Effects of Climate Change and Variation on Reservoir Systems and Remedy Models
The effects of climate change and variations cannot be overlooked for projects that are currently coming up and whose lifespan is expected to last long. Reservoirs are suchlike projects and are therefore likely to encounter climatic changes once serious effects start being experienced. The climate changes could range from increased temperature to increased rainfall that could lead to increased evaporation rates and flooding respectively. The objective of this research, through previously conducted studies, is to identify the best possible models that could be employed during designing and construction of reservoirs that will promote their adaptation to climate change.
Effects of climate change on nature
Reservoirs are particularly important because they store water for various uses. They include generation of hydroelectricity, water for domestic use, water for agricultural use and the water for industrial use. As such, the reservoirs are important. However, the levels of water in the reservoirs are always in various risks both natural and human induced. Human-related risks include the consumption of the water from the reservoirs and the rivers and streams supplying water to the reservoirs. For example, the intensive farming activities in the upstream parts of the rivers supplying water to the reservoirs may lead to the high usage of water for irrigation. Consequently, the water that flows downstream may either be less than required or may contain too much silt, in the case of poor farming practices.
Naturally induced water level variations are mainly brought about by the changes in the climatic and weather conditions. For example, rainy conditions in the upstream parts of the river on which a reservoir is located, imply that there will be high water level. Conversely, if prolonged dry weather conditions are experienced on the upstream side of the reservoir, the water levels will be low throughout the said period. Weather conditions also determine the water discharged from the reservoirs for use on the downstream parts of the river. This implies that the rate of water replacement will be less than the rate of water discharge during the dry season while the inverse is true during the wet season. The human-induced risks affect the water demand while the weather and climatic variations influence the supply of the water to the reservoirs.
The changes in water levels in the dams have various effects on the usage of the reservoirs and its water. High water levels cause the erosion of the shoreline. This consequently results in the increased cost of replacement of the eroded landmass and maintenance of the eroded areas and affected infrastructural entities. Low water levels in the reservoirs affect navigation, the generation of hydroelectricity, the ecosystem of the area, the recreation activities that were being carried out before the subsiding of the water levels and also health problems. As a result, it is important for designers and constructors of dams and reservoirs to come up with models that will help them in adapting their designs to the changing climatic conditions. This should be done in a bid to reduce the effects that the variations and changes would have to the reservoir would have to the ecosystem and to the reservoir itself (Ec.gc.ca).
Climate and climate change
The climate is referred to as the average weather conditions of a place taken over a prolonged period mainly between 25 to 30 years. Climatic change and climatic variations, therefore, refer to the alteration of the climatic conditions normally experienced in that particular place. The climate is an amalgamation of such weather variables as temperature, precipitation, and specific humidity. The change in the climate is observed from the changes in rainfall and temperature. The two weather entities determine the specific humidity of a place as the latter is not a significant weather measurement object.
The changes in rainfall are measured regarding an increase or a decrease in rainfall. An increase in the rainfall will cause an increase in the relative humidity of the atmosphere. As a result, there will be minimal evaporation of the water in the reservoirs, and this will ultimately cause an increase in the water levels and a consequent increase in the discharge of water. A decrease in rainfall will have a reverse effect in that the relative humidity will be low, and therefore evaporation to the atmosphere will increase. This will cause a reduction in the water levels in the reservoir and ultimately cause decreased discharge. On the other hand, temperature changes are gauged depending on their increase or decrease.
Increased temperature will cause increased glacial melting, and this will have a corresponding short term and long term effects. The short-term effects are that they will increase the volume of water in the reservoirs thus increasing the water discharge. However, in the long run, when the entire glacier has melted, there will be little water left to flow into the reservoirs, and therefore, the discharge will have decreased. When the temperature drops, there will be a corresponding reduction in evaporation, and this will cause an increased release from the reservoirs.
