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Meteorological drought is a continuous spatiotemporal phenomenon that poses a serious threat to water resource security. Dynamic evolution and multivariable frequency analysis of meteorological drought are important for effective drought mitigation and risk management. Therefore, this study aims to analyze meteorological drought events in northwestern China between 1960 and 2018 based on the standardized precipitation evapotranspiration index (SPEI) through a three-dimensional identification method. This study investigates the meteorological drought dynamic evolution on different time and space scales and evaluates the frequency analysis considering the spatiotemporal variability based on Copula. The results show that SPEI presents an upward trend in Northwestern China. A trend towards increased humidity is observed in arid regions, contrasted by a trend towards aridification in semi-arid and semi-humid areas, indicating that the spatial distribution of drought in the study area tends towards homogenization. The possibility of high-intensity drought events occurring in the same area was relatively low, whereas low-intensity drought events were frequent. Additionally, this study analyzes the dynamic migration process of individual drought events from a three-dimensional perspective. Neglecting any one drought variable could significantly underestimate the occurring probability of severe drought events. Therefore, a multivariable frequency analysis considering the spatiotemporal variability plays a crucial role in the formulation of drought prevention and mitigation strategies, as well as drought forecasting. [ABSTRACT FROM AUTHOR]

Purpose: With the rapid development of urban metro systems in the growing cities of China, a way to reduce metro train-induced track vibrations transmitted through ground to surrounding buildings has attracted the attention of engineering researchers. Using additional mass, damping and flexural stiffness to improve the dynamic performance of metro tracks, a Tuned Rail Damper (TRD) is developed to mitigate the vibrations of the metro tracks. Methods: In this paper, a laboratory hammer test is designed and carried out to assess the vibration performance of a 3-interval (of 3 × 0.6 m) metro track installed with the TRD sets. Results: The hammer test results indicated that depending on the position of a hammer impulse acting on the 3-interval track unit, different excitation frequencies would be measured. Conclusion: According to the experimental study, the TRD has advantages such as easy installation, convenient inspection by hammer test, and good vibration reduction performance for its flexural strengthening effect on metro tracks. Moreover, the composed TRD-track system has a robust ability to reduce vibrations and an increase of higher frequencies compared to conventional tracks. This dynamic feature can decrease the risk of clip failure in a fastening system subjected to intensive excitations from moving metro trains. [ABSTRACT FROM AUTHOR]

The probability of a train running over a bridge when an earthquake occurs is increasing with the total mileage of China's high-speed railway network expanding. To study this issue, a three-dimensional train-track-bridge dynamic interaction system subjected to seismic excitations is established based on commercial mathematical software. Besides, a set of motion equations of the system are derived according to the multibody dynamics, the finite element method theory and the bridge seismic theory. Moreover, in order to study the dynamic response of high-speed railway bridges under earthquake, a series of experiments are conducted on a scaled high-speed railway simple supported bridge model with a ballastless track slab excited by shaking table tests. Meanwhile, the strain of rails, track slabs, base plates and girder in various working conditions are measured by quasi-distributed optical fiber sensing stuck in bridge members. At last, the dynamic response of each structure member is demonstrated in the time and frequency domains. Furthermore, the seismic isolation performance of bridge members, such as fasteners, cement asphalt (CA) mortar layer and so on, is explained in details. [ABSTRACT FROM AUTHOR]

Late frost is one of the most destructive meteorological disasters in the Loess Plateau of China. A great threat can be posed to the sustainable production of apples, leading to great economic losses in the apple industry. Thus, it is a high demand to explore the occurrence of late frost events for the prevention of apple late frost disasters in the decision-making of the local apple industry. In this study, the late frost return periods were investigated on the duration and severity of late frost events using the Coupla functions. The reliability of the model was then verified to analyze the characteristics of apple late frost. The study area was taken as the apple-producing areas of Shaanxi Province in western China. The meteorological datasets were collected from the seven weather stations from 1971-2018. The daily minimum temperature (Tmin) of 0℃ was taken as the critical temperature for the occurrence of apple late frost events, in order to extract the two characteristic variables of duration and severity of late frost events. These characteristic variables of late frost events were first fitted by seven common distribution functions, respectively. Kolmogorov Smirnov (K-S) test was then carried out to verify the model. The joint distributions of late frost characteristic variables were constructed to evaluate the goodness-of-fit using six Copula functions. The occurrence probability and return period of late frost events were analyzed with the optimized Copula functions. The results showed that the severity of late frost risks generally increased from the southeast to northwest in the study area from 1971 to 2018. The optimal marginal distribution of late frost duration was in the log-normal distribution, while there was a great difference in the optimal marginal distributions of late frost severity. A significant positive correlation was found between the duration variables and the severity of late frost at each station. The goodness-of-fit test demonstrated that most of the stations presented the optimal distribution of Normal Copula function for late frost events. The joint cumulative probability increased significantly, as the severity and duration of late frost increased, but the increasing trend was much slower than before. A much more significant increase was observed in the co-occurrence return period under the same increase of univariate value, compared with the joint. The univariate return period was always between the joint and co-occurrence return period. Once the univariate return period was small enough, the optimal range of the actual univariate return period can be estimated, according to the joint and the co-occurrence return period. In general, a low probability was found in the late frost events with long duration and high severity at the weather stations in apple-producing areas in Shaanxi Province of China. However, the stations in the Yan’an area were more susceptible to the late frost events with high severity or long duration, as well as the late frost events with both high severity and long duration. Thus, more attention can be paid to late frost risks in the Yan’an area. This finding can provide a theoretical base to deal with the late frost disaster in apple production. [ABSTRACT FROM AUTHOR]

