Based on the daily precipitation data at 18 meteorological stations of Hainan Island from 1969 to 2018, the spatio-temporal change characteristics of precipitation randomness were analyzed by using information entropy method, Mann-Kendall trend test and spatial interpolation technique of inverse distance weight. The results show that the uneveness of monthly apportionment of annual precipitation and precipitation days increased from east to west of Hainan Island. In recent 50 years, the monthly apportionment unevenness of annual precipitation and precipitation days showed an increasing trend in northern and western areas and part areas of southern Hainan Island, while it showed a decreasing trend in the rest areas on the whole. The spatial distribution of randomness of daily precipitation was significantly different in the whole year and four seasons in Hainan Island, and they were significantly and positively correlated with the proportion of rainstorm and above rainfall days. In terms of time, the randomness of daily precipitation in the whole year and four seasons increased in most cities (counties) of Hainan Island from 1969 to 2018, especially the probability of strong precipitation increased in four seasons. The rainstorms to torrential rains in central, northwestern, eastern and eastern Hainan Island should be paid enough attention in spring, summer, autumn and winter, respectively.

Based on the daily precipitation data and agricultural flood disaster data in Hainan Island from 1966 to 2015, the grey relation analysis method and correlation analysis method were used to revise the monitoring indicator of agricultural flood disaster. The agricultural flood disaster monitoring indicator was gradually selected by combining with historical flood records and agricultural areas suffering from agricultural flood disaster, the temporal and spatial distribution features of agricultural flood disaster were analyzed in the area for nearly 50 years using this indicator. The results are as follows:(1) The agricultural flood monitoring indicator was the initial indicator threshold plus 22 mm in Hainan Island. The agricultural flood index which was calculated by revised indicator had significant correlation with the agricultural flood-affected ratio, the inundated rate and the barren rate, and the correlation coefficients were 0.36 (P<0.05), 0.53 (P<0.01) and 0.40 (P<0.05), respectively. (2) The frequency of large agricultural flood increased relatively in the rest of the time in Hainan Island except the 1980s in which it decreased obviously. Meanwhile, the agricultural flood areas concentrated on the central and eastern regions and gradually expanded from the central and eastern regions to the northern and western regions.