Independent Rainfall Events Research Articles

A Bayesian deep learning approach for video-based estimation and uncertainty quantification of urban rainfall intensity

Accurate, high-resolution spatiotemporal estimates of rainfall intensity (RI) are essential for effective prevention and control of urban flooding. Traditional methods are often costly and provide inadequate coverage. Meanwhile, the associated uncertainty of RI estimates is often overlooked, potentially leading to poor decisions in management of urban floods. Here we examine the potential of video imagery recorded by surveillance cameras in urban areas, for providing real-time estimates of RI. Specifically, we propose the use of Bayesian deep learning (DL) to estimate RI and its related uncertainty in a real-time manner. Our DL approach combines the strengths of convolutional neural network (CNN) and long short-term memory (LSTM) to construct a suitable model for this task, and uses variational inference to quantify the uncertainty of the CNN-LSTM model. The proposed approach is tested using video imagery captured under various light-intensity conditions, including daytime, nighttime, early morning, and early evening, and evaluated via experiments using both random samples and independent rainfall events. Further, we show that the temporal processing provided by the LSTM network is important to achieve good performance of RI estimation. The results indicate the strong potential for leveraging urban camera networks to obtain high-precision spatiotemporal RI estimates at low cost, which can be extremely valuable for implementing effective flood control measures and planning emergency responses in the urban areas.

Estimating the natural disaster ınter-event time defition (NIETD) to define compound natural disasters in South Korea

Previous study on natural disaster events has been conducted under the assumption that each event is independent of others, which underestimates the risk of natural disasters by ignoring interactions between events. To solve this problem, the concept of compound natural disaster (CND) which is the combination of events has been proposed; however, there is no quantitative method for defining CND. The aims of this study are to examine the estimation methods for IETD (Inter-Event Time Definition), which separates continuous rainfalls into independent rainfall events, and to define NIETD (Natural disaster Inter-Event Time Definition), which is a criterion for determining the independence of natural disasters. This study used the method of average annual number of events for estimating NIETD. Two natural disasters can be defined as CND if the duration between them is less than the NIETD. We estimated the NIETD as 8 days using natural disasters that occurred in South Korea and identified a total of 89 CNDs of 14 different types such as consecutive rainfall events. The largest number of CNDs was caused by the combination of rainfall and typhoon, which also resulted in the most damage. To examine the randomness of event occurrences, we applied a bootstrapping approach and found that there is no evidence of randomness. The frequency analysis showed that CNDs consisting of rainfall and typhoon (7.6years), and consecutive rainfalls (9.4years) had overwhelmingly more frequent occurrences than other types. The CND definition and concept proposed in this study could be useful in the research on CND.

Effect of minimum inter-event time for rainfall event separation on rainfall properties and rainfall erosivity in a humid area of southern China

An appropriate rainfall event definition helps to have more explanatory power in research on the effect of rainfall on runoff and soil erosion. The constant minimum inter-event time (MIT) criterion is a widely accepted method used to delineate independent rainfall events from continuous rainfall records. To explore the effects of the MIT selection on rainfall event properties, rainfall erosivity and its relationship with eroded sediment, 5-min interval rainfall data from 2016 to 2021 and runoff data from 2019 to 2021 were observed continuously for a bare plot site in a humid area of southern China. The results showed that increase in the MIT criteria had an important impact on the properties of erosive rainfall events, such as reducing rainfall frequency, increasing duration, and reducing the average rainfall intensity. Furthermore, the MIT increased continuously, changed the statistical relationship between rainfall and sediment erosion, and logarithmically increased the rainfall threshold for a certain cumulative eroded sediment probability. With continuous increase in the MIT, the total kinetic energy, maximum 30 min intensity, and rainfall erosivity of rainfall events increased as a power function (r2 greater than 0.97). On the rainfall event scale, the linear relationship between EI30 and eroded sediment is the closest when MIT = 4 h. Thus, more attention should be given to the use of the MIT criterion for rainfall event identification, as it relates to the properties of rainfall events and rainfall erosivity.