Multivariate hydrological frequency analysis is important when designing hydraulic and civil infrastructures. However, hydrologic data scarcity and insufficiency are common. By studying the relationship between copula entropy and total correlation estimated by the matrix-based Renyi's α-order entropy functional, a new estimation method (total correlation estimation, TCE) for parameters of the Gumbel-Hougaard copula and Clayton copula was proposed when the sample size was equal to or less than 30. A total of 11,802 simulations were performed to evaluate the performance of TCE for sample sizes ranging from 30 to 5, and were compared with traditional estimation methods that require a large amount of data. As for the Gumbel-Hougaard copula, the performance of TCE is satisfactory regardless of sample size, while the traditional methods perform poorly when the sample size is equal to or less than 20. For the Clayton copula, TCE is reliable and robust and performs well if the sample size is greater than 10, while the traditional methods are unreliable when the sample size is less than 25. Also, TCE is applied to construct the joint distributions of annual runoff and sediment discharge in the Xiliugou River, China. The method based on Renyi's α-order entropy functional provides a new way for multivariate hydrological frequency analysis with small sample sizes. [ABSTRACT FROM AUTHOR]

Focusing on FinTech keywords, this study is analyzing newspaper articles and Twitter data by using text mining methodology in order to understand trends in the industry of domestic digital financial service. In the growth of FinTech lifecycle, the frequency analysis has been performed by four important points: Mobile Payment Service, Internet Primary Bank, Data 3 Act, MyData Businesses. Utilizing frequency analysis, which combines the keywords ‘China’, ‘USA’, and ‘Future’ with the ‘FinTech’, has been predicting the FinTech industry regarding of the current and future position. Next, sentiment analysis was conducted on Twitter to quantify consumers' expectations and concerns about FinTech services. Therefore, this study is able to share meaningful perspective in that it presented strategic directions that the government and companies can use to understanding future FinTech market by combining frequency analysis and sentiment analysis. [ABSTRACT FROM AUTHOR]

The construction of check dams in northwestern China has resulted in nonstationary changes in flood peak discharge series; the stationary assumption of the conventional hydrological frequency analysis is no longer satisfied. According to the characteristics of the construction and operation of check dams, the nonstationarity of flood peak discharge series are largely induced by changes in the effective runoff generation area (i.e., the basin area minus the area controlled by check dams). Knowing the power function relationship between the flood peak discharge and the basin area, we can remove the influence of the effective runoff generation area and convert the original nonstationary series into a stationary series. This de-nonstationarity method can achieve stationarity in the first and second moments simultaneously. Therefore, we can calculate the design value of the reconstructed series using the conventional frequency analysis method. According to the effective runoff generation area under design conditions, we can then obtain the corresponding design flood of the original series. We applied this method to the Mahuyu River basin to obtain the design flood under nonstationarity. Due to the consideration of the deterministic influence of check dams during the de-nonstationarity process, the uncertainty analyzed by the bootstrap method is obviously small. [ABSTRACT FROM AUTHOR]

