| Drought was the most common form of meteorological disasters in the world. It had a huge impact on the industry and the lives of people. To have a deeper understanding of the drought and reveal the distribution characteristics, the cause of the drought, we employed comprehensive Meteorological drought index(CI) and regional drought intensity to analyze the temporal and spatial distribution characteristics and influencing factors of meteorological drought in Dongting Lake Basin. It used the daily meteorological data and NCEP reanalysis data. The meteorological data included 84 meteorological stations from 1962 to 2013 in Dongting Lake Basin. The article analyzed temporal and spatial distribution characteristics of meteorological drought by using the trend analysis method, Morlet wavelet analysis and so on. By comparing the daily maximum temperature, rainless days and maximum continuous rainless days, the 500 hpa geopotential field anomaly, the western Pacific subtropical high indices, the vapor flux, vapor flux divergence and polar vortex indices in dry and wet years, the article analyzed the influence factors of drought. The results showed that:(1) The intensity of regional drought was obvious mainly in summer, autumn, summer to autumn, autumn to winter. Among then, the regional drought intensity tended to increase in spring, summer, summer to autumn and winter. The average drought intensity of continuous drought was heavier than that in single season. According to the Morlet wavelet analysis, it showed the regional drought intensity had quasi-periodicity of 5 years, 10 years and 22 years. Among then, the 10 years was the obviously primary period, the 5 and 22 years were the secondary periods. The range of drought stations ratio total stations of four seasons in the basin was mostly floated from 10%-30%, presenting mainly as local drought and part of the regional drought. And the range of drought was generally wider in summer and autumn. High incidence of drought frequency mainly occurred in summer, summer to autumn and autumn, which was located in the south mountainous area and northeast of Basin.(2) The regional drought intensity were inversely correlated with the average days of high temperature, no rain days. Among them, the correlation between regional drought intensity and no rain days was higher than that with days of temperature. In summer and fall, the correlation between rainless days, days of the high temperature and regional drought intensity was greater than other seasons. The rainless days of summer and fall were greater than that in other seasons. In terms of drought and flood years, average days of high temperature and average rainless day in drought year were more than that in flood years at the same period for four seasons. On the spatial distribution, average rainless days was more in the northern of Dongting Lake Plain and mountain in the south in the majority for four seasons in drought year and wet years.(3) In terms of the global scale of atmospheric circulation and water vapor transportation, geopotential height anomaly was local opposite in spring and winter in drought and flood years, which was opposite at overall situation in summer and autumn. Geopotential anomaly was given priority to positive anomaly area in the basin in drought year, and it was given priority to negative anomaly in the basin in flood year. As for subtropical high index, in winter and spring, western Pacific subtropical high in wet years was stronger than that in drought years. In autumn, subtropical high indices in drought year were greater than that in wet year. The West ridge line of subtropical high were easternmost in spring, in summer and in winter in drought years, which was opposite in autumn. In terms of polar vortex index, intensity and area of polar vortex was strongest in winter, which was second in the spring and the weakest in summer. In drought and flood years of the four seasons, wet years was affected more by polar vortex rather than that in dry years.(4) Water vapor flux generally in drought year was smaller than that in wet years. As for four seasons in Hunan province, water vapor flux was largest and had most transport channel in the summer, then it was moderated in spring and autumn, and least in winter. The water vapor water vapor transport channel were mainly across from the equator by the Arabian Sea- bay of Bengal- south or north of Indochina in spring, summer and winter. And it was mainly across from Indian Ocean- the Bay of Bengal –Hunan. In drought years, water vapor flux divergence mainly diverged in Dongting Lake Basin. In wet year, it was given priority to with convergence in Dongting Lake Basin. The convergence center and divergence center of water vapor flux was corresponding to strong water vapor transport center in a certain extent. |
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