Source identification of water-insoluble single particulate matters in rain sequences

In this study, eight independent rainfall events were sampled sequentially from September 20, 2019 to June 15, 2020, in Bartın province located on the western Black Sea coast of Turkey. Manually collected volume-based sequential samples were analyzed for pH and water-soluble ions involving F−, Cl−, NO3−, SO42−, PO43−, Na+, K+, NH4+, Mg2+, and Ca2+. Total trace and major elements (sum of soluble and insoluble fractions), and elemental and organic carbons (EC and OC) contents of the sequential samples were measured. Water-insoluble particulate matter in the sequential samples were characterized for their sizes, morphologies, and compositions by using Scanning Electron Microscopy Energy Dispersive X-Ray Spectrometry (SEM-EDS) and a particle size analyzer. Results of SEM-EDS, particle size distributions, chemical analyses, and the upper atmospheric back trajectories were used to apportion the sources of the water-insoluble single particulate matters in sequential rain samples. Using the proposed method, iron-steel facilities, and thermal power plants were identified as the significant regional sources. Urban traffic and natural emission were identified as the local sources.

Spatiotemporal variability of event‐based rainstorm: The perspective of rainfall pattern and concentration

AbstractRainfall pattern (RP) and precipitation concentration (PC) are two critical indices for measuring rainfall. Detecting their changes under global warming helps to understand better the rainfall variability and the flooding formation. Using the Guangdong Province, China, as a study case, five criteria were used to determine the independent precipitation events for hourly precipitation data from 1967 to 2012. The RP and PC of the events were identified, and then, their spatiotemporal variability was investigated further. The results show that (a) the occurrence frequency during 46 years, average rainfall amount and duration of independent rainfall in the coastal areas were higher than in other regions. (b) The dominant RPs in Guangdong are unimodal (more than 70%), especially the pattern with early peak (mode I; 39.5%); however, the number of stations with mode I as dominant RP decreased over time, while those with mode III (the pattern with late peak) increased. (c) Precipitation concentration index can be used for measuring the concentration of independent rainfall events, and its fixed minimum inter‐event time has significant impacts on RP and PC. The PC of the events with early peak is higher, and the concentration in the west is generally higher than those in the east under different RPs.

Spatial regression approach to estimate synthetic unit hydrograph by geomorphic characteristics of watersheds in arid regions

Rainfall-runoff relationship in arid regions is unique and challenging to study. Studies for bridging the hydro-meteorological knowledge gap for planning, designing and managing water resources is therefore vitally important. The objective of this study is to develop a method for estimating unit hydrograph at reasonably finer time resolutions (10-min and 1-h) which can be easily adaptable by practitioners at sub-catchment levels, especially when the focus area is ungauged. Observed wadi-flow at 5-min interval and tipping bucket rainfall measurements at 1-min interval were obtained to cover 10 major watersheds in Oman. The deconvolution method was applied to derive the unit hydrographs (UHs) from wadi-flow and excess rainfall. Key catchment characteristics such as the watershed area, length of the main wadi and the length to the centroid of the catchment area were derived from digital elevation model (DEM) data. The whole study area was then divided into 515 sub-catchments with various shapes and sizes. A strong relationship was found between the wadi length and the length to the centroid of the catchment area (R2>0.89). This relationship was then adopted to simplify the classical Snyder method to determine UHs. Moreover, several parameters of the Snyder method were calibrated to the arid environment by matching the peak-flow, lag-time and three time-widths (75%, 50% and 30% of the peak-flow) of 10-min and 1-h UHs with physical characteristics of the watersheds. All developed relationships were validated with independent rainfall and wadi-flow events. Results indicate that the calibrated parameters in these arid watersheds are quite distinct from those suggested for other regions of the world. A marked difference was found between the 10-min UHs estimated by the S-hydrograph method and the deconvolution method. Therefore, it is concluded that a method depends on natural hydro-meteorological conditions would be more practical in arid region. The proposed methodology can be used for water resources management in arid regions having similar climate and geographical settings.