The application of traditional urea usually causes low efficiency of nutrient utilization, and environmental pollution, due to the excessive use of fertilizers, and mismatching between the nutrient release stage of fertilizers and the growth stage of crops. The controlled-release fertilizer, serving as a promising new fertilizer, can be used to improve nutrient use efficiency and crop yields via adjusting the stage of nutrient release. The objective of this study was therefore to explore the effects of controlled-release fertilizers in different release periods, and the nitrogen levels in irrigation water on winter wheat yield. A field experiment was conducted in the Modern Agriculture Demonstration Park, Wugong Town, Xianyang City, Shaanxi Province, China. The optimum combinations of water and fertilizer inputs were determined for both single-objective and multi-objective optimizations through the frequency and multiple regression analysis method. The main, sub, and sub-sub plots were designed in the field experiments. In the main zone plots, three irrigation levels were set as W1 (30 mm), W2 (60 mm), and W3 (90 mm). The sub plots comprised of four nitrogen fertilization levels, including N0 (0 kg/hm²), N1 (75 kg/hm²), N2 (150 kg/hm²), and N3 (225 kg/hm²). The sub-sub plots included three different nitrogen fertilizer types, namely PCU60 (a controlled-release fertilizer with a release periods of 60 days), PCU120 (a controlled-release fertilizer with a release periods of 120 days), and U (traditional urea). A controlled release fertilizer was applied at one time during planting, where the application mode of traditional nitrogen fertilizer (U) as a control. The effect of water and nitrogen dosage on winter wheat yield was clarified under the condition of controlled-release fertilizer, thereby to propose the optimal range of water and fertilizer dosage in various fertilizers. The results showed that the amount of irrigation water, nitrogen application rates, and different types of controlled-release fertilizer had significant effects on the spike number, grain number per spike, 1000-kernal mass, amount of dry matte, and grain yield of winter wheat. The interaction between two factors also had a significant impact on the grain yield. In the same irrigation levels, the winter wheat yield increased first, and then decreased with increasing nitrogen fertilizer application levels, where the maximum was obtained when the application rate of nitrogen fertilizer was 150 kg/hm². In the same nitrogen fertilizer levels, the winter wheat yield increased first, and then decreased with increasing the irrigation levels, where the maximum was achieved, when the irrigation level was 60 mm. The interaction effect between the type of controlled release fertilizer and the amount of irrigation/nitrogen application showed that: compared with the U treatment, with the increase of irrigation levels, the average yield of PCU60 increased by 308 kg/hm², and PCU120 decreased by 270 kg/hm²; on the contrary, with the increase of nitrogen application rates, the average yield of PCU60 decreased by 289 kg/hm², and PCU120 increased by 118 kg/hm². According to the water and nitrogen production functions of three fertilizers, the yield-increasing effects of two controlled-release fertilizers were 14.31% (PCU120) and 12.08% (PCU60), respectively, under the water and nitrogen application when the U achieved the highest theoretical yield of 6 823 kg/hm². In a frequency analysis, the most appropriate ranges of water and nitrogen for different fertilizer types were: 67.20-70.22 mm and 145.42-187.91 kg/hm² under the PCU60 fertilizer treatment; 47.72-52.28 mm and 159.23-199.47 kg/hm² under the PCU120 fertilizer treatment; 77.51-79.99 mm and 167.55-207.45 kg/hm² under the U treatment. The yield-increasing ranges were 7 647-7 719 kg/hm² (PCU60), 7 744-7 906 kg/hm² (PCU120), and 6 733-6 823 kg/hm² (U) under the most appropriate ranges of water and nitrogen application for different fertilizer types, respectively. Therefore, it can be recommended that an optimal irrigation level (47.72-52.28 mm) and fertilizer application (PCU120, 159.23-199.47 kg/hm²) ranges can be considered as the best water and fertilizer management strategy for maximizing water-fertilizer productivity of winter wheat. [ABSTRACT FROM AUTHOR]

To meet flood control demand, many reservoirs have been built successively in China for many years. Reservoir inflow synchronization analysis for multiple reservoirs in the flood season can provide a reference for the formulation of the joint water supply operation plan and improve the utilization efficiency of water resources. In this paper, a two-dimensional copula model is used to analyze the reservoir inflow synchronization between a single reservoir on a tributary and the reservoir on the mainstream of the river in the flood season. Based on the obtained results, a R-vine copula model is established by selecting a suitable structure to analyze the multidimensional joint reservoir inflow synchronization for multiple reservoirs in the middle and lower reaches of the Yellow River basin in the flood season. For four selected reservoirs in the middle and lower reaches of the Yellow River basin in China as a case study, the frequencies of synchronous wetness and synchronous dryness for the four reservoirs are 15.106% and 15.209%, respectively. The research results can serve as a reference for actual scheduling. [ABSTRACT FROM AUTHOR]

