Falling Lake Victoria water levels: Is climate a contributing factor?

Abstract

Recently, and perhaps most threatening, Lake Victoria water level has been receding at an alarming rate. A recent study suggested the possibility of the expanded hydroelectric power station in Uganda. However, since the lake receives 80% of its refill through direct rainfall and only 20% from the basin discharge, climatic contributions cannot be ignored, since the 80% water is directly dependant on it. It is therefore necessary to investigate climatic contribution to the declining Lake Victoria water level observed over a long period, i.e., 30 years. This contribution uses 30 years period anomalies for rainfall, river discharge and lake level changes of stations within Lake Victoria basin to analyse linear and cyclic trends of climate indicators in relation to Lake levels. Linear trend analysis using the Student's t test indicate a decreasing pattern in rainfall anomalies, with the slope being statistically similar to those of water levels at both Kisumu, Maziba and Jinja stations Climatic Change (for the same period of time , thus showing a strong correlation. On the other hand, cyclic trend analysis using Discrete Fourier Transform (DFT) shows cyclic period of water level to coincide with those of droughts and rainfall. The strong relationship between climatic indicators of drought and rainfall on one-hand and lake levels on the other hand signifies the need to incorporate climate information in predicting, monitoring and managing lake level changes.

The nature of rainfall in the main drainage sub-basins of Uganda

“…Raster maps of rainfall characteristics are prepared from regional data using the kriging interpolation method. Using rainfall data computed from equations put forward by Awange et al (2008), seasonal means, S m , were obtained by averaging the monthly totals, M t , for three months of a particular season, i.e. :…”

“…These were further categorized into the 30-year "normal", in accordance with the World Meteorological Organization (WMO) requirement (Awange et al 2008). Using rainfall data computed from equations (7) and (8), the normal precipitation (NP)-typically considered a 30-year mean-is obtained.…”

“…Using P n , a drought severity index (DSI) was determined by considering all observations which are less than 25% (first quartile) of the ranked historical records to be dry, while those which are more than 75% (third quartile) are considered wet. Awange et al (2008) illustrates severity classification as follows:…”

“…org/10.1080/02626667.2013.804188 variation on monthly, seasonal and annual time scales in order to manage water resources well. For example, 80% of the total catchments of Lake Victoria in East Africa rely on direct rainfall, while the remaining 20% comes from river and underground discharges (Awange 2008). Rainfall is also very important for the economic development, disaster management and hydrological planning of a country.…”

Modelling the water balance of Lake Victoria (East Africa) – Part 1: Observational analysis

“…According to earlier water balance studies, inflow from the basin accounts for 20 % of the total lake input, while direct precipitation on the lake accounts for 80 % (Awange et al, 2007a). River inflow was measured in different periods from the 1950s until the 1980s during an hydrometeorological survey initiated by the World Meteorological Organisation (WMO) (WMO, 1981).…”