| In order to explore the water transformation law among precipitation,soil water and runoff in hilly area of the southern Ningxia,water conservation forest of Luotuolin catchment in hilly areas of Southern Ningxia was selected as the research area,the study used the precipitation pattern of the last 50 years in hilly area of the southern Ningxia and the nature of soil percolation in the study area as the basis,and applied the hydrogen and oxygen isotope and water balance principles to investigate the transformation law between the "three waters" in the area,with a view to providing a theoretical basis for the water cycle theory and water utilization in hilly area of the southern Ningxia.The main conclusions are as follows:(1)In the past 50 years,the rainfall in the study area was mainly concentrated from June to September,and the annual rainfall was in the form of a single front.The absolute value of linear variation of annual rainfall is greater than the linear variation of annual rainfall days,the degree of variation of annual rainfall days is greater than the annual rainfall days,and the average rainfall intensity increases.In the past 50 years,the rainfall of light rain,moderate rain and torrential rain in Liupanshan area showed a downward trend,the rainfall of heavy rain showed an upward trend,and the number of days of light rain,moderate rain and torrential rain decreased.In Guyuan area,the rainfall of light rain,heavy rain and torrential rain increased,and the rainfall of moderate rain decreased;The number of days with heavy rain and torrential rain increased,the number of days with light rain and moderate rain decreased,and the number of extreme rainfall increased.(2)Fitting the hydrogen and oxygen relationship line to get the local atmospheric precipitation line as δD=6.01δ18O-5.26,,influenced by the degree of imbalance of water and vapor two-phase,and the influence of drought,its slope and intercept are shifted from the atmospheric precipitation line in China and the global atmospheric precipitation line.Using the three-terminal source mixing model,the recharge ratio of precipitation,surface water and soil water in the river is obtained as 69.5%,24.6%and 5.9%.(3)The mean values of δD and δ18O of precipitation-surface runoff-soil water showed a trend of precipitation>runoff>soil water in 0～20cm soil layer>soil water in 20～40 cm soil layer,which shows that the evaporative fractionation effect of precipitation is the largest,and the evaporative fractionation effect of soil water in the 20-40cm soil layer is the smallest The influencing factors of δD and δ18O are rainfall,sunshine hours,humidity,temperature,and the greater the rainfall,the more enriched δD and δ18O;the δD and δ18O are inversely proportional to the sunshine hours and temperature,and are directly proportional to the humidity;(4)The slope and intercept of hydrogen and oxygen relation lines of different precipitation types are smaller than the average level in China,and the slope relationship is moderate rain(<10 mm),light rain(10-25 mm)and heavy rain(25-50 mm),whereas the two-phase evaporation of water and vapor is the most unbalanced.The intercept relationship is small rain>medium Rain>heavy rain;the closer the water vapor source of heavy rain to the low latitude sea level;(5)Using the ratio of hydrogen and oxygen isotopes,combined with the water balance equation,the soil water flow,cumulative surface runoff,cumulative rainfall,and cumulative evapotranspiration in the study area from July to August were calculated to be 709.65 mm and 209.65 mm,145 mm,258.40 mm,respectively. |
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