Rural revitalization strategy is a hot topic in China. How to ensure the steady advancement of rural revitalization strategy and its effect of rural revitalization needs to evaluate the level of rural revitalization. Therefore, Construction of a scientific and reasonable evaluation index system for rural rejuvenation level is of great significance for the monitoring and evaluation of rural rejuvenation level. This study uses five aspects indexes of prosperity of industry, ecological livability, rural civilization, effective governance, and wealthy life to construct a evaluation index system of rural revitalization level based on statistical analysis of the evaluation indexes in the literature and frequency analysis, combined with expert consultation and field surveys, and the indexes are comprehensive grain production capacity; agricultural science and technology progress contribution rate; agricultural labor productivity; proportion of agricultural mechanization; level of agricultural informatization; village green coverage; waste treatment rate; rural sanitary toilet penetration rate; days of air quality compliance;percentage of expenditure on education, culture and entertainment of rural residents; average years of education of rural population; proportion of full-time teachers with bachelor degree or above in primary and secondary schools; village affairs open rate; rural gini coefficient; rural governance villager participation rate; income ratio of urban and rural residents; engel coefficient of rural residents; and per capita disposable income of rural residents. An empirical study is carried out with 5 towns (Anzhuang, Wangzhuang, Taoyuan, Wenyang and Sunbo) in Feicheng City, Shandong Province. The weight of each evaluation index for the evaluation of the rural revitalization level of each township is determined based on the analytic hierarchy process and Delphi method. A comprehensive evaluation method is used to establish an evaluation model of rural revitalization level and calculate the rural revival level index of each township. The rural revitalization index of Anzhuang Town, Wangzhuang Town, Taoyuan Town, Wenyang Town and Sunbo Town are 0.850 7, 0.848 8, 0.844 2, 0.811 2, 0.781 0 respectively. Anzhuang Town, Wangzhuang Town, Taoyuan Town, and Wenyang Town have a relatively high level of rural revitalization. The rural revitalization level of Sunbo Town is lower than the above 4 towns and needs to be improved. In the context of the implementation of the rural revitalization strategy, the research on the evaluation indexes and models of rural revitalization level is not only important for scientifically measuring the level of rural revitalization, but also for monitoring and early warning and correcting the level of rural revitalization, and it would play a positive role to promote the implementation of strategy. [ABSTRACT FROM AUTHOR]

Temperature and precipitation extremes are the dominant causes of natural disasters. In this study, seven indices of extreme temperature and precipitation events in Gansu Province, China, were analysed for the period 1961–2017. An abrupt climate shift was recorded during 1980–1981. Thus, the study period was divided into a preshift (before the climate shift) period 1961–1980 and an aftshift (after the climate shift) period 1981–2017. Comparison of mean extreme indices for preshift and aftshift periods was performed for the purpose of exploring possible increasing/decreasing patterns. Generalized extreme value (GEV) distribution was applied spatially to fit the extreme indices with return periods up to 100 years for preshift/aftshift periods. Singular value decomposition (SVD) was adopted to investigate possible correlation between the extreme climate events and indices of large-scale atmospheric circulation. The results indicate that changes in mean and return levels between the preshift and aftshift periods vary significantly in time and space for different extreme indices. Increase in extreme temperature regarding magnitude and frequency for the aftshift period as compared with the preshift period suggests a change to a warmer and more extreme climate during recent years. Changes in precipitation extremes were different in southern and northern parts of Gansu. The precipitation extremes in the north have increased that can result in more serious floods and droughts in the future. SVD analyses revealed a complex pattern of correlation between climate extremes and indices of large-scale atmospheric circulation. Strengthening of westerlies and weakening of the south summer monsoon contribute to the complex changing patterns of precipitation extremes. Results in this study will contribute to disaster risk prevention and better water management in this area. [ABSTRACT FROM AUTHOR]

• Classification of flood events into typhoon and non-typhoon rainstorm floods. • Key parameters in HEC-HMS model were systematically different for the two types of floods. • Impact of land use change on typhoon floods was smaller than that of non-typhoon floods. • Frequency distribution of the mixture flood series with the effect of land use change. There are two major types of rainstorms in the Asia-Pacific region –typhoon induced rainstorm and non-typhoon rainstorm. This study investigated and separated the different flood responses to these two types of rainstorms, based on a scheme that combined the classification of typhoon and non-typhoon rainstorm floods, the simulation from a distributed hydrological model, and a method to forward restore the impact of land use change on flood frequency analysis. For flood events in a typical basin on the southeast coast of China, the flood characteristics in response to typhoon and non-typhoon rainstorms were significantly different in three aspects: (1) The key parameters in the HEC-HMS model were systematically different. The initial loss and wave velocity of the model were apparently larger for the typhoon rainstorm flood than for the non-typhoon rainstorm flood. (2) The impacts of land use change were different, with smaller effect on typhoon induced floods than on non-typhoon floods under the same magnitude of flood peak flow. (3) Classification of two types of floods resulted in more reasonable frequency analysis affected with the land use change because the annual maximum flood series is the mixture of typhoon and non-typhoon rainstorms. Frequency analysis for the forward-restored mixture flood series showed that the land use change with the decrease in the area of forest land and the increase of garden and construction land resulted in the increase of the mean maximum flow from 2266.6 to 2510.19 m3/s, but the values of coefficient of variation were slightly altered, the ratio of skewness coefficient to variation coefficient were unchanged. The results provide new ideas and methods for a deeper understanding of the impact of land use change on flooding in typhoon and non-typhoon co-action regions. [ABSTRACT FROM AUTHOR]