The performance of the IMERG satellite-based product in identifying sub-daily rainfall events and their properties

Sub-daily rainfall information is essential for many hydrological applications, but ground-based data availability is still an issue in poorly gauged regions worldwide. Satellite remote sensing missions, such as the Global Precipitation Measurement (GPM) mission, have been playing a key role in estimating sub-daily rainfall data globally. However, the quality of such information needs to be carefully evaluated. Previous studies evaluating sub-daily data from the Integrated multi-satellitE Retrievals for GPM (IMERG) product considered only the rainfall depth over pre-defined periods (e.g., hourly or half-hourly), with no analysis of the ability and quality of the product in defining the actual rainfall events and the associated properties. Thus, the objective of this study is to evaluate the performance of the IMERG Final Run Version 06B (V06B) product in capturing sub-daily rainfall events and their properties (depth, duration and intensity) over Brazil. The analysis consisted of comparing the satellite estimates against the ground-based data from 1757 sub-daily rainfall gauges for a period of three years (2015–2017). This study used the minimum inter-event time (MIT) criterion to define independent rainfall events determined by dry periods: 1, 6 and 24 h. Results show that IMERG can properly estimate the sub-daily rainfall depth for the three MITs considered, with the best results found in the southern part of the country. This means that the IMERG product represents a good source of sub-daily rainfall depth data for hydrological and hydroclimatic applications in Brazil. On the other hand, the evaluation shows large overestimations and underestimations of the IMERG product for rainfall duration and intensity properties, respectively. The results obtained from this study provide a reference for IMERG users who require sub-daily rainfall data based on events and further knowledge about its properties.

Dependence Between Extreme Rainfall Events and the Seasonality and Bivariate Properties of Floods. A Continuous Distributed Physically-Based Approach

This paper focuses on proposing the minimum number of storms necessary to derive the extreme flood hydrographs accurately through event-based modelling. To do so, we analyzed the results obtained by coupling a continuous stochastic weather generator (the Advanced WEather GENerator) with a continuous distributed physically-based hydrological model (the TIN-based real-time integrated basin simulator), and by simulating 5000 years of hourly flow at the basin outlet. We modelled the outflows in a basin named Peacheater Creek located in Oklahoma, USA. Afterwards, we separated the independent rainfall events within the 5000 years of hourly weather forcing, and obtained the flood event associated to each storm from the continuous hourly flow. We ranked all the rainfall events within each year according to three criteria: Total depth, maximum intensity, and total duration. Finally, we compared the flood events obtained from the continuous simulation to those considering the N highest storm events per year according to the three criteria and by focusing on four different aspects: Magnitude and recurrence of the maximum annual peak-flow and volume, seasonality of floods, dependence among maximum peak-flows and volumes, and bivariate return periods. The main results are: (a) Considering the five largest total depth storms per year generates the maximum annual peak-flow and volume, with a probability of 94% and 99%, respectively and, for return periods higher than 50 years, the probability increases to 99% in both cases; (b) considering the five largest total depth storms per year the seasonality of flood is reproduced with an error of less than 4% and (c) bivariate properties between the peak-flow and volume are preserved, with an error on the estimation of the copula fitted of less than 2%.

The Role of the Spatial Distribution of Radar Rainfall on Hydrological Modeling for an Urbanized River Basin in Japan

Recently, the use of gridded rainfall data with high spatial resolutions in hydrological applications has greatly increased. Various types of radar rainfall data with varying spatial resolutions are available in different countries worldwide. As a result of the variety in spatial resolutions of available radar rainfall data, the hydrological community faces the challenge of selecting radar rainfall data with an appropriate spatial resolution for hydrological applications. In this study, we consider the impact of the spatial resolution of radar rainfall on simulated river runoff to better understand the impact of radar resolution on hydrological applications. Very high-resolution polarimetric radar rainfall (XRAIN) data are used as input for the Hydrologic Engineering Center–Hydrologic Modeling System (HEC-HMS) to simulate runoff from the Tsurumi River Basin, Japan. A total of 20 independent rainfall events from 2012–2015 were selected and categorized into isolated/convective and widespread/stratiform events based on their distribution patterns. First, the hydrological model was established with basin and model parameters that were optimized for each individual rainfall event; then, the XRAIN data were rescaled at various spatial resolutions to be used as input for the model. Finally, we conducted a statistical analysis of the simulated results to determine the optimum spatial resolution for radar rainfall data used in hydrological modeling. Our results suggest that the hydrological response was more sensitive to isolated or convective rainfall data than it was to widespread rain events, which are best simulated at ≤1 km and ≤5 km, respectively; these results are applicable in all sub-basins of the Tsurumi River Basin, except at the river outlet.

