been negatively affected by this event. It has been hampered by the effect of the rising water, particularly the submersion of shoreline markets.

The surrounding  cities  at Ggaba and Port Bell in the  Kampala  metro area in Uganda were submerged by  floodwater  (Figure 3: cities layer). Popular beaches such as Ggaba Beach, K.K Beach, Miami Beach were  under water . Dislodged floating vegetation has even  clogged intakes at the power-generating dams .

Ecosystem Imbalance

Lake Victoria is one of the biggest lakes situated between the Eastern and Western Rift Valleys (Figure 3: biodiversity layer). The great Rift Valleys are the hotspots of biodiversity and home for around  800 species of cichlid fish  and a breeding ground for birds. The  shoreline  marshy area of Lake Victoria is a habitat for hippopotamuses and crocodiles. The Lake Victoria islands, notably the Ssese Islands in the northwest part of the lake, provide home to many key species: hippos, monkeys and exotic Sitatunga antelopes. The high water levels in Lake Victoria flooded the surrounding swampy habitat of hippopotamuses, which forced them to feed and breed near residential areas. This shift brought them into closer contact with people,  causing a human-wildlife conflict. 

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