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Flood event consists of peak discharge and flood volume that are mutually correlated and can be described by a copula function. For a given bivariate joint distribution, a choice of design return period will lead to infinite combinations of peak discharge and flood volume. A boundary identification method is developed to define the feasible ranges of flood peak and volume suitable for combination, and two combination methods, i.e., equivalent frequency combination (EFC) method and conditional expectation combination method for estimating unique bivariate flood quantiles are also proposed. Monte Carlo simulation method is used to evaluate the performance of these combination methods. The Geheyan reservoir in China was selected as case study. It is shown that the joint design values estimated by the two proposed combination methods are both within the feasible range, which means that the methods could be selected for designing unique flood quantiles. The proposed bivariate combination methods are also compared with univariate method, and the reservoir water level estimated by EFC method is higher than the other methods, which means the EFC method is safer for reservoir design. The developed approach provides an applicable way for the identification of feasible range and flood quantile estimation. [ABSTRACT FROM AUTHOR]

The Changwu tableland is located in the semi-humid to semi-arid transition area of the Loess Plateau, China. In the present study, the daily potential evapotranspiration (ET0) of the Changwu tableland was calculated using the FAO Penman-Monteith (FPM) equation for the years 1957-2012, and the temporal variation and frequency distribution characteristics were analysed. The results indicate that the annual average ET0 of the Changwu tableland was 949.3 mm, varying from 789.2 to 1093.3 mm; a slight downward trend with a rate of -0.48mm year-1 was found. An abrupt increase occurred in 1994. The ET0 values that correspond to frequencies of 5, 10, 25, 50, 75, 90 and 95% were 1076.8, 1047.6, 999.7, 947.8, 897.3, 853.0 and 827.0 mm, respectively. The recurrence intervals of maximum and minimum ET0 were both more than 50 years. The contributions of Tmax, Tmin, vapour pressure, wind speed and sunshine hours to changes in ET0 were 0.74, 0.07, -0.51, -0.57 and -0.23, respectively. The change in ET0 and the meteorological factors in the Changwu tableland are worthy of attention; measures to reduce the negative impacts of climate change are necessary. [ABSTRACT FROM AUTHOR]

Precipitation extremes could cause a series of social, environmental and ecological problems. This paper, taking Heihe River basin, the second largest inland river basin in China, as the study area, focused on the frequency analysis of precipitation extremes based on the historical daily precipitation records (1960-2010) at nine stations. Generalized Pareto distribution (GPD) was employed for fitting the peaks over threshold (POT) series, in which Hill plot, percentile method and the average annual occurrence number were used to select the threshold in GPD. Maximum likelihood estimate and L-moment were used to estimate the parameters. The inherent assumptions for POT series were investigated by auto-correlation coefficient, Mann-Kendall test, Spearman's ρ test, cumulative deviation test and Worsley likelihood ratio test. 10, 20, 50 and 100 year precipitation extremes for Heihe River basin were calculated and analyzed as well. It was found the POT series derived from several methods involved were approximately independent and stationary, and GPD could give a satisfactory fit to the POT series for each station. For the upper and lower reaches, the frequency of precipitation extremes at long return periods (20, 50 year or longer) presented increasing in recent years, and the intensity of the highest precipitation were getting stronger as well. The intensity of the highest precipitation extremes for the lower reach (21 and 35 %) increased higher than those for the upper reach (10 and 11 %). For the middle reach, the frequency of precipitation extremes (over 20 year return level) was not found to be increased. The uneven spatial and temporal distribution of precipitation extremes for the basin especially for the upper and lower reaches were getting more and more serious, which would bring great challenges for the local water allocation and management. [ABSTRACT FROM AUTHOR]

