| Drought is one of the most common and deepest influential natural disasters in the Circum-Bohai-Sea region, it has significant scientific and practical value to alleviate drought damage and develop agricultural production by the study of its variation and characteristics. Based on the monthly temperature and precipitation data of 52 meteorological stations from 1961 to 2014, which were homogenized, and referenced historical data of drought events in the past, we used the statistics analysis, Mann-Kendall test, precipitation anomaly percentage, Z index and SPEI index, IDW spatial interpolation methods by R, ArcGIS, DPS, SPSS software, and analyzed the characteristics of climatic variation in the study area as well as the applicability of the three kinds of drought indices. Finally, we discussed the driving factors of seasonal droughts, such as ENSO events, sunspots, the East Asia summer monsoon and the Pacific decadal oscillation and southern oscillation. The results show that:?1? The mean annual temperature of the Circum-Bohai-Sea region was experienced fluctuation growth trend with a speed of 0.30?·10a-1, the annual precipitation was experienced fluctuation with “W” trend at 10.48mm·10a-1. Overall, climate change was a warming and drying trend. Among them, especially in Beijing-Tianjin-Hebei region, the temperature's rising rate and precipitation's decreasing rate were the fastest. Summer precipitation reducing was the most significant, spring and winter warming trend were most obvious.?2? Three kinds of drought indices showed large differentiation in degree, frequency and space temporally. Pa and Z index were similar in fluctuation trend, but drought event by Pa index indicated often lagged and be less, Z index was not characterized. However, the characteristics of drought by SPEI index indicated were consistent with the data recorded, so it was an optimal index of drought in this area.?3? The SPEI-12 index declined significantly, and the spatial extent of drought increased gradually. Especially the period of the 1980 s and the first five years of the 21st century were frequent and severe. There were 11 years of domain drought, 8 years of regional drought, 2 years of partial-local drought, 18 years of local drought, and 16 years of no obvious drought. The spatial distribution of drought showed heterogeneity. The high frequency of annual drought focused on Beijing, west and south of Liaoning province, and some areas of Shandong province also distributed dispersedly. Spring drought mainly concentrated in Shandong Province, which was almost domain drought, and summer drought concentrated in the central and western part of the Bohai Sea, which formed two Northwest-southeast irregular arid zones, autumn drought concentrated in the western of Liaoning Province, winter drought formed a North-South small arid zone in the east of Shandong Province.?4? Seasonal droughts were affected by various factors. El Nino was one of the main factors, which reduced the precipitation and strengthened the possible of drought. Sunspots mainly affected the autumn precipitation, whose acuteness activity might reduce the autumn rainfall. The Southern Oscillation Index and ENSO events affected drought on the contrary, the active Oscillation could increase the precipitation. Other influencing factors were not the main factor. |
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