Impact of climate warming on drought characteristics of summer maize in North China Plain for 1961–2010
North China Plain (NCP) is the major grain production region of the rain-fed summer maize and its natural climatic conditions play a decisive role in maize growth process. In this study, we focused on temporal-spatial characteristics of drought during maize growth period (June-September), and wanted to access the impact of climatic warming trend on summer maize drought during its growing season in NCP. To understand these questions, we used monthly mean air temperature and monthly precipitation data of 27 stations in NCP from 1961-2010. First, jumping points of mean temperature and precipitation in maize growth period were fixed by Mann-Kendall test method. Second, the self-calibrating Palmer Drought Severity Index (SC-PDSI) was used to calculate the drought level and the drought distribution characters were captured by empirical orthogonal function (EOF). Third, analyses of drought occurrence probability were conducted under two scenarios, i.e. one was actual observations, and another consisted of monthly actual precipitation for each year and past 50 years average of monthly mean temperature. Results showed that mean temperature and total precipitation in maize growth period were in a slightly decreasing trend before 1996, which was the jumping time point of mean temperature. After 1996, mean temperature of maize growth period was higher than the 50 years average of 0.4°C-1.0°C, while the trend of total precipitation in maize growth period was transferred from decreasing to increasing. The spatial character of drought occurrence in maize growth period showed consistency in NCP, and the most prone to drought and the hardest drought area was located in Henan Province. Drought occurrence probability increased by an average of 10.1% due to climate warming appeared since mid-1990s, and above severe drought increased in an average of 9% at the same time. These increase extent were higher than that of the decreased ones before the mid-1990s when temperature was lower than 50 years average. In addition, the proportion of above severe drought occurrence also rose with the climate warming. Therefore, the warming trend would have a significant effect on drought occurrence of summer maize in NCP.