Chen, Y.; Huang, W., and Xu, S., 2014. Frequency analysis of extreme water levels in east and southeast coasts of China with analysis on effect of sea level rise. Qiantang bore as well as the storm surge are great disasters for river bank protection at the estuary of Qiantang River. Pearl River estuary is also frequently attacked by strong typhoon storm surge. The risk of damage from storm surge is expected to increase in both estuaries, exacerbated by sea level rise (SLR) and possible climate-induced increases in typhoon intensity and frequency. Adequate estimation on extreme water level will be essential to the coastal flood mitigation for both estuary areas with the effect of climate change. In this study, the popular frequency models Weibull, Lognormal, Gumbel, P-III and GEV are compared on Ganpu station located at the estuary of Qiantang River and Denglongshan station in Guangdong province, the optimal GEV model is recommended. For the risky analysis and management concern induced by the shortage of studied data, the estimated 50 year and 100 year extreme water levels respectively at Ganpu and Denglongshan stations are recommended in this study. Both studied stations located at different estuaries are all type II GEV model as the parameter of GEV distribution are higher than 0. The difference of the parameter and the reason causes the difference in the studied stations are analyzed and discussed in this paper. Furthermore, with the estimated 2.9mm/yr SLR by sea level bulletin of China, effect of SLR in frequency analysis on Denglongshan station is discussed. [ABSTRACT FROM AUTHOR]

Zhou, Z.; Liu, S.; Hua H.; Chen, C.S.; Zhong G.; Lin, H., and Huang, C.W., 2014. Frequency analysis for predicting extreme precipitation in Changxing station of Taihu Basin, China. Rainfall induced flooding is one of the most severe natural disasters in coastal regions. In recent years, along with global warming and sea level rising, extreme hydrological events, such as extreme precipitation, are of high occurrence. Meanwhile, rapid urbanization makes the urban environment transformed dramatically and results in additional flood ventures. Taihu Basin, located in Yangtze Delta, is the richest basin in China and flood control planning in this region is of high significance. Therefore, precipitation analysis, as a basic work of flood design, should be accurate and precise. In this study, based on precipitation data at Changxing Station of Taihu Basin, precipitation frequency analysis using mixed methods is performed. Two of the most applied distribution models, Pearson-III (P3) and Generalized Extreme Value (GEV), are investigated. For parameter estimation method of probability distribution functions, maximum likelihood estimation (MLE) and L-moments (LM) are used. In addition, seeking-matrix curve fitting based on conventional moments (CM) is also investigated to compare the calculation results. The performance of mixed methods is tested by two classical goodness-of-fit tests, Chi-Square test and K-S test. Consequently, GEV distribution model based on LM is evaluated to be the best fitting model for identifying and predicting future precipitation occurrence. So precipitation estimations from different return periods at Changxing Station are identified. This study is a new attempt to precipitation frequency analysis in the stations of Taihu Basin and the result can provide a reference for flood risk and water resource management in Taihu Basin and even in more other regions in China. [ABSTRACT FROM AUTHOR]

River runoff is not only a crucial part of the global water cycle, but it is also an important source for hydropower and an essential element of water balance. This study presents a system-theory-based model for river runoff forecasting taking the Hailiutu River as a case study. The forecasting model, designed for the Hailiutu watershed, was calibrated and verified by long-term precipitation observation data and groundwater exploitation data from the study area. Additionally, frequency analysis, taken as an optimization technique, was applied to improve prediction accuracy. Following model optimization, the overall relative prediction errors are below 10%. The system-theory-based prediction model is applicable to river runoff forecasting, and following optimization by frequency analysis, the prediction error is acceptable. [ABSTRACT FROM AUTHOR]

Highlights: [•] Distributions of four runoff quality indicators are derived from continuous simulation. [•] Impacts of runoff control schemes are analyzed from the distributions. [•] Marginal benefits of improving water quality diminish as runoff control level increases. [•] Pre-flood season has higher water quality risk than other seasons after runoff control. [•] Our approach helps frame a risk-based decision making for urban runoff management. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a 91-year data set at the Wusong Station near Shanghai City in Yangtze Estuary has been used to estimate the 100-year Annual Maximum Water Level (AMWL). The performances of four common distribution models have been evaluated. The GEV model provides the best estimates of an AMWL. It results in the minimum difference (0.04m) compared to the observed 92-year AMWL, with the high correlation coefficient (0.99) and minimum root-mean-square-error (0.045m) value. Predictions from other distribution models cause non-negligible deviations, underestimating the 92-year AMWL by 0.57, 0.38, and 0.15m for Weibell, Lognormal, and Gumbel distribution models, respectively. In order to examine the effects of a shorter data set, a 59-year data set was investigated. Model predictions using 59-year data set underestimates the observed 60-year AMWLs. By comparing to the 100-year AMWL estimated by the GEV distribution, using the 91-year data set, results using the shorter 59-year data set lead to underestimates of the 100-year AMWL by 0.78m for Weibull, 0.58m for Lognormal, 0.38m for Gumbel, and 0.39m for GEV distributions. Therefore, one should be cautious when estimating the 100-year AMWL if the data set covers a period much shorter than 100 years. Selecting an appropriate distribution model can improve prediction accuracy. [ABSTRACT FROM AUTHOR]

