| Droughts occur frequently and have a wide impact.Droughts threaten China’s water resources security,food security and ecological security.In recent years,with climate change,extreme hydrological and extreme meteorological events have occurred frequently worldwide.The frequency and intensity of drought events are also increasing.The problem of water shortage in the basin has become more prominent.The shortage of water resources in the basin restricts the sustainable development of society and economy.Therefore,it is necessary to gain a deeper understanding of the drought evolution pattern,explore the mechanism of drought occurrence and development,and provide reference to guide the scientific drought resistance,early warning and response in the basin.The Haihe River Basin is located in North China.The basin suffers from"nine droughts in ten years",alternating droughts and floods,and shortage of water resources.These constraints have restricted the sustainable development of the Haihe River Basin.The Haihe River Basin is one of the basins with more serious droughts and floods in China.To carry out research on water science in the Haihe River Basin,it is important to understand the drought problems in the basin scientifically and identify the drought evolution and development.To this end,the thesis focuses on the drought problems in the Haihe River Basin.The thesis selects the measured hydrological and meteorological data of the Haihe River Basin from 1961-2019.The thesis takes a meteorological drought and hydrological drought perspective.The standardized precipitation evapotranspiration index(SPEI)and the standardized runoff index(SRI)are selected for the evaluation index.Several methods,such as the Mann-Kendall trend test,run theory,wavelet-based analysis and Copula functions are used to analyze the changes in drought events in Haihe River basin.In this work,we systematically assess the drought characteristics and their evolution,and identify typical meteorological and hydrological drought events,and then analyze the response relationships between meteorological and hydrological drought.It provides a reference for drought prevention and drought relief and scientific response in the basin.The main research results of the thesis are as follows:(1)Meteorological drought characteristics based on SPEIFirstly,the SPEI drought index series at different scales(1,3,6 and 12 months)were constructed by using the monthly meteorological observation data of 33 national meteorological stations in the Haihe River Basin.The results show that the monthly and seasonal SPEI is more sensitive to drought event identification,which is obviously affected by short-term precipitation and temperature.The SPEI of the semi-annual and annual scales is closer to the actual drought.Secondly,the trend shows that there are obvious differences in the drought trend of different stations.For example,the drought trend of Jining,Qinhuangdao and Bazhou has slowed down,while the drought trend of Yushe and Fengning has increased.The mutation analysis showed that there was a significant mutation around1965,which was obvious in winter at the seasonal scale and more prominent in the first half of the half-year scale.The periodic analysis results show that the monthly SPEI has a 4-year main cycle,and the main cycles of other scales are 1-2 years.In general,the meteorological drought shows short-period fluctuations.Furthermore,the run theory was used to identify meteorological drought events,and the drought characteristics were characterized by drought duration,drought intensity and drought frequency.The results showed that the drought duration became shorter,the intensity showed a’high-low-high’change,and the high-frequency drought was mainly mild drought and moderate drought,and local severe drought and extreme drought were concentrated.Finally,Copula function is used to fit the joint distribution between meteorological drought duration and intensity.The optimal fitting result of the joint distribution of meteorological drought duration and intensity in the southern part of the basin is Gumbel function,and the optimal fitting result in the central and northern parts is Clayton function.From the results of the combined return period,the return period of the meteorological drought characteristic value in the southern and central parts of the basin is within 20 years,while the return period in the northern part is within 50 years.The southern and central parts of the basin are more likely to suffer from meteorological drought than the northern part.(2)Hydrological drought characteristics based on SRIThe monthly measured runoff data of 8 typical control hydrological stations were used to analyze the evolution characteristics of runoff in the basin.The results showed that the annual runoff in each region of the basin showed a decreasing trend,among which Luanxian station had the largest decrease(annual average decrease of 2.13 m~3/s),and Sandaohezi had the smallest decrease(annual average decrease of 0.22 m~3/s).By constructing SRI drought series with different time scales,it was found that there were 8 stations in 1961-1963,four stations in 1990,2000 and 2011,and 3 hydrological stations in 12 years with severe and above drought at the same time.The statistical analysis of SRI sequences at different time scales shows that the trend of hydrological drought at most stations is not significant,but there are many significant mutation years,and the main periods of multiple stations are significantly different,ranging from 1-2 years to 5-6 years.According to the spatial distribution of drought duration,intensity and frequency,the long-duration drought mainly occurred in Luanhe River,the high-intensity drought mainly occurred in the north of the middle reaches of Luanhe River and Daqinghe River,and the high-frequency drought events were mainly mild and moderate,mainly in Chaobaihe River and Zhanghe River.The results show that the joint optimal fitting distribution of hydrological drought duration and intensity in the southern part of the basin is Frank function,and the optimal fitting distribution in the central and northern parts of the basin is Clayton function.The return period of hydrological drought eigenvalues in the southern and northern parts of the basin is within 20 years,while that in the central part is within 200 years.The hydrological drought in the southern and northern parts of the basin is more likely to occur than that in the central part.(3)Response relationships of different drought typesBased on the run theory,the meteorological drought and hydrological drought events were identified.The results showed that the meteorological-hydrological drought events characterized by the drought index at the 3-month scale were highly matched,including 17meteorological-hydrological drought events in the south,20 in the middle and 23 in the north of the basin.In terms of duration and intensity,the drought events in the southern and northern parts of the basin are more serious,and the duration and intensity of meteorological drought have a greater impact on hydrological drought.The Copula function is used to analyze the joint marginal distribution of meteorological and hydrological drought duration and intensity,and the optimal marginal distribution function and the joint distribution fitting between meteorological and hydrological drought characteristic variables are determined.The results show that the Gumbel function is more suitable for simulating the joint distribution of meteorological and hydrological drought,but the Clayton function performs better in the joint distribution of meteorological and hydrological drought duration at the observatory.Compared with meteorological drought indicators,hydrological drought indicators have a more direct impact on drought events in the basin.The southern and central parts of the basin are prone to short-term and moderate-intensity drought events,while the northern part of the basin is prone to short-term and high-intensity drought events. |
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