A statistical approach to radar rainfall estimates using polarimetric variables

To improve the accuracy of radar rainfall estimates, this study examines rainfall relationships derived from polarimetric variables calculated from Drop Size Distributions (DSDs) measured by POSS (Precipitation Occurrence Sensor System) and PARSIVEL (PARticle Size and VELocity) disdrometers for eight different rainfall events in Korea associated with the Changma front, low pressure systems, typhoons, or the indirect effects of typhoons.Analysis of the correlation coefficients between polarimetric variables as independent parameters shows that multicollinearity is expected for Z–KDP, Z–AH, and KDP–AH. Of these, R(Z, KDP) is the only relationship that had too low an accuracy for application to radar rainfall estimation. R(Z, ZDR, KDP) and R(Z, KDP, AH) were also omitted from this analysis because their intercept coefficients were too large.Analysis of the sensitivity of radar rainfall estimation to DSDs variation shows that the latest observed DSDs perform well, as much as 2.4 mm h−1 for RMSE (Root Mean Square Error) and 0.23 for NE (Normalized Error) in maximum. The statistical scores of each radar rainfall estimator vary between different rainfall events. This paper examines a new approach to radar rainfall estimation that is similar to the ensemble technique widely used in numerical prediction models. The ensemble members were chosen based on the average and standard deviation of their RMSE and NE for eight rainfall events. Two different weighting schemes were applied to each ensemble and the members were weighted equally or, alternatively, weighted based on their statistical scores. The performance of eight ensemble sets was examined using four independent rainfall events. There is little difference in the accuracy of each ensemble with respect to the weighting scheme applied. An ensemble composed of R(Z,ZDR), R(Z), and R(KDP), all given an equal weighting, was the most accurate.

Comparison of annual maximum rainfall events of modern rain gauge data (1961–2010) and Chukwooki data (1777–1910) in Seoul, Korea

Abstract In this study, the annual maximum rainfall event series were constructed and compared for both the modern flip-bucket type rainfall data, collected since 1961 (the modern data), and the old Chukwooki rainfall data, collected from 1777 to 1910 (the Chukwooki data). First, independent rainfall events were derived, by applying the same rainfall threshold of 2 mm and data collection time interval of 2 hours, to both the Chukwooki and the modern data. Annual maximum rainfall event series were then constructed, by applying Freund's bivariate exponential distribution annually. Finally, bivariate frequency analysis was done for the annual maximum rainfall event series constructed, by applying the bivariate logistic model to evaluate and quantify their characteristics. The results are in summary: (1) characteristics of the Chukwooki rainfall events and modern rainfall events are very similar to each other; (2) the annual maximum rainfall events of modern data are slightly larger than those of the Chukwooki data. The total rainfall depth per rainfall event for any given return period is thus estimated to be a little higher for the modern data than that of the Chukwooki data. However, based on the findings in this study, it could not be concluded that the rainfall characteristics have significantly changed during the last 200 years.

Divergent responses of vegetation aboveground net primary productivity to rainfall pulses in the Inner Mongolian Plateau, China

The differential responses of vegetation types to rainfall pulses are still not fully understood in the Inner Mongolian Plateau. This study firstly investigated the hierarchical responses of vegetation aboveground net primary productivity (ANPP) to rainfall pulses in the Inner Mongolian Plateau using Normalized Difference Vegetation Index (NDVI) as a proxy. Forty-eight independent rainfall events were selected between 2000 and 2013 for three study sites within a precipitation gradient transect. Results of the threshold-delay model revealed that vegetation in the Gobi desert and Typical steppe responded much faster with 3.6 ± 2.0 day and 6.4 ± 4.6 day, respectively, contrast with a durable response in Desert steppe (10.2 ± 6.5 day). Desert steppe had the highest upper threshold of rainfall (80.2 mm), which was about two-fold of Gobi desert (36.1 mm) and Typical steppe (41.2 mm). Pulse size, timing, soil texture and plant functional type (PFT) were the main drivers that influenced the rate and magnitude of vegetation responses. The results highlight the differential responses of vegetation types to rainfall pulses in the Inner Mongolian Plateau and may contribute to a better understanding of the impact of changing rainfall patterns on vegetation dynamics in arid and semiarid regions.