An economic valuation of flood reductions arising from land use changes induced by the Conversion of Cropland to Forest and Grassland Program (CCFGP) in China is detailed in this paper. A distributed hydrologic model is used to analyze and predict changes in the probability of flood occurrences in the Yellow River Basin (YRB) due to revegetation activities under the CCFGP. The expected value of flood reductions due to the avoided flood damage potential is then estimated. Losses brought about by each type of flood in the YRB over time and the probability change in flood occurrences are used in the calculation. Results show that the economic benefits from flood reductions will total China Yuan 362 million during 2010–2020. The inclusion of this economic benefit into a benefit-cost analysis of the CCFGP provides a more comprehensive assessment of the program. Implications for prioritizing management options to mitigate flood disasters in the YRB are drawn. [ABSTRACT FROM AUTHOR]

Two models are herein presented to derive at-site hourly based rainfall depth-duration-frequency (DDF) relationships by incorporating daily rainfall information. The model development is motivated by the desire to utilize daily rainfall data that are in existence prior to the conversion from a manned gauge to an automatic one for improving the establishment of hourly based rainfall DDF relation at the site. The performance of the proposed models is assessed by comparing the rainfall DDF relationships derived from the conventional method using solely annual maximum rainfalls of various durations. Hourly rainfall data at Hong Kong Observatory over the period of 1884–1990 are used to demonstrate the application of the two proposed models and to examine their performance. Results from the numerical experiments show that the two proposed models, which incorporate daily rainfall data, are capable of producing more accurate and reliable rainfall DDF relationships than the conventional method solely on the basis of annual maximum hourly rainfalls. [ABSTRACT FROM AUTHOR]

Rainfall depth (or intensity) of the same frequency should follow a non-decreasing relationship with rainfall duration. However, due to the use of finite samples and sampling error, rainfall frequency analysis could yield rainfall intensity (depth)–frequency (IDF, DDF) curves of different durations that might intersect among them. Results of this kind violate physical reality and it is more likely to occur when rainfall record length gets shorter. To ensure the compliance of the physical reality, this paper applied the scale-invariant approach, in conjunction with constrained regression analysis, to circumvent intersections in rainfall IDF or DDF curves. Rainfall data of various durations at rain gauge in Hong Kong are used to demonstrate the procedure. Numerical investigation indicates that the proposed procedure yields more reasonable results than those based on the conventional frequency analysis, especially when only a small sample of data are available. [ABSTRACT FROM AUTHOR]

This paper investigates the nonstationarity of precipitation extremes by incorporating time-varying and physical-based explanatory covariates, using daily precipitation data across the Beijing-Tianjin-Hebei (BTH) region, China. We perform the stationary and nonstationary generalized extreme value (GEV) models based on the Bayesian framework to estimate the expected return levels of precipitation extremes with the 90% credible intervals. Results reveal that the nonstationarity of precipitation extremes is not prominently visible for the majority of sites in BTH. However, the nonstationary GEV models exhibit better performance to capture the variations of precipitation extremes by comparison to the stationary models based on four evaluation criteria. Further, this work attempts to determine the best covariate to illustrate the possible effects of environmental changes on the frequency analysis. Results indicate that the El Nino-Southern Oscillation (ENSO) is the top of the best covariates, followed by the East Asian summer monsoon, North Atlantic Oscillation (NAO) and local temperature anomaly. Moreover, the best covariates are dominated by the physical-based covariates, and the best models with nonlinear functions of covariates are found in the majority of sites. Finally, the best-fitted models are used to estimate the design values of return levels in precipitation extremes. Results illustrate that the differences between the stationary modeling and nonstationary modeling in the median condition of covariates are not significant for most of the sites. But the discrepancies will be enhanced if the covariates locate in a high (95-percentile) or low (5-percentile) value. Our findings suggest that the nonstationary modeling of precipitation extremes might prove more useful and reliable, especially in the uncommon conditions of physical-based covariates. Unlabelled Image • Nonstationary frequency analysis can better capture the temporal evolution of precipitation extremes • The best covariates for nonstationary modeling of precipitation extremes are dominated by the physical-based covariates • Higher return period indicates higher uncertainty in expected return levels both for stationary and nonstationary models [ABSTRACT FROM AUTHOR]

