Characteristics of droughts in eastern Northwest China over the past 546 years

Based on the drought/flood grade data for 17 stations during 1470−2008 and precipitation from May to September during 1958−2015 in eastern Northwest China, the sequence of drought/flood grade during the period of 1470−2015 has been established. Spatial and temporal characteristics of the drought variation are analyzed; extreme drought events occurred during the 546 years and the characteristics of drought persistence are discussed in detail. The results show that the drought/flood grade data can well reflect the spatial and temporal characteristics of drought changes over eastern Northwest China. On the century scale, drought occurred most frequently in the 20th century, and the areas of high occurrence frequency are found in Ningxia and Northern Shaanxi. Drought scale factors indicated that the drought persistence in eastern Ningxia and northern Shaanxi was relatively long. Those drought events that covered a large area with high intensity play an important role in the persistence of drought. The drought persistence was significant during periods of 1470−1500 and 1910−1940, when two "one-hundred-year" and even "two-hundred-year" extreme drought events occurred over eastern Northwest China.