• Journal of Wetlands Research
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• v.6 no.4
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• pp.35-43
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• 2004

The non-parametric Mann-Kendall(MK) statistical test has been widely used to assess the significance of trend in hydrologic time series. The test requires sample data should be serially independent. If sample data is serially correlated, the presence of serial correlation in a time series will affect the test ability for trend analysis. So, we would like to use the modified MK test which uses the effective sample size(ESS) to eliminate the effect of serial correlation in a series. This study investigates the ability of ESS to eliminate the influence of serial correlation of MK test by Monte Carlo simulation and by real series. As the results, MK test shows the increase of trend rate as the serial correlation is increased but the modified MK test shows ESS can eliminate the serial correlation for trend analysis. Therefore we confirmed the modified MK test is a very useful tool for trend analysis.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.153-153
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• 2012

기후변화는 강우량, 기온, 해수면온도 등 많은 수문기상학적 요소에 영향을 끼치고 있으며 이러한 영향에 대한 연구가 활발하게 진행되고 있다. 그 중에서도 수공구조물의 설계에 직접적으로 영향을 끼치는 강우특성에 대한 연구는 기후변화로 야기되는 강우의 비정상성(non-stationary)을 중심으로 이루어지고 있다. 현재 수문설계량은 강우량의 빈도해석을 통해 산정되는데, 이러한 빈도해석은 기본적으로 연최대강우자료의 정상성(stationary)과 독립성(independent)을 가정하고 이루어진다. 그러나 기후변화로 연최대강우자료에 경향성이나 변동성이 나타남에 따라 경향성과 변동성을 고려할 수 있는 빈도해석 기법의 개발에 대한 필요성이 증가하고, 실제로 2000년대에 들어서면서부터 우리나라뿐만 아니라 전 세계적으로 이루어지고 있다. 연최대강우자료의 정상성을 판단하기 위해 강우자료에 대한 경향성 분석을 수행하게 되는데, 경향성 분석을 위해 다양한 통계적 기법들이 적용되고 있다. 그러나 현재 경향성 분석방법의 적용에 대한 뚜렷한 기준이 없어 여러 가지의 경향성 분석 방법을 적용하여 다수의 분석방법별 결과를 종합하여 경향성 유무를 판단하고 있는 실정이며, 동일자료에 대해서도 연구에 따라 다른 결과가 나타나고 있다. 따라서 본 연구에서는 경향성 분석방법의 기각력을 비교검토하여 경향성 분석방법의 적용에 필요한 기준을 제시하고자 한다. 이를 위해 경향성 분석을 위해 널리 사용되고 있는 t-test, Mann-Kendall test, Hotelling-Pabst test를 비교하고자 한다. 여기에서 t-test는 매개변수를 사용하는 매개변수적 방법이고, Mann-Kendall test와 Hotelling-Pabst test는 비매개변수적 방법이다. 귀무가설의 경우 t-test는 경향성이 없다고 가정하고 있는데 반해, Mann-Kendall test와 Hotelling-Pabst test는 경향성이 있다고 가정하고 있다. 기각력 검토를 위해서는 Monte Carlo simulation을 이용하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3B
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• pp.295-303
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• 2010

The variability of vegetation is strongly related to the variability of hydrometeorological factors such as precipitation, temperature, runoff and so on. Analysis of the variability of vegetation will aid to understand the regional impact of climate change. Thus we analyzed the spatial-temporal variability of NOAA(National Oceanic and Atmospheric Administration)/AVHRR(Advanced Very High Resolution Radiometer) NDVI(Normalized Difference Vegetation Index). In the results from Mann-Kendall test, there is no significant linear trend of annual NDVI from 1982 to 2006 in the most area except the downward trend on the significance level 90% in the Guem-river basin area. In addition, using EOF(Empirical Orthogonal Function) analysis, the variability of NDVI in the region of higher latitude and altitude is higher than that in the other region since the spatial variability of NDVI follows the latitudinal gradient. Also we could get higher NDVI in June, July, August and September. We had the highest NDVI in Han-river basin area and the lowest in Je-Ju island.

