Evolution of drought and flood trend in the growth period of spring maize in Northeast China in the past 60 years

The evolution of regional drought and flood trend provides a theoretical basis for understanding crop response to climate change, decision making on disaster prevention and reduction, and ensuring China's food security. Here, the northeast region of China was used as the research area, which was divided into 14 parts based on the growth characteristics of spring maize. The daily meteorological data from 78 stations in the study area from 1958 to 2017 were used to calculate the crop water surplus deficit index (CWSDI') of spring maize during the growing period. The CWSDI' values were divided into eight drought and flood levels. The results revealed the temporal and spatial trend of drought and flood during the growth period of spring maize in the northeast region using Mann-Kendall trend test, mutation test, and geographic information system spatial analysis technology. During the growth period of spring maize, CWSDI' generally increased in the three growth stages of sowing-heading period and decreased in the heading-maturation stage, and the decreasing trend was the most significant in the milk-maturation stage, but without any obvious regional difference. The frequency of drought in the growth period of spring maize in the research area was considerably higher than that of flood. The drought situation had gradually worsened since the 1990s, but the flood situation showed no obvious change. The jointing-heading and milk-maturation stages were the least and most affected stages by drought and flood, respectively. The frequency of drought and flood in each growth stage of spring maize was as follows:extreme drought > light drought > other drought and flood levels. The frequency of moderate drought and heavy drought in the western part of Liaoning was higher than that in other areas. Extreme drought mostly occurred in the western part of the study site, whereas light flood mostly occurred in Heilongjiang. Moderate flood and heavy flood rarely occurred in the study site. In the future, efforts should be made to prevent drought and flood in the early and late growth stages of spring maize. Furthermore, more attention should be paid to the western part of the study site owing to the more severe drought situation in order to achieve timely and effective irrigation. The results will provide a basis for the prediction of agricultural drought and flood disasters and optimization of water resource allocation on a regional scale.