| Drought is natural disasters on earth which has broader space, longer duration and the worst socioeconomic and environmental impacts. Economic losses caused by drought accounted for 50% of all natural disasters in China, which is the primacy of meteorological disasters. North China is not only China’s political, economic and cultural center, but also an important grain production base in China, while the region belongs to warm temperate semi-arid and semi-humid monsoon climate, uneven distribution of precipitation, interannual variability, which makes meteorological drought frequency rank first in the country. From 1980 s until now, the drought is growing in North China. Since the late 1990 s, successive droughts came, which has become an important limiting factor for the steady increase in food production of this area. In order to alleviate the impact of meteorological drought on crops, the extraction of groundwater for irrigation in North China has become the main measure for drought-resistant capacity. A large area of extraction of groundwater, resulting in the rapid decline in groundwater levels caused severe hydrological drought. Based on this, the present study is to analyze meteorological drought composite index(CI), standardized precipitation evapotranspiration index(SPEI), standardized precipitation index(SPI), the applicability of precipitation Z index in North China region, select the appropriate drought index, using 69 meteorological stations data from 1961 to 2013, analyze the different time scales in North China, different seasons, different age occasion, different levels of spatio-temporal variation of meteorological drought and strength characteristics. Analyze the main causes of meteorological drought in North China from the three aspects such as geographical features, changes in atmospheric circulation and global change. On the basis of fully understanding the temporal and spatial variation and the characteristics and causes of meteorological drought in North China, grasping the occurrence and development of the law, to provide scientific support for the North China drought assessment and management of water resources, so as to improve the efficiency of agricultural water(groundwater) and ensure food in North China high capacity, provide protection for national food security. The main conclusions are as follows:(1) By EOF analysis shows that precipitation in North China representative stations were selected for Zhangjiakou, Qinglong, Nanyang, Juxian and Tarzan, temperatures representative stations were Xixia, Zunhua, Weixian and Wutai Mountain. By contrast CI, SPEI, SPI and Z index for different regions in North China, spring, summer, autumn, winter and monthly scales characterize drought conditions indicate, CI, SPI and Z can not be a good index to characterize the entire North China at all time scales meteorological drought conditions, there is a big error calculation results. Four kinds of drought index calculated from 9 representative meteorological stations in North China by Chinese meteorological disaster ceremony statistics show that in the four study partitions, SPEI index characterizing the drought conditions coincide with the actual highest rate, respectively, 57.41%, 60.78%, 57.06% and 66.99%. Comprehensive study results show that, SPEI index to characterize different time scales of various regions in North China meteorological drought best, Z index worst.(2) Over the past 53 years of SPEI values for different regions in North China shows a downward trend, the northwestern mountains, Jing-Jin-Ji, Henan and Shandong Peninsula with an annual average SPEI index were 0.17/(10a), 0.14/(10a), 0.07/(10a) and 0.10/(10a) of the rate decreases. In the 0.05 confidence level, the northwest mountainous and Jing-Jin-Ji areas the average SPEI occured in 1986 and 1991 mutations, but uncertain, very significant mutations occurred in Shandong Peninsula in 1975, while in Henan average SPEI is not mutated. In North China, drought has occurred in spring, summer, autumn, winter and monthly scales. The most severe drought in summer, winter and autumn fall followed. In terms of decadal variations, with the drought in the 1990 s the most severe drought since 2000 followed. In terms of spatial distribution showed the frequency of droughts in scales from north to south of the distribution. On the four seasons, drought mainly occurred in the northwestern and southeastern of Henan, northwestern Shandong of Peninsula, Shanxi, central and southern of Hebei and Jing-Jin regions. The drought intensity of overall strength characteristics of drought in North China is strong northwest and southeast, the northeast and mid-west droughts strength is weak. In North China of the extreme, moderate and mild drought frequencies occur at 0%~5.64%, 11.32%~22.64% and 5.66%~28.30%, mainly in the arid western of Henan, Shanxi, central-north of Hebei, Jing-Jin areas. The whole areas in three different levels of drought occurrence periods average annual scale were 70.6, 6.1 and 7 years. In terms of the four seasons, the spring of extreme drought, summer of moderate drought and autumn of mild drought are three levels of drought occur most frequently. The whole regions scale drought season average occurrence periods were 65.4, 6.5 and 6.4 years. Monthly scale extreme drought occurs mainly in the Shandong Peninsula, eastern of Henan, north and southwest of Shanxi, moderate drought occurs mainly in Jing-Jin-Ji and northwestern mountainous regions, mild drought occurred in Henan, Shandong Peninsula, southern of Shanxi and southern of Hebei regions, The average period of the whole region scale drought month were 90.9, 6.1 and 5.9 years.(3) Main reason in terms of the characteristics of the geographical environment for the formation of meteorological drought in North China’s is: The warm temperate semi-arid and semi humid monsoon climate zone, most areas in the leeward slope and water resources shortage; In terms of changes in atmospheric circulation, the major the reason of meteorological drought in North China’s is: monsoon and ENSO events occurrance. The drought index value was significantly increased with intensitively increasing of North China regional summer monsoon, while weakening the drought index value was significantly decreased. In addition, some area of ENSO intensity and precipitation in North China was a significant negative correlation between the declined in rainfall intensity increases when precipitation rises weakened. ENSO events in the entire North China intensity and air temperature was a significant positive correlation between the intensity increases when the temperature is on the rise, there is a downward trend when the temperature decreases. El Ni?o which has lifted the trend of temperatures, La Ni?a on the temperature has decreased; The impact of global change on meteorological drought in North China is mainly manifested in two aspects of urbanization and global warming. Urbanization leads to a significant probability density distribution of temperature shifts to higher temperature, resulting in precipitation reduce the city and the surrounding area. Global warming cycles 5% ENSO events, the North Pacific decadal changes weakened, POD frequency to high frequency mobile, resulting in significantly increased frequency of ENSO events, the East Asian summer monsoon weakened, resulting in a decrease in precipitation in North China lead to drought. |
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