Mitig Adapt Strat Glob Change (2008) 13:193–206 DOI 10.1007/s11027-007-9086-5 ORIGINAL PAPER Methane Emissions from Large Dams as Renewable Energy Resources: A Developing Nation Perspective Ivan B. T. Lima Æ Fernando M. Ramos Æ Luis A. W. Bambace Æ Reinaldo R. Rosa Received: 14 November 2006 / Accepted: 5 February 2007 / Published online: 2 March 2007 Ó Springer Science+Business Media B.V. 2007 Abstract By means of a theoretical model, bootstrap resampling and data provided by the International Commission On Large Dams (ICOLD (2003) World register of dams. http://www.icold-cigb.org) we found that global large dams might annually release about 104 ± 7.2 Tg CH4 to the atmosphere through reservoir surfaces, tur- bines and spillways. Engineering technologies can be implemented to avoid these emissions, and to recover the non-emitted CH4 for power generation. The imme- diate benefit of recovering non-emitted CH4 from large dams for renewable energy production is the mitigation of anthropogenic impacts like the construction of new large dams, the actual CH4 emissions from large dams, and the use of unsustainable fossil fuels and natural gas reserves. Under the Clean Development Mechanism of the Kyoto Protocol, such technologies can be recognized as promising alternatives for human adaptations to climate change concerning sustainable power generation, particularly in developing nations owning a considerable number of large dams. In view of novel technologies to extract CH4 from large dams, we estimate that roughly 23 ± 2.6, 2.6 ± 0.2 and 32 ± 5.1 Tg CH4 could be used as an environmentally sound option for power generation in Brazil, China and India, respectively. For the whole world this number may increase to around 100 ± 6.9 Tg CH4. Keywords Emission mitigation Æ MDL Æ Methane recovery Æ Renewable energy Æ Reservoir Æ Spillway Æ Turbine 1 Introduction Large dams (LD) present a central role in the civilization development. In several nations, they are responsible for drinking water supply, river flood/drought control, irrigation for food production, and, more recently, for hydroelectric power genera- tion. Although LD have been essential for the well-being of mankind, there are a I. B. T. Lima (&) Æ F. M. Ramos Æ L. A. W. Bambace Æ R. R. Rosa National Institute for Space Research (INPE), Astronautas Av., 1758, S. J. Campos, SP, Brazil e-mail: [email protected] 123 194 Mitig Adapt Strat Glob Change (2008) 13:193–206 number of environmental shortcomings emerging from damming and flooding pristine river basins. The well-known worldwide impacts of LD are local people displacement (Bartolome et al. 2000), fish community alteration and vanish of commercial fishery practices, lost of biodiversity, lost of natural and agricultural terrestrial ecosystems (Berkamp et al. 2000), and the emission of greenhouse gases to the atmosphere (Rosa and Santos 2000), especially methane (CH4). In fact, the practice of flooding terrestrial ecosystems might be altering atmospheric CH4 since the past five thousand years (Ruddiman 2003; Ruddiman et al. 2005). After carbon dioxide, CH4 is the most important greenhouse gas. It is responsible for more than 20% of change in the radiative forcing due to anthropogenic green- house gas emissions to the atmosphere (Shindell et al. 2005). The anthropogenic increase of the CH4 mixing ratio in the atmosphere after the XVIII century has been attributed to coal, natural gas, forest clearing/burning, landfill, domestic ruminants and rice cultivation (Wuebbles and Hayhoe 2002). Several authors have shown that LD may also represent a fraction of the anthropogenic CH4 (Saint Louis et al. 2000; Abril et al. 2005; Soumis et al. 2005; Duchemin et al. 2006). A first estimate indi- 6 2 12 cated that for a global LD area of 1.5 · 10 km about 69.3 Tg CH4 (1 Tg = 10 g) can be annually released by bubbling and diffusive processes (Saint Louis et al. 2000). Despite the uncertainties on LD upstream (reservoir surface) emissions, a forming consensus is that LD downstream (turbines and spillways) emissions might be responsible for a substantial release of CH4 to the atmosphere (Fearnside 2002; Abril et al. 2005; Gue´rin et al. 2006; Kemenes et al. 2006). A ‘‘degas drop-pressure effect’’ arises when CH4-saturated water passes through turbines and spillways (Fearnside 2002; 2004; 2005a, b). In conjunction with turbulence, this effect may lead to cavitation phenomena, creating suitable conditions for bubble (short-term) CH4 releases immediately downstream to LD. In addition, enriched-CH4 waters may steadily (long-term) release CH4 to the atmosphere on the course of several kilometers downstream to LD (Gue´rin et al. 2006; Kemenes et al. 2006). Following this rational, Bambace et al. (2007) have proposed a series of engi- neering solutions to mitigate upstream and downstream CH4 emissions. These technologies, associated to efficient CH4 degassing and storage systems, can