• Journal of The Korean Society of Agricultural Engineers
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• v.66 no.2
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• pp.25-34
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• 2024

The long-term monitoring of the Soyang Lake's water quality, covering 25% of the North Han River watershed, is crucial for effective management of both lake water quality and pollution sources in the broader region. This study utilized continuous monitoring data from the front of the Soyang Dam spanning 2003 to 2022, aiming to analyze trends and provide foundational insights for water quality management. Results revealed a slightly poor grade (IV) for total nitrogen (T-N) in both surface and mid-depth layers, indicating a need for concentrated T-N management. Trend analyses using the Mann-Kendall test and Sen's Slope depicted a decreasing trend in total phosphorus (T-P) for both layers, attributed to non-point source pollution reduction projects initiated after the Soyang Lake's designation as a pollution control area in 2007. The LOWESS analysis showed a T-P increase until 2006, followed by a decrease, influenced by the impact of Typhoon Ewiniar in that year. This 20-year overview establishes a comprehensive understanding of the Soyang Lake's water quality and trends, allowing for a seasonal and periodical analysis of water quality changes. The findings underscore the importance of continued monitoring and management strategies to address evolving water quality issues in the Soyang Lake over time.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.12
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• pp.1225-1230
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• 2008

A new approach based on the Seasonal Mann-Kendall Trend Analysis, was presented in this paper, in order to estimate effect of water quality management policy in Kyoungan Stream which is one of major tributaries into the Lake Paldang. The estimation was undertaken by comparing water quality trend slopes before and after implementation of the policy. The monthly water quality data of Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Nitrogen (TN) and Total Phosphorus (TP) measured from 1992 to 2005, were analyzed to determine the Kendall slopes before and after the Han River special policy implemented at 1998. The results indicated that the 1998 special policy would be effective in water quality improvement not at upstream but at downstream. This result agrees well with the previous water quality studies at Kyoungan stream. It was suggested that the presented approach could be an useful tool to estimate effect of a water quality management policy.

• Journal of Korean Society of Water and Wastewater
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• v.22 no.1
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• pp.23-29
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• 2008

Throughout the analysis of field data from water distribution system, valid parameters were determined that can be included in the water service and design plan. This study investigates water consumption patterns to understand the variation of water-demand structures utilizing the pattern analysis of domestic purpose water. Water use data were collected by a public water resources management firm in Korea, Kwater, for 140 houses monitored during three years. Flow meters were installed at the faucet for drinking water, the shower booth, the laundry machine, bathroom sink, toilet, and garden faucet. Data was filtered using multiple physically meaningful criteria to improve analysis credibility. Mann Kendall and Spearman's Rho tests were used to carry out the analysis. Distinct factors of water consumption patterns can be determined for both increasing and decreasing trends of water use. Throughout the data analysis, the characterization of terms was classified and analyzed by the condition of the location of water-demand. Analysis of this data provide a physical basis for the parameter configuration of a reasonable design for a domestic water demand prediction model.

• Journal of Korean Society on Water Environment
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• v.20 no.1
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• pp.63-71
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• 2004

The long-tenn trend analyses of water qualities were performed for 49 monitoring stations located in Nakdong River. Water quality parameters used in this study are the monthly data of BOD(Biological Oxygen Demand), TN(Total Nitrogen) and TP(Total Phosphorus) measured from 1990 to 1999. The long-tenn trends were analyzed by Seasonal Mann-Kendall Test and Locally WEighted Scatter plot Smoother(LOWESS). Nakdong river was divided into four subbasins, including upstream watershed, midstream watershed, western downstream watershed and eastern downstream watershed. The results of Seasonal Mann-Kendall Test indicated that there would be no trends of BOD in upstream watershed, western and eastern downstream watershed. Trends of BOD were downward in midstream watershed. For TN and TP, there were upward trends in all of watersheds. But LOWESS curves suggested that BOD, TN and TP concentrations generally increased between 1990 and 1996, then resumed decreasing.

