Precipitation in May had 4 wave periods of about 4-year,about 8-year,about 16-year and about 32-year. Wave periods of about 8-year, about 16-year and about 32-year were more notable.

• 5月份降水量有4年左右、8年左右、16年左右和32年左右4个时间尺度的振荡周期,以8年左右、16年左右和32年左右的周期性振荡最强。