Received on: October 31, 2017
Accepted on: November 14, 2017
Published on: November 28, 2017
*Franchito SH1,Fernandez JPR1, Rao V. Brahmananda1
CPTEC Instituto Nacional
The impact of the increase of greenhouse gases (GHG) concentration on the lake-breeze circulation in the 21st century in the regions surrounding the Tucurui hydroelectric dam, Brazil, is investigated. The hydroelectric power station of Tucurui is the biggest hydroelectric power-station in Amazonia. For this purpose the Regional Climate Model RegCM4 is run for a 11-year (1989-2000) period, with one year of spin-down with the observed GHG concentration (present-day climate), and under the RCP 8.5 scenario for 2089-2100 (far future climate). The model domain covers all the South America with a horizontal grid spacing of 50 km. The simulations are downscaled to smaller area (grid spacing of 10 km) including the region of the hydroelectric dam. The results showed that the surface temperature increases around 6oC in far future climate compared with the present climate. The lake-breeze circulation enhances and provokes an increase of the advection of humidity in the region.
Lake-Breeze Circulation; Tucurui Hydroelectric Dam; Brazil; Greenhouse Gases Increase
Many studies have been devoted to understanding and evaluate the impact of climate change due to the increase of greenhouse gases (GHG) in the last decades. Projections of future climate show that the global warming have been aggravated by human activities and the extension of the problem have not precedent at least in the last 20 years. Climate change due to the increase of GHG concentration affects the climate, the hydric and agricultural resources and the ecosystem causing impacts on the human activities and the people comfort (IPCC AR5). Thus it is required a great politic effort for this mitigation.
Many studies indicate that the reservoirs, mainly in the tropics, are a signifcant source of GHG [1,2, 3]. These GHG emissions contribute to the global warming. Regions surrounding the reservoir of hydroelectric dam are inﬂuenced by lake-breeze circulations [4,5, 6]. The difference of the temperature between the water (lake) and the adjacent land may provoke a local atmospheric circulation: a lake-breeze during the day (directed from the lake to land) and a land breeze during the night (directed from land to the lake). These local winds have an important role in determining the climate in these regions because they inﬂuence the air ﬂow characteristics, the precipitation and the humidity transport. Due to crescent increase of GHG concentration lake-breezes play in future an important role in the transport of GHG to the neighbourhood of the reservoir where most of the population is concentrated. Although there are many efforts to investigate the climate change impacts on the water resources in the reservoirs and on the hydropower generation [7,8, 9, 10] studies of the inﬂuence of the GHG on the local climate are needed yet. In the case of Brazil, there are some studies taking into account the effect of lake-breezes, particularly in the Northeast , in the central portion of the Parana River valley, in the south of Brazil, near the Brazil-Paraguay border [5, 6] and Amazonia . However, the study of the impact of GHG on the local circulation in the region surrounding a hydroelectric reservoir is pioneer.
In this paper it is investigated the impact of the increase of GHG concentration on the lake-breeze circulation in the 21st century in the regions surrounding the Tucurui hydroelectric dam using the Regional Climate Model RegCM4 simulations under the scenario RCP 8.5. The hydroelectric power station of Tucurui, located in the State of Para, Brazil (Figure 1), is biggest hydroelectric power-station in Amazonia. Section 2 shows a short description of the model and simulations design. Section 3 presents the simulations for the present climate and the future projected changes, and conclusions are presented in Section 4.
Figure1: Location of Tucurui Dam. Model Domain and Topography: A) Coarse Resolution and B) Nest. The Horizontal
Resolution of the Course And Nest Are 50 Km and 10 Km, Respectively. X Point at West Side of Tucurui Dam
Resolution of the Course And Nest Are 50 Km and 10 Km, Respectively. X Point at West Side of Tucurui Dam
2. Model Description and Experiments Design
The experiments employed in the study were conducted by the Regional Climate Model ICTP RegCM version 4 (RegCM4) [13, 14, 15]. In the experiments the RegCM4 is run driven at lateral boundaries by the global model of HadGEM2. Its an Earth-System Model developed by Hadley Centre of UK Met Office, with 38 levels, horizontal resolution of 1.25o latitude and 1.875o longitude. The RegCM4 is run for a 11-year (1989-2000) period with one year of spin-down with the observed GHG concentration, considered as the present-day climate, and under the RCP 8.5 scenario for 2089-2100 (far future climate). The model domain covers all South America (see Figure 1a), following the CORDEX. It is centered at 220S, 590W, and contains 202EWx192NS grid points, with a horizontal grid spacing of 50 km over a rotated Mercator projection. The simulations are downscaled to smaller area (grid spacing of 10 km) including the region of the hydroelectric dam (see smaller area are in Figure 1b). The nest experiments are centered in the Tucurui dam (4.5oS, 49.5oW), with 118x128 lon x lat grid points.
