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In order to find out the variation law of total dissolved solids (TDS) in groundwater in different buried depth areas, this paper took the People’s Victory Canal Irrigation Area as the research area, and divided into high value area, transition area and low value area according to TDS value, the optimal Copula function was selected by AIC criterion, the optimal Copula function was used to build the joint distribution between groundwater depth and TDS in different regions and analyze the relationship between the two. The results show that there is a strong positive correlation between groundwater depth and TDS in different regions, the optimal edge distribution of groundwater depth and TDS in the high value area is Gamma distribution, the optimal edge distribution of groundwater depth in transition area and low value area is Weibull distribution, and the optimal edge distribution of TDS is Gamma distribution. The optimal joint distribution function of the burial depth of each typical observation well and TDS is the Frank Copula function. According to the joint probability contour, when the groundwater depth and TDS increase, the joint probability value also increases; When the joint probability value is constant, TDS decreases with the increase of groundwater depth and tends to be stable; The joint probability contour can also reflect the probability of TDS under any groundwater depth, and the possible combination between different groundwater depths and TDS under the same probability. [ABSTRACT FROM AUTHOR]

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The frequent occurrence of drought events in the irrigation district has seriously restricted the sustainable and green development of agriculture. In order to quantitatively analyze the drought risk in the Renmin Shengli Canal irrigation area, this paper built the standardized precipitation evapotranspiration index (SPEI) at different time scales based on monthly precipitation and average temperature data of the irrigation district from 1951 to 2017. It identified two characteristic variables of drought duration and drought intensity by the run?length theory in different time scales, and established a joint probability distribution function to analyze the joint distribution probability and co?occurrence return period of drought at different time scales in the irrigation district. The results show that the fluctuation of SPEI value decreases with the increasing of time scale; the maximum drought duration and drought intensity under different time scales are different, and the drought intensity of SPEI12 is the highest(24.4) when the drought duration is 31 months; the drought events of SPEI1, SPEI3 and SPEI6 in the irrigation district are mainly short duration and low intensity, while SPEI12 has less long duration and high intensity. The drought joint distribution probability and co?recurrence periods in different time scales are different, for example, in the SPEI6 scale, the joint distribution probability is 19.65% and the rate of change of the joint distribution probability is 32.37%, when the drought duration is more than 5 months and drought severity is greater than 5, and the co?recurrence period is 1.65 a when the drought duration is 5 months and drought severity is 5. [ABSTRACT FROM AUTHOR]

Under the influence of climate change and human activities, the analysis of the Hydrological situation during ice flood period is of great significance to the study of prevention and mitigation of ice flood disaster. In this paper, the peak break-up discharge of Sanhuhekou Hydrological Station in Ning-Meng reach of the Yellow River was selected as the research object, its effect variables（the peak break-up water level and average ice thickness） were obtained through correlation analysis. Mann-Kendall and Pettitt tests were used for change-point tests of univariate variables, on the basis of these results, Copula-based likelihood ratio test（CLR） method was used for change-point detection of the multivariate series. The results show that for univariate series, there is no significant mutation for the peak break-up discharge, the peak break-up water level mutates in 1968 and average ice thickness mutates in 1987. For Pair-Copula structure, the tree 1 does not change significantly, while the tree 2 mutates in 1996. After comparison, it finds out that the correlation between variables before and after the change-point is significantly different. The possible reason for the mutation is that the continuous silting of the channel which leads to the keep rising of water level during the freeze-up period and the break-up period. [ABSTRACT FROM AUTHOR]

Based on Copula function and Markov process, the two-dimensional random simulation model of water supply and demand time series in irrigation area was built by this paper. Taking Luhun irrigation area in Henan Province which is a typical canal irrigation area in northern China as an example, the annual precipitation and reference evapotranspiration from 1970 to 2013 were used as base data-structure in this study. Applying this simulation model, 500 years of simulated data was generated for Luhun irrigation area. The results show that this model can reflect the statistical properties of the original series; at the mean time it meets the temporal dependence of time series of two variables themselves, 〖JP2〗as well as the spatial structure dependence between two variables. And the result of the random simulation has been proved feasible. [ABSTRACT FROM AUTHOR]