Presentations 2016

Trends in extreme droughts and their impact on grain yield in China over the past 50 years

Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences

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Climate change and climate extremes and their impacts on agriculture, water resources, and ecosystems have become hot issues globally. Agricultural sustainability and food security are facing unprecedented challenges due to the increasing occurrence of extreme climatic events, including notably, extreme droughts in recent years in China. In this study, an agricultural drought index was developed by combining meteorological and crop planting pattern data in different regions and water demand data in different growing seasons. An inverse probability distribution function was derived based on the relationship between CDWEP (consecutive days without effective precipitation, the agricultural drought index) and their corresponding occurrence frequencies. Furthermore, a threshold model of extreme droughts of China was developed. Based on that model, changes in the frequencies and intensities of the extreme droughts in China and their corresponding relationships with the climatic grain yields in rain-fed regions were analyzed over the past 50 years. The whole China was divided into six regions, i. e. Northeast China, North China, Southeast China, Southwest China, Northwest China and Qinghai-Tibet Plateau. The results were as follows: (1) The threshold value of the extreme droughts increased gradually from the southeast to the northwest; the highest value was located in the deserts in the northwest arid areas where the CDWEP was more than 60 days, while the lowest value was in the middle reaches of the Yangzi River, where the CDWEP was less than 16 days; the value in North China was between 20-40 days, while Southeast China had a value of less than 20 days. (2) The frequencies and intensities of the extreme droughts increased in most regions of China except in Northwest China and Qinghai-Xizang Plateau. Stations in North China and in Southwest China showed the two strongest positive trends; the relative change rates in frequency and intensity per station were, respectively, 11.3% and 2.2% for North China, and 9.3% and 2.7% for Southwest China; for Southeast China, the relative change rates in frequency and intensity per station were, respectively, 7.1% and 1.8%; and for Northeast China, that of 5.7% and 0.7%, respectively. (3) A case study in Yushe in North China, Bijie in Southwest China and Meixian in Southeast China indicated that the per unit area climatic grain yields of the rain-fed region had an anti-phase relationship with the frequencies and intensities of extreme droughts. (4) A case study in Shijiazhuang of North China showed that the groundwater depth was on a significant downward trend, with an annual mean change rate of 0.82 m since the 1970s, which was mainly attributed to water exploitation mostly due to agricultural irrigation. After removing the impacts of the exploitation trend on groundwater depth variation, the results indicated that the natural groundwater level depth variation had a positive phase relationship with the annual precipitation and the annual frequencies and intensities of the extreme precipitations but had no evident relationship with the annual frequencies and intensities of the extreme droughts.