기후변화 대응을 위한 물환경 관리전략 및 정책방향(I)

Abstract

Water Environment Management Strategy(Ⅰ)：Response to Climate Change This study arose from research on past changes in the water and aquatic environment and analysis of the vulnerabilities therein in response to climate change. Its purpose was to evaluate potential vulnerabilities in sediment yield and water temperature fluctuation (as both are factors particularly susceptible to increases in temperature and fluctuations in rainfall, in particular during flood season), and then provide forecasts with respect thereto. To evaluate sediment vulnerability to climate change and determine prospects for future sediment yield, a water erosion prediction project model was first employed for a portion of alpine cultivated land in the Han River basin. Comparative analysis of outflow, peak outflow, and sediment discharge was performed using probable rainfall data sorted by frequency for each region. Results indicated that rainfall had increased 167% for the two year and 300 year frequency. Outflow had increased 249.4%, and peak outflow had increased 193.9%, while sediment discharge had increased 906.2%. Accordingly, this study found that outflow and soil erosion had increased substantially along with changes in the characteristics of rainfall (e.g. the intensity thereof) requiring the establishment of appropriate policies to mitigate impacts by these changes. Furthermore, sediment yield vulnerability during flood season was evaluated through assessment of peak times of concentration (Tc ) using a kinematic wave equation, while a vulnerability map was developed for the total area of the Han River basin. Future prospects for sediment yield were deduced using 50 daily precipitation ensemble scenarios attained via the statistical regional down-scaling method and Markov Chain model based on the A2 scenario from the Korea Meteorological Administration, as well as bias correction. As a result, past vulnerability in sediment management during the flooding of the Han River basin was found to have fluctuated in the watershed characteristics of the basin(e.g. landcover) In a future climate change scenario (excluding some river basins) vulnerability will increase by 7.7% from 2011 to 2050, and by 11.3% from 2051 to 2090. Accordingly, appropriate management directives will likely be needed, including use of ground residue to create water impermeable areas with Low Impact Development(LID) and other policies to address issues with respect to the soil surface. Furthermore, river basins assessed as having high vulnerability should be evaluated for their eligibility for more intensive sediment management techniques. To perform analysis and evaluation of the effects of climate change on water temperature in rivers and reservoirs, this study first reviewed statistical trends in air temperature data over the last 20 years from meteorological observatories around the country via the Mann-Kendall method. Analysis of changes in water temperature were undertaken with the seasonal Mann-Kendall method using average water temperatures for rivers and wetlands located in the meso-scale watershed for the river in question, using data from 649 monitoring points operated from 1995 among the national water quality monitoring points (1989~2008, n=144,765). Evaluations on changes in water temperature and statistical significance were then carried out. Linear and non-linear analysis was undertaken to elucidate the relationship between the foregoing air temperature data and water temperatures, allowing examination of the extent of changes in water temperatures vis-a-vis changing air temperatures. The A1B climate change scenario for the Korean peninsula provided by the Korea Meteorological Administration was used to forecast changes in water temperatures in line with climate change, and water temperatures were forecast up to the year 2100. Future changes in “DO(Dissolved Oxygen),” the most sensitive item with respect to changes in water temperature, were also forecast. Survey data and long term water temperature data for the national water quality monitoring points and aquatic environment information systems in this study were divided into two broad categories, "rivers" and "reservoirs". Among a total of 97 meso-scale watersheds, 42 showed a trend towards lower water temperatures, while 57 showed a trend towards higher water temperatures. As no clear pattern emerged from the data, additional, more precise surveys and analysis of the causes of water temperature changes will be required. Fourteen meso-scale watersheds had statistically significant temperature increases (95% confidence interval), with six in the Han River watershed, five in the Nakdong River watershed, and three in the Seomjin/Yeongsan River watershed. Ten meso-scale watersheds exhibited declining temperatures, with the Geumgang River having the largest number at five (figure 5). Furthermore, reservoirs had more clearly visible trends in their statistically significant water temperature fluctuations. Among reservoirs with increased water temperatures, the Nakdong River watershed accounted for six locations, or 46% of the total, and also had the largest number of meso-scale watersheds with increased air temperatures, followed by the Han River, the Yeongsan/Seomjin Rivers, and the Geumgang River. Basins that experienced declining temperatures included a total of eight meso-scale watersheds, including five in the Yeongsan/Seomjin River water shed, accounting for 63% of the total. Climate change is likely to exert a large direct and indirect influence on water quality and the ecology of rivers and reservoirs due to increased water temperature and changes in water volume. A decline in oxygenation, increased stratification/eutrophication, and reductions in light penetration and nutrient supplies will likely cause various water quality and ecology problems, including declining biological productivity. However, and notwithstanding the immediacy of the issues involved, detailed research findings with regard to the effects of climate change on water quality and water ecology are still very limited. This situation is largely due to a lack of systematic long-term monitoring data. Accordingly, it is imperative that a more systematic water quality monitoring system be built to collect and analyze data, and priority should be put on collecting high quality data when assembling the data. For example, present water temperature data allows the input of only integer values, causing uncertainties in analysis of long term water temperature trends and determination of statistical significance. Furthermore, comprehensive review will be needed of the effect of this analysis on policy and proposals to reflect such results therein. In particular, in comprehensive regulation of water pollution, methodologies are needed that consider climate change effects when assessing pollution load and forecasting water quality, as well as evaluations that assess climate change effects when determining achievement of pollution load reduction goals. The effects of climate change on the water and aquatic environment as visible in the data have in the past been highly dependent on the quantitative results of research on water quality and due to this uncertainty, interest in research in this area is not high. One of the causes for this is that a very diverse range of natural (i.e. climatological) and manmade factors have contributed to changes in the environment. Understanding of the causes of changes, in the environment, particularly with respect to the occurrence of pollution and the channels thereof, is subject to many of the same limitations as for understanding the effects of climate change. However, with abnormal climate events on the rise recently, and pressure from pollution continuing to accelerate, the need for protection of water quality and watersheds has grown more acute, and in the future, will be an increasingly important issue in both social growth and the protection of the natural world. Furthermore, serious climate change will negatively affect the management (i.e. use and delivery) of water resources (e.g. volume and flow, quality, and ecology). This will require the establishment of management strategies at the national level in terms of national water security(Korea Environment Institute, 2009).