| Drought is a natural disaster that occurs frequently on a global scale,and it has a major impact on social life and economic development.The Xiangjiang River Basin is the most prominent area for industrial,agricultural and socio-economic development in Hunan Province,covering most areas of Hunan's "Hengshaolou Arid Corridor",and is frequently threatened by drought.In this paper,the daily precipitation and temperature data of 14 weather stations in the basin in the past 58 years and the four drought indices of Dnp,Pa,SPI,and SPEI were used to analyze the temporal and spatial changes of drought in the Xiangjiang River basin.Wavelet analysis has studied the effects of climate elements,atmospheric circulation,and sunspot activity on drought,and has obtained the following main conclusions:(1)The average precipitation of Xiangjiang River Basin in the past 58 years is 1466mm.The large topographical differences in the basin are one of the important reasons for the uneven distribution of precipitation.The precipitation in the East and south mountainous areas and the southwest is rich,while the precipitation in the hills and basins in the West and the East is small.The main rainfall throughout the year is from March to August.Except for February,April,September,and October,precipitation is on the rise.The annual-scale precipitation shows an insignificant upward trend.The spring and autumn precipitation show a downward trend.The winter and winter precipitation showed an upward trend.The main period of annual precipitation change is 16 years,and that of spring,summer,autumn and winter is 4,11,5 and 16 years in turn.Autumn and summer have a wide range of precipitation changes,and the risk of drought is great.The average temperature of Xiangjiang River Basin is 17.4?,and the annual average temperature rises significantly.Except that the summer temperature rise trend is not obvious,the temperature in other seasons shows a clear upward trend.(2)Based on continuous non-effective precipitation days(Dnp)research,we know that the northern and western parts of the basin have the greatest risk of drought,and the annual drought risk in Guidong and Shaoyang is relatively large.The risk of drought occurrence has declined,increased,and decreased in 58 years.In each season of drought,the risk of drought in autumn is the highest,the frequency of drought is the largest,the scope of drought is the farthest,and the highest drought incidence is 62.07%.The frequency of summer drought and drought-prone areas is second only to that of autumn.The highest frequency of drought is 44.83%.Drought risk is greatest in the middle of the study area.The relative risk of spring drought and winter drought is small,and the frequency of winter drought is greater than that of spring drought;According to the study of the precipitation anomaly percentage(Pa),it can be seen that the annual scale drought frequency gradually increases from north to south.Among them,Jiahe and Chenzhou have the greatest drought risk in the south,and the risk,frequency and impact range of autumn drought are all in the four seasons.First,the drought frequency is as high as 40%,and the risk of autumn drought is greatest in the southern part of the basin.Summer drought frequency and impact range are close to autumn,the highest drought frequency is 28%,drought risk is concentrated in the northeast and southwest of the basin.The northeast and southwestern areas of the study area are at greater risk of drought.The relative risk of spring drought and winter drought is small,and the frequency of winter drought is slightly greater than that of spring drought.According to the study of the standardized precipitation index(SPI),the annual drought frequency is between 25.86%and 43.1%,and each drought level decreases sequentially from light to heavy,showing different spatial distribution characteristics.The drought frequency in the Xiangjiang River Basin is most widely distributed in autumn,and it is the highest in some areas in summer.Therefore,the drought risk in each season of the Xiangjiang River Basin is in descending order:autumn,summer,winter,spring;Based on the standardized precipitation evapotranspiration index(SPEI)study,it can be seen that the annual drought intensity is not significantly increasing.During the study period,the research area was mostly at the level of light and moderate drought.The areas with more annual drought were mainly distributed in the northeast and south of the research area.The annual drought risk in Zhuzhou,Daoxian and other places is relatively large,and the drought risk in Changning and Shuangfeng is relatively small.On the quarterly scale,the summer drought frequency is the largest,followed by autumn,and the study area shows arid trends in spring and autumn.The summer and winter showed a tendency of humidification.The stations with a higher risk of drought in spring were Hengyang and Jiahe;the stations with a higher risk of drought in summer were Nanyue;the stations with a higher risk of drought in autumn were Shaoyang and Xinhua;the stations with higher risk of winter drought For Huanghua and Jiahe.(3)The four types of drought index evaluation results compared with historical drought data are:The frequency of droughts in the Dnp index evaluation study area is significantly higher than the actual historical droughts,and the frequency of meteorological droughts at different time scales calculated by the Pa index is lower than in other seasons except autumn The frequency of droughts evaluated by SPI and SPEI is close to the actual drought.Comparing the two indexes,the latter is more consistent with the actual drought.Therefore,the SPEI index is the most applicable drought indicator in the Xiangjiang River Basin.(4)The causes of the drought in the Xiangjiang River basin are complex.Comparing the correlation between the SPEI index and precipitation and temperature,the drought in the Xiangjiang River basin is mainly caused by changes in precipitation;the horseshoe-shaped landform surrounded by mountains on three sides and opening northward in the Xiangjiang River basin has created climate diversity.The change trend of the summer SPEI index and the East Asian summer monsoon index shows good consistency.When the El Nino cold event occurs,the average SPEI is mostly negative.During the warm event,the SPEI average is mostly positive.Therefore,when the cold event occurs,the Xiangjiang River Basin Drought is more likely to occur.There is a resonance relationship between the occurrence of drought in the Xiangjiang River Basin and each atmospheric circulation index at a certain stage,but there are significant differences in time and frequency.The degree of influence of various atmospheric circulation factors on the drought in the Xiangjiang River Basin:SOI>NOI>AMO>NAO index,Therefore,the Southern Oscillation Index SOI has the most severe impact on the drought in the Xiangjiang River Basin.Sunspot activities not only have a significant impact on precipitation,temperature,and potential evapotranspiration,but also have significant effects on atmospheric circulation indexes such as the inter-decadal oscillation of the North Atlantic.Sunspot activities Become the main driving force for the formation of drought in the Xiangjiang River Basin. |
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