rivers, will render the dams inefficient and expensive in operation and with a short useful life, especially if landscapes in the watersheds of these dams are not well managed.
Figure 34: Current large dams by major sub-basin
Figure 35: Current and planned large dams by major sub-basin
2. The water security impacts of the Amazon droughts of 2005 and 2010
Recent unusual and extreme climatic events in the Amazon demonstrate the potential threat of such events to water security. Droughts were experienced in 1997, 2005 and 2010
while a severe flood occurred in 2009. The 1997 and 2010 droughts were caused by a combination of intensified ENSO events as a result of increased Pacific SST and high
Atlantic SST causing a northwest displacement of the inter-tropical convergence zone while
the 2005 drought is attributed to only a high Atlantic SST. Such drought events are projected to increase in frequency and severity for the Amazon region and the associated
forest loss through fire and degradation could accelerate climate change Zeng et al., 2008;
Lewis et al., 2011. The 2005 drought caused a simultaneous recession of the major tributaries of the Amazon river which led to a sharp fall in Amazon river runoff Tomasella
et al., 2011. Similar behaviour has been observed after the 2010 drought Marengo et al.,
2011. The impact of the 2005 and 1997 drought on floodplain communities was studied by
Tomasella, 2012 who found that - since all economic activities of these communities depend on the hydrological regime of the main stem - they were heavily impacted by the
droughts. The 2009 flood event caused mudslides and drove nearly 200,000 people from their homes Marengo et al., 2012 and resulted in record discharge being observed for the
Amazon river. Studies into these extreme events conclude that changes in the timing of
positive and negative rainfall anomalies puts river discharges from the northern and southern tributaries of the Amazon river in phase resulting in extreme positive and
negative discharges whereas in normal years, the timing is different attenuating the main-stem flood waves Tomasella, 2010; Marengo et al., 2012. Such unexpected and high
magnitude changes in water availability are therefore likely to have a great impact on
water security in the region.
3. Major changes in land use and their impacts
