Drought evolution of different land cover regions in North China
华北不同地表覆盖类型区干旱演变特征

Ten-day precipitation datasets of the meteorological observation stations in the study area from 1960 to 2008 were used to calculate multi-scale(1 month,3 months and 12 months) Standardized Precipitation Index(SPI) sequences.The long-time scale evolution cycle and extent of the drought in the study area and three kinds of major land type area,i.e.,grassland,cropland and broad-leaved forest land are analyzed by applying moving average and moving standard deviation to SPI historical sequence.The variation and tendency of drought throughout the historical period were analyzed using linear regression method and the trend of line was forecasted.The characteristic differences of the tendency of drought for the three sub-regions were compared in 12 months.The result showed that the intensity and frequency of drought had a gradually serious trend and each month had a greater difference in tendency of drought.June and July had more precipitation than the historical period and the trends of drought in spring(April) and autumn(September and October) are more obvious.During the entire historical period,changing trend of drought in the grassland area is not as obvious as that in cropland of the southern study area and broad-leaved forest land of the central study area.The drought tendency of cropland is obvious in September and October.Summer corn in Huang-Huai-Hai Plain are faced with the threat of more and more autumn droughts,and the situation of droughts is more serious than that of the spring drought posing to winter wheat.The drought will exert greater impact on the autumn sowing for winter wheat.