• Current Research on Agriculture and Life Sciences
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• v.32 no.3
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• pp.135-143
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• 2014

The variability and temporal trends of the annual and seasonal minimum and maximum temperature, rainfall, relative humidity, wind speed, sunshine hours, and runoff were analyzed for 5 major rivers in Korea from 1960 to 2010. A simple regression and non-parametric methods (Mann-Kendall test and Sen's estimator) were used in this study. The analysis results show that the minimum temperature ($T_{min}$) had a higher increasing trend than the maximum temperature ($T_{max}$), and the average temperature increased by about $0.03^{\circ}C\;yr.^{-1}$. The relative humidity and wind speed decreased by $0.02%\;yr^{-1}$ and $0.01m\;s^{-1}yr^{-1}$, respectively. With the exception of the Han River basin, the regression analysis and Mann-Kendall and Sen results failed to detect trends for the runoff and rainfall over the study period. Rapid land use changes were linked to the increase in the runoff in the Han River basin. The sensitivity of the evapotranspiration and ultimately the runoff to the meteorological variables was in the order of relative humidity > sunshine duration > wind speed > $T_{max}$ > $T_{min}$. Future studies should investigate the interaction of the variables analyzed herein, and their relative contributions to the runoff trends.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.193-193
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• 2017

Trend analysis can enhance our knowledge of the dominant processes in the area and contribute to the analysis of future climate projections. The results of previous studies in South Korea showed that southeast regions of Korea had the highest value of evapotranspiration. Thereby, it is of interest to determine the trend analysis in hydrological variables in this area. In this study, the recent 35 year trends of precipitation, reference evapotranspiration, and aridity index in monthly and annual time scale will be analyzed over three stations (Pohang, Daegu, and Pusan) of southeast Korea. After removing the significant Lag-1 serial correlation effect by pre-whitening, non-parametric statistical Mann-Kendall test was used to detect the trends. Also, the slope of trend of the Mann-Kendall test was determined by using Theil-Sen's estimator. The results of the trend analysis of reference evapotranspiration on the annual scale showed the increasing trend for the three mentioned stations, with significant increasing trend for Pusan station. The results obtained from this research can guide development if water management practices and cropping systems in the area that rely on this weather stations. The approaches use and the models fitted in this study can serve as a demonstration of how a time series trend can be analyzed.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.141-141
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• 2020

강원도는 산림 비중이 크고 급경사지가 많은 지형적 특성과 여름철 비교적 선선하고 강우량이 많은 기후적 특성 때문에 고랭지 농업이 활발히 이루어지고 있다. 하지만, 많은 부분을 차지하는 고랭지밭 면적 탓에 강우시에 토양침식과 비점오염물이 하천으로 유입되고 있다. 강원도 송천 상류에 위치한 도암호는 장기간 탁수를 저류하고 방류로 인한 해체 논란까지 일으키기도 했다. 이에 정부는 흙탕물 저감과 비점오염원 관리를 위한 국고보조사업과 다양한 환경 정책들을 시행중이다. 효율적이고 효과적인 수질 정책을 시행하고 분석하기 위해서는 장기간의 모니터링 자료를 이용한 통계적 분석을 활용하는 것이 중요하다. 수질 자료는 변동이 심하고, 비정규분포를 이루며 결측치와 검출한계 이하의 값들이 많아 비모수 통계 방법을 널리 사용되어 왔다. 그중에서도 계절적 특성을 갖는 수질자료의 장기경향분석에 적합한 Seasonal Mann-Kendall Test을 사용하여 남한강상류 유역의 수질 경향성을 분석하였으며, Sen's Slope를 구하여 수질 자료의 경향 크기를 구하였다. 하지만, Seasonal Mann-Kendall Test는 연구 기간동안의 경향성을 반영할 수 없다는 단점이 있기 때문에 LOWESS Test를 통해 장기간 수질 자료 사이의 경향성을 분석하였다. 이러한 수질자료의 경향 분석 결과는 유역 내 취약 지점을 확인할 수 있으며, 환경 정책의 효과를 평가하고 보완할 수 있는 자료로 이용될 수 있을 것이다.