Abstract: Taking summer maize in Henan province as an example, based on observed crop data during growing period from 1981 to 2010, yield data from 1961 to 2010, and daily meteorological data from 9 representative stations, 6 different types of continuous overcast and rainy days were designed. The relationship between yield reduction rate and overcast days during mid and late growth period of summer maize was analyzed by extracting yields reducing rate serials, selecting continuous rain days in lean years. The multiple linear regression equation for the effect of disaster on yield reduction was established, by comparing the high frequency overcast and rainy days and average value, the meteorological disaster index of continuous rain during flowering phase and grain filling phase for summer maize was determined respectively, and the possible yield loss rate was estimated. The results showed that, within the different grades of yield reduction rates, there was positive correlation between all kinds of continuous rain days and yield reduction rate 5%-20%, of which, the index of continuous lack of sunlight had high correlation with yield reduction rate between 5%-10%, while the index of continuous rain days had high correlation with yield reduction rate 15%-20%. Continuous rain or lack of sunlight at flowering stage had high correlation with yield reduction rate at grain filling stage. Meteorological disaster index of continuous rain was expressed by longest consecutive days without sunshine (N1), longest consecutive days of sunshine time less than 2 hours (N3), longest consecutive rain days (P1), longest combination days that consecutive rain and sunshine time less than 2 hours in rain free days (P3). The index was divided into two grades of light and heavy, and the average yield reduction rate under light disaster was 10.4% and 8.5% at flowering and grain filling stage respectively. The results could provide basic evidence for meteorological support service on high and stable yield of summer maize.

Key words: Summer maize, Flowering stage, Grain filling stage, Days of continuous rain, Meteorological index