영문초록:This study was conducted in order to propose the newly developed method of evaluating hydrological droughts in semi-distributed forms using an equation based on and supplementing the existing SWSI. The SWSI evaluates the hydrological droughts in drainage areas by selectively applying one or all of the components of snowfalls, rainfalls, stream-flows, and water reservoir storage for ...
영문초록:This study was conducted in order to propose the newly developed method of evaluating hydrological droughts in semi-distributed forms using an equation based on and supplementing the existing SWSI. The SWSI evaluates the hydrological droughts in drainage areas by selectively applying one or all of the components of snowfalls, rainfalls, stream-flows, and water reservoir storage for evaluation by area and season. The Korean Peninsula has various water supply sources and types in different regions. Water supply in some regions is determined by the storagein water reservoirs; that of some others is determined by the stream-flows; and some others utilize groundwater when struck by droughts. In order to evaluate hydrological droughts, water sources both in the surface and underground should be considered. Therefore, the components involved in calculating the MSWSI included precipitation, dam inflows, stream-flows, and groundwater levels, all of which were selectively employed when making evaluations of each drainage area.Groundwater levels, which have traditionally not been considered in pre-established sources and methods, proved its utility in terms of evaluating hydrological droughts of many regions. The general Korean policies regarding droughts usually have water supplied from rivers and groundwater through pipelines where there is not enough river water or supplying water from rivers is not possible. Hence, it is essential to include the components of stream flows and groundwater when evaluating droughts. Both these components have effects to ameliorate the drought conditions. In particular, the component of groundwater levels helps greatly overcome the droughts as a substitute for stream flows. The shorter the distance between the river and the station that observed groundwater levels, the smaller the difference between where the groundwater component was added and where it was not added. Hence, there was no significant error associated with addition of this component when evaluating hydrological droughts.In order to divide the nation into regions with the same sources and types of water supply and assess the applicability of the newly developed method in drainage areas for semi-distributed drought evaluations, the nation was divided into 32 and 112 drainage areas. The evaluations were conducted in the one-month unit and the one-week unit. As a result of comparing the results of this application to the historical drought conditions, the weekly application in the 112 drainage areas matched with the actual drought history of those regions. Thus, weekly evaluations of hydrological droughts during the severe phase of droughts are necessary.The applicability of the new method was also assessed by applying it to the agricultural drainage areas. In Korea with big differences in drought conditions by area, agricultural droughts are especially sensitive to the stored amounts of agricultural water reservoirs in agricultural districts. Many systems and studies for national or regional droughts conducted so far have used traditional drought indices, such as the PDSI, SPI, and SWSI. The agricultural fields form around 22% of the total land area of South Korea, and 64% of the agricultural fields are rice paddies, which is irrigated by agricultural water reservoirs. Therefore, the applicability of the new method was assessed using the storage and inflows of agricultural water reservoirs and precipitation in agricultural districts. The MSWSI proved to be applicable to the agricultural watershed as well.Qualitative verification of the results of various types of drought evaluations is extremely difficult. Evaluation methods vary from evaluation purpose to purpose, and the analytical methods to verify the results of those drought evaluations also vary widely. This study has developed the MSWSI for hydrological drought evaluation based on supplementing the SWSI with the component of groundwater levels, and sought to evaluate droughts in more accuracy in terms of time and space through the selection process of the observed hydrological data acquired from across the nation.As a result, the study obtained hydrological data of good and accountable quality and applied them to evaluating hydrological droughts with the component of groundwater levels added to the application of the SWSI. Security of more time-series groundwater level data throughout the nation is likely to support more accurate evaluations in terms of space. The significance of this study lies in preparing for a more accountable drought evaluation system and propose its potential by verifying the results of weekly drought evaluations using various time-series hydrological data
영문초록:This study was conducted in order to propose the newly developed method of evaluating hydrological droughts in semi-distributed forms using an equation based on and supplementing the existing SWSI. The SWSI evaluates the hydrological droughts in drainage areas by selectively applying one or all of the components of snowfalls, rainfalls, stream-flows, and water reservoir storage for evaluation by area and season. The Korean Peninsula has various water supply sources and types in different regions. Water supply in some regions is determined by the storage in water reservoirs; that of some others is determined by the stream-flows; and some others utilize groundwater when struck by droughts. In order to evaluate hydrological droughts, water sources both in the surface and underground should be considered. Therefore, the components involved in calculating the MSWSI included precipitation, dam inflows, stream-flows, and groundwater levels, all of which were selectively employed when making evaluations of each drainage area.Groundwater levels, which have traditionally not been considered in pre-established sources and methods, proved its utility in terms of evaluating hydrological droughts of many regions. The general Korean policies regarding droughts usually have water supplied from rivers and groundwater through pipelines where there is not enough river water or supplying water from rivers is not possible. Hence, it is essential to include the components of stream flows and groundwater when evaluating droughts. Both these components have effects to ameliorate the drought conditions. In particular, the component of groundwater levels helps greatly overcome the droughts as a substitute for stream flows. The shorter the distance between the river and the station that observed groundwater levels, the smaller the difference between where the groundwater component was added and where it was not added. Hence, there was no significant error associated with addition of this component when evaluating hydrological droughts.In order to divide the nation into regions with the same sources and types of water supply and assess the applicability of the newly developed method in drainage areas for semi-distributed drought evaluations, the nation was divided into 32 and 112 drainage areas. The evaluations were conducted in the one-month unit and the one-week unit. As a result of comparing the results of this application to the historical drought conditions, the weekly application in the 112 drainage areas matched with the actual drought history of those regions. Thus, weekly evaluations of hydrological droughts during the severe phase of droughts are necessary.The applicability of the new method was also assessed by applying it to the agricultural drainage areas. In Korea with big differences in drought conditions by area, agricultural droughts are especially sensitive to the stored amounts of agricultural water reservoirs in agricultural districts. Many systems and studies for national or regional droughts conducted so far have used traditional drought indices, such as the PDSI, SPI, and SWSI. The agricultural fields form around 22% of the total land area of South Korea, and 64% of the agricultural fields are rice paddies, which is irrigated by agricultural water reservoirs. Therefore, the applicability of the new method was assessed using the storage and inflows of agricultural water reservoirs and precipitation in agricultural districts. The MSWSI proved to be applicable to the agricultural watershed as well.Qualitative verification of the results of various types of drought evaluations is extremely difficult. Evaluation methods vary from evaluation purpose to purpose, and the analytical methods to verify the results of those drought evaluations also vary widely. This study has developed the MSWSI for hydrological drought evaluation based on supplementing the SWSI with the component of groundwater levels, and sought to evaluate droughts in more accuracy in terms of time and space through the selection process of the observed hydrological data acquired from across the nation.As a result, the study obtained hydrological data of good and accountable quality and applied them to evaluating hydrological droughts with the component of groundwater levels added to the application of the SWSI. Security of more time-series groundwater level data throughout the nation is likely to support more accurate evaluations in terms of space. The significance of this study lies in preparing for a more accountable drought evaluation system and propose its potential by verifying the results of weekly drought evaluations using various time-series hydrological data
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