| As one of the most hazardous natural disasters,drought disaster seriously threatens the security of food production and agricultural development.As a major grain-producing province and an important commodity grain base,Heilongjiang Province is the ballast stone for maintaining national food security.There are many irrigation areas in the Naoli river basin,which is an important grain producing area in Heilongjiang Province,and the study of drought characteristics and causes in the Naoli river basin irrigation areas is important for guiding drought prevention and drought relief work and promoting agricultural production and development.Therefore,eight irrigation districts,namely Qiliqin Irrigation,Youyi Irrigation,Daxing Irrigation,Hamatong Irrigation,Jinan Irrigation,Bawusan Irrigation,Longtouqiao Irrigation and Wujiuqi Irrigation,were selected as typical irrigation districts in the Naoli River Basin,and the standardized precipitation evapotranspiration index SPEI,standardized soil moisture index SSI and standardized runoff index SRI were used to characterize meteorological drought,agricultural drought and hydrological drought,respectively.Based on the output data of SWAT model,the above three single drought indices were calculated to construct the comprehensive drought index OCDI.Analysing the spatial and temporal variation characteristics of the regional hydrological cycle elements and different types of droughts in typical irrigation areas of the Naoli River Basin,and analyzing and evaluating the causes of different drought types.The main research findings are as follows:(1)The annual precipitation,spring and winter precipitation in the typical irrigation area of Naoli River basin from 1967 to 2017 showed an increasing trend of 2.2mm/10 a,9.06mm/10 a and3.18/10 a,respectively,and a decreasing trend of-2.89mm/10 a and-7.06mm/10 a in summer and autumn,respectively.The first main cycle of interannual and spring,summer,autumn and winter precipitation are 16 a,25a,15 a,15a and 10 a,respectively.Annual runoff,spring and summer runoff showed increasing trends of 1.78m3/s,4.51m3/s and 0.32m3/s per 10 a,respectively,and autumn and winter runoff showed decreasing trends of 2.69m3/s and 0.41m3/s per 10 a,respectively.The first main cycles of interannual and spring,summer,autumn and winter runoff are 16 a,26a,15 a,16a and 15 a,respectively.Soil water content and spring,summer,autumn and winter seasons soil water content showed an increasing trend of 75.42mm/10 a,23.36mm/10,15.80mm/10 a,16.45mm/10 a and 17.23/10 a,respectively.The first main cycle of interannual and spring,summer,autumn and winter soil water content was 17 a,18a,17 a,17a,17 a.Annual evapotranspiration,spring and summer evapotranspiration showed increasing trends of 1.55mm/10 a,6.66mm/10 a and2.34mm/10 a,respectively,while autumn and winter evapotranspiration showed decreasing trends of-6.94mm/10 a and-0.44/10 a,respectively.The first main cycle of interannual and spring,summer,autumn and winter evapotranspiration was 17 a,17a,25 a,16a and 14 a,respectively.The distribution of precipitation,runoff,soil water content and evapotranspiration within a typical irrigation area shows an increasing distribution from southwest to northeast.(2)The annual scale SPEI12,summer and autumn scale SPEI3 of the typical irrigation area in the Naoli River basin from 1967 to 2017 showed a decreasing trend of-0.066/10 a,-0.105/10 a and-0.145/10 a,respectively,with an aggravated trend of meteorological aridification,and an increasing trend of 0.121/10 a and 0.3/10 a for spring and winter scale SPEI3,respectively with a decreasing trend of meteorological aridification.The first main cycle of interannual and spring-summerautumn-winter scale SPEI are16 a,25a,6a,15 a and 11 a,respectively.The annual scale SSI12 and the four seasonal scales SSI3 of spring,summer,autumn and winter showed an increasing trend of0.175/10 a,0.208/10 a,0.13/10 a,0.135/10 a and 0.145/10 a,respectively with the trend of agricultural aridity was mitigated.The first main cycles of interannual and spring,summer,autumn and winter seasons SSI are 17 a,18a,17 a,17a and 17 a,respectively.The annual scale SRI12,spring and winter scale SRI3 showed increasing trends of 0.1/10 a,0.368/10 a and 0.015/10 a,respectively with the trend of hydrological aridity was alleviated,while the summer and autumn scale SRI3 showed decreasing trends of-0.002/10 a and-0.019/10 a,respectively with the trend of hydrological aridity was aggravated.The first main cycles interannual and spring-summer-autumn-winter SRI are 16 a,18a,16 a,16a and 16 a,respectively.three single drought indices showed spatial variability in trends and magnitude of tendency rates in typical irrigation areas.(3)The constructed integrated drought index OCDI can effectively identify and assess the integrated drought situation in the Naoli river basin,and has good applicability.The annual scale OCDI12 and the three seasonal scales OCDI3 of spring,summer and winter in the typical irrigation area of Naoli River basin from 1967 to 2017 showed increasing trends of 0.076/10 a,0.375/10 a,0.004/10 a and 0.212/10 a,respectively,and the comprehensive aridification migtigatory trend was more obvious in the western and northern of the typical irrigation area.The autumn scale OCDI3 showed a decreasing trend of-0.042/10 a,and the comprehensive aridification aggravateing trend was more obvious in the eastern of the typical irrigation area.The first main cycles interannual and spring-summer-autumn-winter OCDI are 16 a,17a,16 a,16a and 16 a,respectively.(4)There are correlations and resonance cycles between precipitation,runoff,soil water content,evapotranspiration,AO index,NOI index,PDO index,relative sunspot number and different types of drought indices in the typical irrigation area of the Naoli River basin.The influence of regional hydrological cycle elements on the formation of different types of droughts in typical irrigation areas of the Naoli River basin is greater than the influence of climatic factors and sunspot activity.The main drought-causing factors of meteorological drought are precipitation,runoff and evapotranspiration.The main drought-causing factors of agricultural drought are soil water content,runoff and evapotranspiration.The main drought-causing factors of hydrological drought are runoff,soil water content and precipitation.The main drought-causing factors of comprehensive drought are precipitation,soil water content and runoff.AO,ONI,PDO and sunspot activity indirectly affect different types of droughts by influencing regional hydrological cycle processes.(5)Based on the results of drought characteristics and causes of drought in typical irrigation areas in the Naoli River Basin,the following countermeasures for drought mitigation in irrigation areas are proposed: strengthen the construction of agricultural water conservancy engineering facilities and maintenance of existing engineering facilities in irrigation areas;develop dry farming and promote scientific and advanced irrigation measures;strengthen water resources utilization management and optimal allocation to improve water resources utilization efficiency;establish and improve drought disaster information system and strengthen drought prediction;improve drought prevention and drought relief service system and raise level of drought prevention and relief work. |
