According to 52-year precipitation data from 20 meteorological stations in Ningxia Hui Autonomous Region from their establishments in 2012

the mathematical analysis methods such as the trend line method and 5-year moving average method were applied to analyze the precipitation variation characteristics in more than 50 years

and the precipitation Z index and the precipitation anomaly indicators of plus or minus 20% points were also used to analyze the characteristics of droughts and floods in the region

then a trend judgment of the droughts and floods was made based on the symmetry of information forecast theory and commensurable calculation method. The results showed:(1) The precipitation in more than 50 years of Ningxia region was reduced at a rate of 8.57 mm/10 a

and the arid trend was obvious since 1990s;(2) The drought and flood disasters occurred alternately

the frequency of drought and flood was 32.7% and 28.7%

respectively

and it was only 38.5% in a normal year;(3) The droughts and floods occured with obvious characteristics of symmetry cycle

the drought years may occur in 2014 and 2015

floods may occur in 2017.