promote the recover of the non-emitted CH4 for power generation. In brief, turbine and spillway emissions should be controlled by gate-buoys, allowing only CH4-depleted surface waters being turbined or spilled downstream. The non-emitted CH4 can therefore be extracted upstream at the hypolimnion via CH4 degassing/storage systems (Bambace et al. 2007), before the occurrence of either surface atmospheric emission or oxidation by methanotrophic bacteria in the water column (Gue´rin and Abril 2004; Lima 2005). For Amazon LD, a first assessment indicates that power generation from biogenic CH4 is technically and economically viable (Ramos et al. 2007). In the present paper, we show updated calculations for global LD CH4 emissions. By means of a theoretical model, bootstrap resampling and data provided by the International Commission On Large Dams (ICOLD 2003) we compute approxi- mations of upstream and downstream LD CH4 emissions. We further estimate the potential power generation from LD CH4 recovery in the world, and in three important developing nations owning a considerable number of LD, namely Brazil, China and India. 123 Mitig Adapt Strat Glob Change (2008) 13:193–206 195 2 Data sources, model premises and parameterization Although most premises in the present model are based on published information, chosen parameters can be very specific, and a case-by-case model would be rather impracticable for 31,148 LD available in ICOLD (2003) between 1880 and 2005. The model is then an a priori assessment, and an effort to extend the global empirical information is necessary to better define model parameters and to improve the results herein obtained. 2.1 Annual upstream CH4 emission model Annual upstream CH4 emission estimations (fup) were made by using empirical equations determined for temperate lakes by Bastviken et al. (2004, Table 2, p. 6), relating lake surface area to diffusive, bubble and storage (overturn) CH4 emissions. There are in total 33,071 registered LD in ICOLD (2003). From 1880 to 2005 there are 31,148 registered LD in the world, of which 73% present surface area infor- mation (ICOLD 2003). Uncertainties in the upstream CH4 emission model are in part associated to log-log regression equations given in Bastviken et al. (2004). Log–log regression indeterminacies are approximately 22, 14 and 59% for bubble, diffusive and overturn emissions (Bastviken et al. 2004). Besides, the equations are given solely for lakes in the temperate region. After several years of impoundment, a steady state reservoir tends to present similar bacterial abundance and biomass of surrounding natural lakes (Soumis et al. 2005). It was then assumed that both temperate reservoirs and lakes might exhibit comparable steady state annual upstream CH4 emissions. We do not consider transient large emission after LD reservoir filling because the time spam to reach steady state of about 10 years is small (Abril et al. 2005; Soumis et al. 2005) in relation to the 125-year period of analysis. Furthermore, CH4 lifetime in the atmosphere was around 6.2 and 8.4 years between 1880 and 2005 (Lelieveld et al. 1998). Upstream CH4 emissions of tropical LD should be 5- to 15-fold superior to up- stream CH4 emissions of temperate LD (Saint Louis et al. 2000; Soumis et al. 2005). For this reason, it was assumed that CH4 upstream emissions in tropical LD can be roughly 10-fold superior to those in temperate LD. Another simplification and source of uncertainty in the upstream CH4 emission model is that tropical (tem- perate) LD were considered those that at lest 50% of the LD nation area is within (outside) the equatorial region between 20° N and 20° S. The same was done for the downstream CH4 emission calculations. For consistency assessment in the upstream emission model, we calculated local mean (±1 standard deviation, SD) and median CH4 emission factors for temperate and tropical LD, and compared them to empirical values of a recent compilation (Table 1). Such compilation however does not include overturn emissions (Soumis et al. 2005). Although all uncertainties cannot be fully assessed for model optimi- zation, the output of the upstream CH4 emission model is reasonably consistent to empirical data. The model and empirical means were of similar magnitude in both temperate and tropical cases (Table 1). For the tropical case, the model median is about 2.3 above the empirical median, while the separation between model and empirical means is quite narrow. In general, empirical means are 4.8 and 1.2 greater than model means. Coefficients of variation are between 38 and 43% in model and 123 196 Mitig Adapt Strat Glob Change (2008) 13:193–206 Table 1 Local upstream mean (±SD) and median CH4 emission factors for large dams in the world by 2005 Local mean ± SD, Local median, n Ref. –2 –1 –2 –1 mg CH4 m d mg CH4 m d Temperate 11.5 ± 4.40 10.8 17315 This studya 55.1 ± 84.7 9.30 26 Soumis et al.