Crop Drought Identification Index for winter wheat based on evapotranspiration in the Huang-Huai-Hai Plain, China

摘要

Frequent occurrences of drought events can lead to winter wheat drought disasters. To prevent drought damage and reduce potential losses, it is important to establish an index to provide support for winter wheat drought monitoring, prevention, and mitigation, and further to understand the precise spatiotemporal characteristics of winter wheat droughts. In this study, meteorological factors, remote sensing products, disaster records, and phenophases of winter wheat in the Huang-Huai-Hai Plain were integrated to establish a Crop Drought Identification Index for winter wheat drought disasters. The CDII was expressed as the ratio of actual evapotranspiration (ETa) and crop evapotranspiration under standard conditions (ELc), in which ETa was simulated through the Two Source Energy Balance (TSEB) model and ETc was calculated based on the Penman-Monteith method using daily meteorological data and MODIS remotely sensed products. The CDII for winter wheat at different developmental stages was formed by establishing the drought sample sequences and determining the thresholds based on a Lilliefors goodness-of-fit test and the upper threshold of a 95% confidence interval. Validation showed that the identification results by CDII corresponded with 86.2% drought records. The spatial distributions of drought characteristics for winter wheat in the Huang-Huai-Hai Plain were mapped. The thresholds of the CDII at the before wintering stage, returning green-jointing stage, and heading stage were higher than that at the other two developmental stages. Drought frequency was higher across the whole Huang Huai-Hai Plain at the before wintering stage and returning green-jointing stage of winter wheat. The regions with higher drought frequency were concentrated in the northern part of the Huang-Huai-Hai Plain at the heading stage and in the mid-western Shandong Province at the milky ripening physiological maturity stage. This study took the drought distribution in the 2006-2007 growing season and heading stages from 2000 to 2013 as examples, the results indicated that the CDII could identify the actual drought of winter wheat reasonably. The findings indicate the CDII is useful for monitoring and assessing winter wheat drought disasters at a regional scale. It can also provide a new method for crop drought analysis.