3. Present Day and Future Changes
A) Present Day Climate
Figure 2a shows the annual cycle of the modeled and observed surface temperature. The modeled values correspond to the point situated at 4oS and 10 km inland in the western side of the dam (X point in Figure 1b). The observations correspond to mean annual values from 1961 to 1990 in the Tucurui meteorological station obtained from the National Institute of Meteorology of Brazil (INMET). As can be noted, there is a good agreement between the simulated values and the observations from August to December. However, the differences are larger from January to July. The maximum of the surface temperature in October is well simulated by the model. Figure 2b-d shows the annual cycle of the u and v wind components, and the precipitation. Again the observations correspond to the mean annual values (1961-1990) obtained from INMET. Although the simulated values of the zonal wind are larger than the observations, the model also shows the higher u values from June to November (Figure 2b). The values of the v-component are in a good agreement with the observations, mainly from April to November (Figure 2c). Figure 2d shows that there is a qualitatively agreement between the annual cycle of the modeled and observed precipitation. The values of the simulated precipitation matches well the observations from June to November).
Figure 2: Annual Cycle of the A) Temperature at 2m, B) Zonal Wind (M S-1); C) Meridional Wind (M S-1) and D) Rainfall (Mm Day-1). Simulated (Continue Line) and Observed (Doted Line)
B) Future Changes
Figure 3 shows the diurnal cycle of the simulated values at the X point (see Figure 1b) for the present and in the far future climate (2100). As can be noted, the surface temperature increases during the entire day in the future climate compared with the present day (Figure 3a). This causes an increase of the humidity, as shown in Figure 4.The higher increase occurs from 1500 UTC to 1800 UTC (around 6oC). This implies in an increase of the lake-breeze circulation. In the present-day climate the easterly zonal wind increases from 1.2 M S-1 at 0900 UTC to 2.7 M S-1 from 1200 UTC to 1800 UTC (Figure 3b). The northerly v-component decreases from 1.2 M S-1 at 0900 UTC to approximately 0 m-1 from 1500 UTC to 2100 UTC (Figure 3c). Thus, the horizontal wind is predominantly in the zonal direction in the afternoon. For the far future climate the u -component reaches 2.4 M S-1 from 1200 UTC to 1800 UTC and the v-component increases during the entire day compared to present climate. The increase of v-component is higher from 0600 to 1200 UTC (higher increase of 0.6 M S-1 at 0900 UTC). During the afternoon the increase is lower which favours the horizontal wind in the zonal direction. The lake-breeze in the X point ﬂows eastward in the zonal direction, perpendicular to the border of the dam (see Figure 1b). Thus the lake-breeze ﬂows in an opposite direction of the prevailing wind. Since the easterly u-component decreases in future climate in the afternoon there is an enhancement of lake-breeze circulation in the region. Due to the increase of lake-breeze circulation in future more humidity is advected to the regions in the surroundings of the dam, as shown in Figure 3 & 4.
The results indicated that the lake-breeze features in the present climate are similar to earlier studies for hydroelectric dams in Brazil, such as [8, 13] which also shows higher values of the surface temperature and lakebreeze winds between 1500 UTC and 1800 UTC. For the case of the far future climate there is a lack of studies of the effect of the increase of GHG concentration on the lake-breeze circulation near a hydroelectric reservoir. Thus, the results of the present paper must be compared with future studies of the impact of the GHG emissions on the local circulations in the surroundings of a hydroelectric dam.
Figure 3: Simulated Diurnal Cycle of: A) The Surface Temperature (0C) In Land (10 Km Westward from the Dam, X Point), B) Surface Zonal Component of the Wind (M S-1), C) Meridional Wind (M S-1) for the Present day Climate and Far Future Climate. For The Location of the X Point See Figure 1b. Solid Lines Correspond to the Present Climate and Dashed Lines to the Future Climate
Figure 4: The Same as in Figure 3, but for the Specific Humidity
In this paper the impact of the increase of GHG concentration on the lake-breeze circulation in the 21st century in the regions surrounding the Tucurui hydroelectric dam, Brazil, is investigated. For this purpose, the Regional Climate Model RegCM4 is run for a 11-year (1989-2000) period with one year of spin-down with the observed GHG concentration, considered as the present-day climate, and under the RCP 8.5 scenario for 2089-2100 (far future climate). The results showed that in the future climate surface temperature increases around 6oC compared to the present-day climate in a point located at 10 km westward from the border of the dam. This favours the increase of the lake-breeze circulation. In this point the wind during the afternoon is predominantly in the zonal direction to the west. The lake-breeze ﬂows eastward perpendicular to the border of the dam in an opposite direction of the prevailing wind. Since the easterly u-component decreases during the afternoon in future climate there is an enhancement of lake-breeze circulation and a larger increase of humidity in the region.
The results for the present climate agree with previous studies of lake-breeze in hydroelectric dams in Brazil. For the case of far future climate the investigation of the impact of GHG emissions near a hydroelectric reservoir is pioneer. So future studies are needed to compare with our results. The results may provide information suitable for discussion on the effects of GHG emissions in the scope of electric sector in Brazil.
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