Research on the correlation of drought/flood spatial fields by using joint entropy

Using a method of calculating the entropy based on the relativity of spatial fields to give a correlative index having the statistic characteristic of discrete spatial fields, we discuss the inherent rule. of drought/flood and their spatial distributions in China. The result gives the associations of drought/flood distributions from 1470 to 2000, and shows that the actual relativity of drought/flood distributed fields is relative and not stochastic, being different from the random distributed fields, by calculating their entropy and matrix latent values. The every year's entropy shows the degree of the year's association with other ones. The greater the entropy is, the bigger the degree is, and vice versa. The similitude of climate state has a steady and obvious quasi-periodicity before 1820, whose size is about 113 years. After 1820, the size adds up to 130 years and the intensity is weakened. Another steady quasi-periodicity is 68 years, which is obvious from 1595 to 1820, and its size is changed from 61 years to 81 years. In other periods, the 68-year periodicity is not found obviously.