레이더 자료를 이용한 호우의 산지효과 특성 분석:충주댐 유역을 대상으로

This study analyzed the characteristics of orographic effect using radar data for the Chungju dam basin. First, independent rainfall events were selected by applying the IETD (Interevent Time Definition) and rainfall threshold. Among those independent rainfall events, rather strong events were selected to decide the occurrence condition of orographic effect. Also, the average reflectivity was calculated for the entire period and for the period of storm center, and the change in reflectivity was analyzed by comparing the average reflectivity to that in the mountain area. Important rainfall factors were selected and applied to the logistic regression model to decide the occurrence condition of orographic effect. Summarizing the results is as follows. First, evaluation of the radar data along the passing line of a storm showed the increase of radar reflectivity in the mountain area. Second, the result of logistic regression analysis showed that the orographic effect in the Chungju Dam Basin mostly occurred when the rainfall intensity was higher than 4 mm/hr, the storm velocity was lower than 4 km/hr, and the approach angle was .

Minimum Inter-Event Time to Identify Independent Rainfall Events in Urban Catchment Scale

For many hydrologic analyses, planning or design problems, reliable rainfall estimates are necessary. For this reason, an accurate estimation of storm event properties is central to continuous simulation of rainfall. Rainfall is generally noted as single events or storms where the beginning and the end are defined by rainless of particular size duration called Minimum Inter-event Time (MIT). Starting from a critical study of the state of the art, this paper intends to investigate the definition of MIT for rainfall events shorter than an hour that, on an urban scale, are the most critical for designers, planners and operators of urban drainage system. All event characteristics such as depth and mean rain rate, are influenced by the choice of the value of MIT. This paper reviews the range of approaches used in literature and after this, based on a year of pluviograph records on an urban catchment, proposes a value of MIT according to catchment network entry time.

Wyznaczenie opadów deszczu statystycznie niezależnych na podstawie danych pomiarowych

Wyznaczenie opadów deszczu statystycznie niezależnych na podstawie danych pomiarowych

Empirical regression models for estimating nitrogen removal in a stormwater wetland during dry and wet days

Due to the highly variable hydrologic quantity and quality of stormwater runoff, which requires more complex models for proper prediction of treatment, a relatively few and site-specific models for stormwater wetlands have been developed. In this study, regression models based on extensive operational data and wastewater wetlands were adapted to a stormwater wetland receiving both base flow and storm flow from an agricultural area. The models were calibrated in Excel Solver using 15 sets of operational data gathered from random sampling during dry days. The calibrated models were then applied to 20 sets of event mean concentration data from composite sampling during 20 independent rainfall events. For dry days, the models estimated effluent concentrations of nitrogen species that were close to the measured values. However, overestimations during wet days were made for NH(3)-N and total Kjeldahl nitrogen, which resulted from higher hydraulic loading rates and influent nitrogen concentrations during storm flows. The results showed that biological nitrification and denitrification was the major nitrogen removal mechanism during dry days. Meanwhile, during wet days, the prevailing aerobic conditions decreased the denitrification capacity of the wetland, and sedimentation of particulate organic nitrogen and particle-associated forms of nitrogen was increased.

