Characteristics Of Meteorological Droughts In Ziya River Basin And Its Impacts On Hydrological Droughts

Under the background of global warming,the drought events occur frequently.The Ziya River is the second major water system of the Haihe River Basin which is one of the areas with high frequency in drought disaster in China.The drought disasters have greats effects on the development of the regional social economy and the improvement of the ecological environment.Based on the precipitation and temperature data of 6 meteorological stations and runoff data of 1 hydrological station in the Ziya River Basin from 1961 to 2013,this paper used the standard precipitation evapotranspiration index and standard runoff index to analyze the spatial and temporal distribution characteristics of meteorological droughts in the Ziya River Basin and the influences of the meteorological droughts on the hydrological droughts in the upper reaches of Hutuo River Basin.The conclusions were as follows:(1)Mann-Kendall trend test and Morlet wavelet analysis were used to analyze the variation trend and cycle characteristics of meteorological droughts at different time scales in the study area,and the spatial evolution characteristics were analyzed by using the ratio of drought stations and drought frequency.The results showed that the monthly,seasonal and annual SPEI decreased from 1961 to 2013.Since 1970,the study area was gradually featured with the trends of droughts.The monthly,seasonal and annual SPEI have a main period of 21~30 years and a sub period of 4~11 years.From the spatial perspective,the droughts were mainly focused on the local level.As to the frequency,it reached 28%~36% for the annual droughts,40%~60% for the spring droughts,and 30%~33% for the monthly droughts.As to the drought grade,the light droughts most frequently occurred.(2)Used the range theory to separate the two drought indicators(drought duration and drought intensity)from SPEI-1,optimized the Gumbel Copula function to establish a two-dimensional joint distribution function,and comprehensively revealed the characteristics of meteorological droughts in the Ziya River Basin from the joint probability and recurrence period of drought duration and drought intensity.The results showed that the joint probability,the joint recurrence period and the co-occurrence recurrence period of the two drought indicators were increasing with the increased values of drought duration and drought intensity,while the joint exceedance probability showed a decreasing trend.The combinations of different drought duration and drought intensity can lead to the same joint probabilit y,joint exceedance probability,joint recurrence period and co-occurrence recurrence period.The meteorological drought events with D 5 and S 4 in the Ziya River Basin have basically covered most of the drought events,and the joint recurrence period for most of the meteorological drought events was within 10 years.(3)Based on the monthly SPEI and SRI index,the effects of meteorological droughts on hydrological droughts in the upper reaches of Hutuo River were discussed by using the cross correlation time-delay analysis and the two-dimensional joint distribution model.The results showed that,the meteorological droughts were often accompanied with the hydrological droughts,and the latter was usually lagging behind the former.Meteorological droughts generally began in spring and ended in summer.Hydrological droughts began in spring,ended in summer,or began in late autumn and early winter,and ended in spring.When the drought events occurred over the basin,the hydrological drought level was usually lower than the meteorological drought level.