Analysis And Research On Synchronous-asynchronous Encounter Probability In The Middle Route Of South-to-north Water Transfer Project

The middle route of south-to-north water transfer project plays an important role in dealing with the water shortage problems of Beijing, Tianjin and North China. Involving a long route and several basins, the encounter probability characters of rainfall in different hydrological zones have direct impact on the transfer benefit of the middle route project. It is of great significance to study the encounter probability character of water resource and receiving areas of the middle route of south-to-north water transfer project.The multivariate joint probability distribution method can determine the encounter probability. This paper studies many kinds of multivariate joint probability distribution methods, including the statistical, Copula, TAN, FGM and FEI methods. Adaptability and limits of the above methods are also analyzed and compared with each other.The statistical and Copula methods are applied to analysing encounter probability of rainfall in the middle route of south-to-north water transfer project .The encounter probabilities of water resource and four receiving areas with time scales of year, season, flood season and non-flood season are calculated.The Copula method possesses strong adaptability and flexibility since it can flexibly build the multivariate joint probability distribution with arbitrary marginal distributions. The Copula method is used to calculate the encounter probability of rainfall in the middle route of south-to-north water transfer project and the results are compared with the ones derived with the statistical method. The results of the two methods are close, with a discrepancy of 0.1%-6%. The joint probability distribution model built by the Copula method shows advantages in calculating continuous probability, and the isograms of joint probability distribution probability can be obtained by the Copula method to provide decision support. The Copula method is practically better in hydrologic frequency analysis of multivariate variables.Results indicate that the probabilities of advantage in water transfer increase from south to north. The continuous low water of the water resource area is the worst risk factor which affects the benefit of water transfer. The asynchronous probabilities between receiving areas average about 52.97%. This information is useful for timely water supply in phase. The asynchronous probabilities between receiving areas is the largest in flood season, which suggests that the favorable opportunity in timely water supply for different receiving areas is in flood season.