Post
by come-along.nl » Tue Apr 23, 2013 12:19 pm
Okavango flooding to be moderate in 2013
By Piotr Wolski
As a result of the below average rainfall in the Okavango catchment area and the Angolan highlands, flooding of the Okavango Delta is expected to be moderate this year. The rainy season of 2012/2013 was poor. In Maun, recorded rainfall was in the order of 300-400 mm (depending on location), which is lower than the long term average of 460 mm per year, and considerably lower than rainfall in the recent years (500-900mm).Rainfall in the Okavango River catchment was also lower than in the recent years. Measurements using satellites indicate that this year's rainfall in the Angolan highlands amounted to approximately 600 mm, while during the last four years rainfall there exceeded 750 mm per year. As a result of the low Angolan rainfall, the flow of the Okavango River is moderate. At Mohembo, the inflow since November till now amounted to only 5 500 million cubic meters, and we estimate that the total amount of inflow for this year's flood - that is till the end of October - will be around 8700 million cubic meters. This is not much compared to the flood of 2010/2011 when the total inflow was 13 500 million cubic meters but it is larger than the lowest recorded flows in 1996, when total inflow was a meagre 5 000 million cubic meters. A flood of similar magnitude to this year's one was recorded the last time in 2005. Since 1934, approximately 4 out of every 10 floods were larger than the one expected this year. The flood is approaching the distal parts of the Delta. In Maun, water levels rose strongly in January, following a rainfall event when 70-100 mm of rain fell within a day. At this stage, however, water has been dropping since mid-March and is expected to continue dropping at least in the next couple of weeks. It is estimated that once the flood arrives at Maun, water will be rising till the first week of September, but the maximum level reached will be at least 0.75 m lower than that recorded last year. In spite of the moderate Thamalakane flood, it is likely that the Boteti River will be flowing along its entire length. Similar moderate flooding is expected to occur in the Kunyere River (Toteng). This flood will re-supply Lake Ngami, which remains extensively flooded even now, so it is highly unlikely for the lake to dry during the next couple of years.
*Professor Piotr Wolski is a hydrologist at the University of Botswana's Okavango Research Institute in Maun.
