The changes in drought and flood during the 12 years from July to September can be seen,. They
included nine normal years, a severely dry year in 2006, a severely wet year in 2007, and an extremely
wet year in 2010.Since 2006, the frequencies of drought and flood have tended to be higher, and the
frequency of flooding is higher than that of drought. When we take the total precipitation of the three
months as the factor for calculating the Z index, the change in the drought and flood situation is not
obvious, perhaps due to the offsetting effect of the three month period. But, from an overall point of
view, it tells us the precipitation situation in the whole summer, which is the main growth season of
crops