• The GEV, P-III, LN2 and LN3 performed better in China. • The return periods increased as the EPIs increased. • The increases in most EPIs were significant especially in northwest China. • The RX5day and CWD decreased in western China. • The CDD decreased in almost the whole of China. The cumulative distribution functions (CDFs) of extreme precipitation indices (EPIs) characterize the occurrence of extreme precipitation events, but some CDFs have been either exaggerated or underestimated. In this study, we selected the most suitable CDFs from ten commonly used functions (i.e., Normal, two- and three-parameter log-normal, extreme value type-I, generalized extreme value-GEV, Weibull, two-parameter Gamma, Pearson-III type, Poisson, and Pareto) for the site- and regional-specific EPIs in China and projected their changes under the Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios combined with 28 general circulation models (GCMs) in Coupled Model Inter-comparison Project phase 5. Using the most appropriate site-specific CDFs, the spatial and temporal variations of the nine EPIs for the historical and projected future periods at 10-, 20-, 50- and 100-year return periods were investigated. The results showed that the GEV, Pearson-III, three- and two-parameter log-normal were generally the best CDFs for the 9 EPIs in China. By comparing the results during 2021–2100 with 1961–2017, the return periods increased as the EPIs increased. It was especially apparent in southeast China where the annual mean precipitation was above 1300 mm. The increases of the trends were significant for EPIs (especially in northwestern China), including the maximum 1 day precipitation, number of heavy precipitation days, number of very heavy precipitation days, extremely wet days and annual total wet day precipitation. The simple daily intensity index increased in northeast China, decreased in western China, but had no significant change in other regions. The maximum 5-day precipitation and consecutive wet days decreased in most areas except western China. The consecutive dry days decreased in northern China and increased in southeast China. This study provides region- and site-specific optimal CDFs and return period information and reveals the spatiotemporal changes of 9 EPIs at different return periods of 10-, 20-, 50- and 100-years under the RCP 4.5 and RCP 8.5 scenarios for 2021–2100. The obtained results are useful for guiding disaster-prevention efforts in different regions of China. [ABSTRACT FROM AUTHOR]

The stationarity of observed hydrological series has been broken or destroyed in many areas worldwide due to changing environments, causing hydrologic designs under stationarity assumption to be questioned and placing designed projects under threat. This paper proposed a data expansion approach-namely, the cross-reconstruction (CR) method-for frequency analysis for a step-changed runoff series combined with the empirical mode decomposition (EMD) method. The purpose is to expand the small data on each step to meet the requirements of data capacity for frequency analysis and to provide more reliable statistics within a stepped runoff series. Taking runoff records at three gauges in western China as examples, the results showed that the cross-reconstruction method has the advantage of data expansion of the small sample runoff data, and the expanded runoff data at steps can meet the data capacity requirements for frequency analysis. In addition, the comparison of the expanded and measured data at steps indicated that the expanded data can demonstrate the statistics closer to the potential data population, rather than just reflecting the measured data. Therefore, it is considered that the CR method ought to be available in frequency analysis for step-changed records, can be used as a tool to construct the hydrological probability distribution under different levels of changing environments (at different steps) through data expansion, and can further assist policy-making in water resources management in the future.

Shanghai, as a coastal city, is vulnerable to various types of flooding. The floodwalls along the Huangpu River provide protection against typhoon-induced flooding. However, there is limited insight into the actual safety level of the flood defences in Shanghai, and recent failures have highlighted their vulnerability. Therefore, the aims of this paper are to derive a series of new flood frequency curves for the Huangpu River, and to evaluate the level of protection of the floodwall system. This paper analysed over 100 years (1912–2013) of annual maximum water levels for three stations at near-sea, mid-stream and inland locations along the Huangpu River. Best-fit curves were determined for a number of selected probability distributions using statistical performance indicators. As a result, new flood frequency curves of the water levels for different storm surge return periods were produced. The results showed that generalised extreme value (GEV) was identified as the most suitable probability distribution for the datasets. Analysis showed that the current design water levels correspond to exceedance probabilities of 1/500 per year at the near-sea and mid-stream stations, and no more than 1/50 per year at the inland station of the Huangpu River, whereas the intended safety standard is 1/1000 per year. A comparison of the findings with a dataset of the crest heights of the floodwalls showed that the current protection level of the floodwalls along the Huangpu River is expected to be around 1/50 per year in terms of overtopping for the lowest sections. The results of this study can be utilized to provide future recommendations for flood risk management in Shanghai. [ABSTRACT FROM AUTHOR]