The climate change is majorly caused by the increased carbon dioxide emissions to the atmosphere as a result of industrialization and the destruction of forests. The General Circulation Models (GSM) provided by the Intergovernmental Panel on Climate Change (IPCC) project that the average temperature of the earth will increase by approximately 3° by 2080. It is also projected that the annual river flow will have increased by between 10 and 40 percent in the high latitude regions and decrease by about 30 percent in the tropical region compared to the present. It is also projected that due to the above, the mean sea level will increase causing frequent floods in the coastal regions. The sea water temperatures will also increase and his will consequently cause an increase in catastrophic events such as floods and droughts.
There are studies that have been conducted seeking to address the issue of climate change on reservoirs. It is important to note that the current reservoirs were not constructed with management systems for adaptations to climate change. This is mainly because there was no reliable prediction of the future climate. Therefore, the studies form the basis for future infrastructural projects whose designs will put into consideration the expected climate changes.
The case studies employed the use of the Integrated Reservoir Management System. The system involves the use of a weather generator (WG) model, a hydrological model (HM) and an optimization model. The WG examines the future climatic variables; the HM changes a future scenario to hydrological variables while the optimization model develops an adaptation to climate change in the reservoir. The system is particularly important because it can provide information showing the adaptations to climate change for a specific scenario and once the scenario changes, the system can also provide the adaptations. The WG model in full stands for the K-nearest neighbor weather generator model and provides credible weather conditions influenced by the changes in climate based on the output from the GCM (Eum, Arunachalam, and Simonovic 2).
The HM in full stands for the streamflow synthesis and reservoir regulation (SSARR) hydrological model while the optimization model is a short form for differential evolution optimization model. The latter uses streamflow scenarios for future weather generated from the former to develop the best reservoir operational policies that are consistent with the predicted scenario. The results are represented in a rule curve whereby the curves for the predicted scenarios are compared to the curves of the current scenarios. The system integrates the three modules.
The WG module essentially uses an improved version of the K-NN algorithm known as the WG-PCA. The latter introduced a key analysis component to the perturbation process, computation procedure and preservation of input data of the former. The purpose of the analysis was to reduce the size of the mean vector of the current days and that of all the nearest neighbor values. The HM was developed to provide hydrological simulations for functioning river prediction and river basin management activities. The HM can be used to predict the stream flows in the river as well as the surface runoffs on the river basin. It can also be used to perform prolonged climate change impact studies. To generate the streamflows, the HM (full acronym SSARR) requires an input data of the precipitation and the temperature. The model used for the studies incorporates calibration from previously conducted studies that used the model.
Finally, the differential evolution (DE) optimization model uses the DE algorithm optimizes problems over a continuous domain. The DE algorithm is advantageous because it is easy to use, has an uncomplicated structure, fast convergence, and strength in its application. It narrows down its search using the mutation and selection processes. The HM uses data generated from the WG to generate information that is then fed into the differential evolution optimization model (DEOM). The final product of the process represents a reservoirs adaptation to climate change.
Case study I
The study was conducted in the Nakdong River Basin in South Korea. The river basin covers a total length of 521.5 kilometers and occupies approximately 24 percent of the country. It is, however, the second largest drainage area in the country covering a total area of approximately 23,820 square kilometers. The basin has seven multi –purpose reservoirs. They, therefore, provide 466.7 GWh and 3,032x106 cubic meters of water every year. They include Andong, Imha, Hapcheon, Nam-gang, Milyang, Young-Cheon and Unmum in the decreasing order of their relative sizes. The sizes of the reservoirs greatly determine their role in the water resource management. As such, the latter three reservoirs play a minor role.
The Nakdong River Basin had been vulnerable to drought and floods and as stated earlier; the two extremes could become more severe. With the drought that the basin experiences, the cities depending on it have experienced several water restrictions due to the reduction of the water levels in the basin. Due to the capacity, the four largest reservoirs store more than 90 percent of the water in the basin thereby also providing 90 percent of the electricity and water supply. However, when compared with the larger three, Namgang reservoir poses challenges to the management and operations team. Therefore, the study mainly focused on the three largest reservoirs namely Andong, Imha and Hapcheon.
The results from the General Circulation Models were categorized into four namely A1, A2, B1, and B2. The GCM employed scenarios obtained from the Special Report on Emission Scenarios (SERS). The scenarios factored in the entities of the country’s economy which essentially drive it. This included information on the population and the greenhouse gas emissions.