호우사상의 시간적 정량화를 위한 베타분포의 적용

본 연구에서는 주어진 호우사상을 베타분포로 적절히 표현하기 위한 매개변수의 결정 방법을 제시하였다. 이를 위해 첨두에 대한 고려를 추가한 경우와 그렇지 않은 경우, 실제 우량주상도 및 첨두를 중심으로 재배열된 수정 우량주상도를 사용하는 경우 등을 고려하여 그 특성을 비교 검토하였다. 본 연구는 서울 지점의 2010년 독립 호우사상과 1961~2010년 사이의 연 최대치 독립 호우사상을 대상으로 베타분포를 적용하고, 그 결과를 분석하였다. 그 결과를 정리하면 다음과 같다. 첫째, 베타분포를 이용하여 실제 호우사상의 우량주상도 형태를 유사하게 표현하기 위해서는 첨두에 대한 추가적인 고려가 필요한 것으로 확인되었다. 둘째, 첨두를 중심으로 시간강우를 좌우 순차적으로 재배열한 수정 우량주 상도를 이용하는 경우가 실제 우량주상도를 이용하는 경우보다 실제 강우의 시간분포 특성에 보다 가까운 베타분포를 유도함을 확인하였다. This study suggested the parameter estimation method for given rainfall events to be properly expressed by the beta distribution. For this purpose, this study compared the characteristics of probability density function with the parameter proposed considering the cases with and without addition to the rainfall peak, and the cases of using the real hyetograph and the rearranged hyetograph about the rainfall peak. As an example, this study analyzed the independent rainfall events at Seoul in 2010 and the annual maximum independent rainfall events from 1961 to 2010. The results derived are as follows. First, this study confirmed the necessity of additional consideration on rainfall peak to mimic the real hyetograph of rainfall events by the beta distribution. Second, this study confirmed the case of using rearranged hyetograph about the rainfall peak derived a better beta distribution to well mimic the characteristics of real rainfall than the case using the real hyetograph.

연최대치 계열과 연최대치 독립 호우사상 계열의 비교

본 연구에서는 강우 지속기간이 짧은 경우와 긴 경우에 대한 연최대치 계열과 연최대치 독립 호우사상 계열의 차이를 살펴보았다. 연최대치 독립호우사상은 1961년부터 2010년까지의 서울지점 시강우 자료에 다양한 IETD와 절단값을 적용하여 추출하였다. 결정된 연최대치 독립호우사상 계열은 기존의 연최대치 계열과 비교하였다. 그 결과를 요약하면 다음과 같다. 첫째, IETD와 절단값의 영향은 예상할 수 있는 수준을 벗어나지 않았다. 예를 들어, IETD의 증가에 따라 짧은 지속기간 및 긴 지속기간을 갖는 독립 호우사상의 발생 빈도는 유사한 감소비율을 갖으나, 절단값의 증가에 따라서는 특히 지속기간이 긴 호우사상의 발생빈도가 급격히 감소하는 것으로 나타났다. 둘째, 추출된 독립 호우사상의 평균 강우강도는 강우 지속기간에 관계없이 거의 일정한 것으로 나타났다. 이는 연 최대치 강우강도가 주로 지속기간이 긴 호우사상에서 결정될 가능성이 크다는 것을 의미한다. 마지막으로, 강우지속기간이 짧은 경우, 연 최대치 계열과 연 최대치 독립 호우사상 계열의 차이가 매우 큰 것으로 확인되었다. 그러나 이러한 차이는 강우 지속기간이 증가함에 따라 현저히 줄어들었다. 이러한 결과는 특히 매우 짧은 집중시간을 고려하는 작은 유역의 경우, 전통적인 자료 분석방법을 통해 결정된 설계강우가 실제 발생 가능성이 없는 비현실적인 경우가 될 가능성이 매우 큼을 의미한다. This study investigated the differences between annual maximum series and annual maximum independent rainfall event series with relatively short and long rainfall durations. Annual maximum independent rainfall events were selected by applying various IETDs and thresholds to the hourly rainfall data in Seoul for the duration from 1961 to 2010. Annual maximum independent rainfall event series decided were then compared with the conventional annual maximum series. Summarizing the results is as follows. First, the effect of IETD and threshold was not beyond the expected level. For example, as the IETD increases, the frequencies of independent rainfall events decreased similarly in their rate for both with short and long durations. However, as the threshold increases, the frequency of those with rather long durations decreased much higher. Second, The mean rainfall intensity of the independent rainfall events was found to remain constant regardless of their duration. This indicates that the annual maximum rainfall intensity could be found in a rainfall event with longer durations. Lastly, the difference between the annual maximum rainfall series and the annual maximum independent rainfall event series with rather short rainfall durations was found significantly large, which decreases with longer durations. This result indicates that the conventional data analysis method, especially for small basins with short concentration time, could lead an unrealistic design rainfall with little possibility of occurrence.

