The Cascade’s Impacts Going into the Future

The original cascade has since been modified to exclude the Mengsong dam, and has called for a smaller Ganlanba dam, which is currently being planned with basic preparatory work begun. This, along with the impending completion of the Nuozhadu dam later this year, means that the cascade is very nearly complete. The question, therefore, is no longer what should be done about possible future projects of the original plan, but rather how the impacts of the cascade will be dealt with going into the future.

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As stated in Rasanen et al (2012), the most significant impacts of the dam will be seen over the next decade, while the impacts of the climate change will be growing throughout the next half-century.

According to the fifth assessment report from the IPCC, over the past 30-50 years climate change in the lower Mekong basin has manifested through: an increase in

temperature, an increase in rainfall in the wet season and decreases in the dry season, intensified flood and drought events, and sea-level rise. In addition, according to the MRC (2009), agricultural output has noticeably been impacted by intensified floods and droughts, causing an almost 90% loss in rice production in Cambodia from 1996-2001.

Vietnam and Cambodia are the two countries most vulnerable to impacts on fisheries due to climate change, with sea level rise and decreased sediment in Vietnam and altered flood regimes in Cambodia (especially the Tonle Sap lake) (IPCC 2014). Studies on climate change’s predicted impact to the region come to the following common conclusions: increased temperature and annual precipitation; increased depth and duration of flood in the Mekong Delta (Vietnam) and Cambodia floodplain; prolonged agricultural drought in the south and east of the basin; and sea-level rise and salinity intrusion in the Mekong delta (IPCC 2014). In addition, like the science reviewed in chapter 2, the IPCC found that hydropower dams built on the Mekong mainstream and its tributaries will have severe impacts on fish productivity and biodiversity through the blockage of fish migration routes, altered habitat, and reduction of nutrient flows downstream.

While on the surface, the construction of the cascade seem to offer a means of adaptation to these changes – as claimed by the Water Resource Bureau and

Hydrolancang (Zhang 2012; Gao and Zhong 2014) – the IPCC, along with Grumbine et al (2012) and Rasanen et al (2012), claim that climate change impacts will exacerbate the negative changes from hydropower development on both the upper and lower Mekong river. So, while the cascade and its reservoirs may indeed offer some protection from drought and flood impacts in the future, in the more near term (10-20 years), it seems likely that the negative impacts of decreased fishing yields, less fertile floodplains, and decreased biodiversity will reduce the Southeast Asia’s resiliency and adaptive capacity to the growing impacts of climate change, which will only exacerbate the negative

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impacts of hydropower. That said, it is difficult to assess the value of a fully functioning and fully coordinated upper Mekong dam cascade, and its potential to bring relief from droughts and floods. The extent to which this the dams will bring both positive and negative impacts is highly dependent on its flow management (He et al 2006).

As briefly touched upon in previous chapters, there are generally two primary ways in which to manage a dam: for flood and drought protection or for electricity production. For an operation method focusing on preventing floods and relieving

droughts, the dam is typically conducted as such: the reservoir is emptied during the dry season until flood season begins, where the reservoir then begins to store as much as possible to lower flood levels. Typically the reservoir will run at capacity until the season ends. The dry season then gains the supplemented water flow. However, this conflicts with the second operation method, electricity production. By taking on water in the wet season, and draining the reservoir in the dry season it means an unsteady, inconsistent, and therefore inefficient production of electricity (Roberts 2001; Qin 2010b, 2010c). In addition, by taking on floodwaters it sediment is more likely to accumulate behind the dams.

The other operation method that prioritizes electricity production requires the dam to flush as much sediment as possible in order to maintain optimal reservoir capacity.

Electricity generation depends on flow and the head – the height of the water in the reservoir relative to the height of the water on the other side (Roberts 2001; Qin 2010b, 2010c). As such, both of these requirements equates to the dam allowing as much sediment-laden flood waters to pass in the wet season, while maintaining as high a reservoir as possible during the dry season to allow for optimal electricity production.

This would exacerbate downstream flooding and droughts, bringing an inevitable conflict between the incentives of dam operators (maintaining capacity and generating power) and downstream residents (preventing floods and relieving droughts). While careful operation management can ameliorate these impacts, i.e. not filling the Xiaowan reservoir during the dry season (Zhang 2012), Qin Hui, an academic at Qinghua University, claims

“that the requirements of electricity production require storing water flow during the wet season ” (Qin 2010a). This occurred in both the Three Gorges Dam and Sanmenxia dams have attempted this method “to varying degrees and have presented it as a great

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innovation” (Qin 2010a). However, the severe sedimentation behind the Sanmenxia dams made this a necessity, going against its original plan to be regulatory dams.

It therefore remains to be seen in the coming years as to how well Hydrolancang can balance the needs of drought relief and flood prevention versus the explicit goal of electricity production for the entirety of the cascade, except the Ganlanba dam. With climate change further exacerbating the floods and droughts, it may become increasingly difficult to balance the domestic priorities of electricity production with the regional needs of drought relief and flood prevention; the benefits with the costs. It remains to be seen whether the “scientific regulation” of the cascade (Gao and Zhong 2014) can match the feasibility concerns of the cascades critics.

While the impacts of the dams will be felt over the coming decade, and climate change will be felt over the coming decades and century. In the meantime, as suggested in Zuo et al (2010), the cascade will likely make the Lower Mekong basin (LMB) more reliant on precipitation from the monsoons that contribute a significant amount to water flow in the LMB. As such, I would argue that the cascade may, in fact, make the region potentially more vulnerable to climate change as it seems likely that the initial priority for the cascades management is electricity production over the next decade. As impacts become more apparent, the effects of climate change and energy demands will already be becoming stronger. By the time the motivation and consensus to take more actions happens, the more long-term, cumulative impacts will already have taken their toll on the resiliency of the Mekong ecosystem. Therefore, a management scheme that fully factors in the needs of a natural flow cycle, while unlikely in terms of both ability and political will, would likely come at a time that is already beyond much of the ecosystems ability to recover.