Analysis of drought identification and spatio-temporal characteristics for summer corn in Huang-Huai-Hai Plain in year of 1961－2015

In the context of global warming, the frequency and severity of drought are increasing rapidly, and the impact of drought on China's agricultural production is also the largest. In this study, meteorological data of 46 stations, the phenophases of summer corn at 33 agro-meteorological stations and historical disaster data in 1961-2015 in the Huang-huai-hai Plain were integrated to establish crop drought identification indices for summer corn drought disasters. Referring to the calculation formula of standardized precipitation index (SPI), daily SPI10 on the ten-scale and SPI30 on the monthly scale were calculated based on SPI. The SPI10 and SPI30 for summer corn at different developmental stages were formed by establishing the drought sample sequences. The historical disaster data were used to determine the thresholds of SPI10 and SPI30 for different development stages of summer corn. The thresholds were determined basing on a Lilliefors goodness-of-fit test and the upper threshold of a 95% confidence interval. And then the SPI10 and SPI30 for summer corn at sowing-tasseling stage and tasseling-maturity stage in the Huang-huai-hai Plain were constructed and evaluated the fitness by random drought samples reserved independently and other historical drought records. The better indicator and threshold for summer corn drought were selected. On this basis, we analyzed the drought disaster and revealed the spatio-temporal characteristics of drought disaster at different development stages of summer corn, in order to provide basic data for drought monitoring in China. Main results were showed as below: 1) The thresholds of SPI10 for summer corn at sowing-tasseling stage and tasseling-maturity stage were -0.10 and -0.35, respectively. The thresholds of SPI30 for summer corn at sowing-tasseling stage and tasseling-maturity stage were -0.60 and -0.65, respectively. The results identified by SPI10 and SPI30 were basically consistent with the random drought samples reserved independently and historical drought records, and the effect of SPI10 was better. 2) The temporal characteristics of drought for summer corn in the Huang-huai-hai Plain from 1961-2015 were analyzed based on SPI10. The results showed that: The average drought frequency and average drought severity of summer corn at sowing-tasseling stage were significantly higher than that at tasseling-mature period. The time fluctuation characteristics of drought severity in both development stages were consistent with the drought frequency. 3) The spatial distribution characteristics of drought for summer corn in the Huang-huai-hai Plain were analyzed based on SPI10. The results showed that: The interannual variation of the drought extent at sowing-tasseling stage showed an overall increase, but the change trend was not significant. The overall characteristics of the interannual variation of the drought extent at tasseling-maturity stage were not obvious. Drought extent at sowing-tasseling stage was greater than that at tasseling-maturity stage in 75% of the years. Drought frequency at sowing-tasseling stage for summer corn was higher in the southeastern part of the Huang-huai-hai Plain and lower in the central. Drought frequency at tasseling-maturity stage for summer corn was higher in the northwest and south part of the Huang-huai-hai Plain and lower in the southeast. The spatial distribution characteristics of drought severity were consistent with the drought frequency. Generally, the area with higher drought frequency had stronger cumulative drought severity. Moreover, the drought frequency and drought severity at sowing-tasseling stage were higher than that at tasseling-maturity stage. The difference in drought frequency or drought severity was the greatest in the southeastern region of the Huang-huai-hai Plain at both developmental stages.