Comparative Case Study of Rainfall-Runoff Modeling between SWMM and Fuzzy Logic Approach

A comprehensive hydrological model, like the storm water management model (SWMM), has been widely used for rainfall-runoff simulation. In recent years, simple and effective modern modeling techniques have also brought great attention to the prediction of runoff with rainfall input. A comparative case study between SWMM and a presently developed fuzzy logic model for the predictions of total runoff within the watershed of Cascina Scala, Pavia in Italy is presented. A data set of 23 events from 2000 to 2003 including with the total rainfall and total runoff are adopted to train fuzzy logic parameters. Other data (1990–1995) with detailed time variations of rainfall and runoff are available for the setup and calibration of SWMM for runoff modeling. Among the 1990–1995 data, 35 independent rainfall events are selected to test the prediction performance of the SWMM and fuzzy logic models by comparing the predicted total runoffs with measured data. Comparisons and performance analyses in terms of the root-mean-squared error and coefficient of efficiency are made between the SWMM and the fuzzy logic model. The predicted total runoffs from either the SWMM or the fuzzy logic model are found to agree reasonably well with the measured data. For large rainfall events, the fuzzy logic model generally outperforms the SWMM unless the modification of the impervious ratio is applied to improve the SWMM results. However, the SWMM can produce the time varying hydrograph whereas fuzzy logic is subject to limitation of the methodology and is unable to generate such an output.

유역 및 기상상태를 고려한 Clark 단위도의 매개변수 평가: 2. 매개변수의 변동성 추정

본 연구에서는 Clark 합성단위도의 매개변수 추정치에 대한 신뢰구간을 좁힐 수 있는 방안으로, 이들을 강우, 기상, 및 유역 특성인자로 다변량 회귀분석한 후 이를 Monte Carlo 모의기법을 통하여 분석하였다. 아울러 이렇게 얻은 결과는 Bootstrap 기법으로 분석한 결과 및 기존에 많이 사용되어 왔던 경험식과도 비교 검토하였다. 이상과 같은 과정을 통해 얻은 결과는 다음과 같다. (1) 관측된 호우사상의 수가 제한적인 경우, 유출특성에 미치는 인자들을 복합적으로 고려하여 유역의 평균유출특성을 추정하는 것이 가능하다. (2) Monte Carlo 모의기법을 적용하여 추정된 집중시간 및 저류상수의 신뢰도 평가가 가능하다. 이렇게 추정한 신뢰구간은 유철상 등(2006)에서의 신뢰구간에 비해 훨씬 좁은 것으로 파악되었다. (3) Bootstrap을 통한 관측자료의 분석에서도 위의 결과를 지지하는 결론을 얻을 수 있었다. 그러나 어느 정도 신뢰도 있는 집중시간 및 저류상수의 추정을 위해서는 최소 20개 정도 이상의 독립된 호우사상이 필요할 것으로 파악되었다. (4) 기존의 경험공식과의 비교에서는 어떤 공식도 본 유역의 유출특성을 잘 대변하지는 못하는 것으로 파악되었다. 그러나 집중시간의 경우 Kraven(I)과 Kraven(II)이 저류상수의 경우 Linsley 공식이 유사한 값을 주는 것으로 나타났다. 그러나 이 값 역시 상한과 하한의 범위에 크므로 사용 시 주의할 필요가 있음을 파악할 수 있었다. In this study, as a method for decreasing the confidence interval of the estimates of Clark hydrograph's concentration time and storage coefficient, regression equations of these parameters with respect to those of rainfall, meteorology, and basin characteristics are derived and analyzed using the Monte Carlo simulation technique. The results are also reviewed by comparing them with those derived by applying the Bootstrap technique and empirical equations. Results derived from this research are summarized as follows. (1) Even in case of limited rainfall events are available, it is possible to estimate the mean runoff characteristics by considering the affecting factors to runoff characteristics. (2) It is also possible to use the Monte Carlo simulation technique for estimating and evaluating the confidence intervals for concentration time and storage coefficient. The confidence intervals estimated in this study were found much narrower than those of Yoo et al. (2006). (3) A supporting result could also be derived using the Bootstrap technique. However, at least 20 independent rainfall events are necessary to get a rather significant result for concentration time and storage coefficient. (4) No empirical equations are found to be properly applicable for the study basin. However, empirical equations like the Kraven(I) and Kraven(II) are found valid for the estimation of concentration time, on the other hand the Linsley is found valid for the storage coefficient In this study basin. But users of these empirical formula should be careful as these also provide a wide range of possible values.