Characteristics of agriculture drought in China during 1950-2006

Drought is one of most destructive and recurrent nature disasters. It affects the terrestrial ecosystem (especially agriculture), human activities, and even industries. Drought recurs over many places globally. China has experienced frequent severe droughts during second half of 20th century. Droughts can be classified according to their characteristics and impacts as falling in one of four categories: agricultural, meteorological, hydrological, and socioeconomic. The deficiency of soil moisture is usually used as the index to describe the agriculture drought. Due to the measurement difficulties, land surface/ hydrological models are helpful to produce the long-term soil moisture data sets. Because of the tremendous disparities among models, single model products may not be accurate to represent the variations of soil moisture. In this study, to assess the characteristics of agriculture droughts, monthly values of total column soil moisture from the simulations of four physically based land surface models were used to reconstruct the agricultural drought over China during 1950-2006. An ensemble method was applied to combine all models simulations into a multimodel ensemble from which agricultural drought severities and durations were estimated. Advanced analysis methods including: cluster analysis method and severity-area-duration (SAD) algorithm, and Mann-Kendall trend algorithm were applied to the ensemble soil moisture data to characterize drought spatial and temporal variability. Results show that the major drought events can be identified. For drought areas greater than 150,000 km2 and durations longer than three months, a total of 73 droughts were identified during the 1950-2006 period. The five droughts that were most prominent in terms of severity and spatial extent were during1997-2003, 1975-1981, 1964-197, 1981-1985, and 2004-2006. Each of them spreads over the different regions in China. We also found that soil moisture in north central and northeastern China had significant downtrends, whereas most of Xinjiang, the Tibetan Plateau, and small areas of Yunnan province had significant uptrends. Regions with downtrends were larger than those with uptrends (37% versus 22 % of the land areas), implying that over the period of analysis, the country has become slightly drier in terms of soil moisture. Trends in drought severity, duration, and frequency suggest that soil moisture droughts have become more severe, prolonged, and frequent during the past 57 years, especially for northeastern and central China, suggesting an increasing susceptibility to agricultural drought.