Indicator-based spatiotemporal characteristics of apple drought in North China

Frequent occurrences of drought stress caused by dry weather create severe destroy in apple yield and quality in North China. Although appropriate drought stress is beneficial to apple planting, it might change to apple drought disaster when dry weather continues and reaches to a certain magnitude. So, precisely identification of apple drought based on weather condition is of great merit to provide a basis for targeted apple drought monitoring, early warning and evaluation. To explore the trigger dry weather condition of an apple drought event, apple drought index (ADI) was firstly constructed by the consideration of physiological water demand and precipitation characteristics. The ADIs in historical apple drought disaster samples were reanalysed in North China, and the distribution-type fitting and confidence interval method were used to identify the drought trigger thresholds in the apple drought indicators. Afterwards, spatiotemporal characteristics of apple drought in North China during 1981 to 2018 were explored based on the apple drought indicators. Drought trigger thresholds were ADI 0.86, 0.84 and 0.76 for apple tree germinating to bud brush (P1), bud brush to flowering (P2) and flowering to maturity (P3), respectively. 81.82% of drought indicator-based results were strongly consistent with historical records about apple drought disasters. Indicator-based regional average apple drought ratios in North China from 1981 to 2018 were 28.27%, 28.33% and 20.82% in P1, P2 and P3, respectively. 2009, 2000 and 2001 were detected the highest drought frequency years for P1, P2 and P3, with drought ratio 57.07%, 60.00% and 40.98%, respectively. The results can provide technical and theoretical support for targeted apple drought detection, and information and measures for apple drought prevention and mitigation can be implemented according to the indicator-based results.