This study evaluates the effect of climate change on daily rainfall, especially on the mean number of wet days and the mean rainfall intensity. Assuming that the mechanism of daily rainfall occurrences follows the first-order Markov chain model, the possible changes in the transition probabilities are estimated by considering the climate change scenarios. Also, the change of the stationary probabilities of wet and dry day occurrences and finally the change in the number of wet days are derived for the comparison of current (1x CO2) and 2x CO2conditions. As a result of this study, the increase or decrease in the mean number of wet days was found to be not enough to explain all of the change in monthly rainfall amounts, so rainfall intensity should also be modified. The application to the Seoul weather station in Korea shows that about 30% of the total change in monthly rainfall amount can be explained by the change in the number of wet days and the remaining 70% by the change in the rainfall intensity. That is, as an effect of climate change, the increase in the rainfall intensity could be more significant than the increase in the wet days and, thus, the risk of flood will be much highly increased.
핵심용어 : 레인가든, 유출저감, 저영향개발, 침투성능
AbstractThis study conducted a field experiment to estimate the characteristics of the rain garden installed at the site near Haman, also proposed a one-dimensional model to simulate the infiltration and runoff from the rain garden. This model was used to evaluate the rain garden using the rainfall data after the installation and during the last 10 years. Also, this model was applied to the annual maximum rainfall events to quantify the size of the impervious area that the rain garden can offset the adverse effect. The results are summarized below. (1) Hydraulic conductivity of the rain garden was estimated to be about 0.0188 m/hr by the variable-stage experiment. Also, the simulation experiment using the last 10 years rainfall data over the entire roof area showed that the infiltration amount is about 90.38% out of the total rainfall. (2) Infiltration simulation of the annual maximum rainfall events during last 10 years showed that the rain garden can offset the impervious area with its size about 30 times of the rain garden surface.
The probable maximum flood (PMF) is the flood caused by the probable maximum precipitation (PMP). A unit hydrograph (UH) is generally used to derive the PMF for the given PMP, but a method is needed to modify the UH parameters to reflect the PMP condition. This study presents a new method using the estimated channel velocity to modify the Clark UH parameters under the ordinary condition into those under the PMP condition. This study considers major dam basins in Korea and evaluates the application results in comparison to several previous studies. As application results of the proposed method, the Clark UH parameters under the PMP condition are found to be within the range 39–53% of those under the ordinary condition, with their mean ofabout 44%. The UH derived by applying this mean ratio shows that its peak time and the peak flow are just 44 and 227% of the UH under the ordinary condition, respectively. This change from the ordinary condition to the PMP condition is more extreme in Korea than that in Australia and the United Kingdom. This extreme change seems to be due to the climate in Korea, located in the Asian Monsoon region.
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