Based on stable hydrogen and oxygen isotope data (�´18O, �´D) and meteorological\nobservation data for complete hydrological annual precipitation from 2016 to 2017 in the monsoon\nmarginal region of northern China (Fengxiang and Ningwu), the isotopic characteristics of\nprecipitation and the sources of water vapor in these two regions combined were studied. The results\nshowed that �´18O and �´D values in the wet season (June through September) were higher than in the\ndry season (October to May of the following year) in Fengxiang and Ningwu. The intercept and slope\nof the meteoric water line in the two regions were somewhat low, revealing that the water vapor in the\nrainfall comes mainly from the tropical ocean. On a synoptic scale, significantly positive correlations\namong dry season precipitation, �´18O, and temperature manifested temperature effects, but in the\nwet season, the temperature effect was not significant. On a monthly scale, a relationship did not\nexist between the change in trend of the average value of monthly weighted �´18O in precipitation and\nthe average temperature change value in the two regions. However, in the wet season, significantly\nnegative relationships can be found between the average monthly weighted �´18O in precipitation\nand rainfall amount, which indicated a remarkable rainout effect. Further investigation revealed\nthat continuous precipitation made the values of �´18O and �´D more negative under the same source\nof water vapor (the rainout effect). Because the annual rainfall in the monsoon marginal region\nof Northern China is mainly made up of monsoon rainfall, the oxygen isotope index of geological\nand biological records, such as stalagmites and tree rings, which inherit meteoric water isotope\ninformation, can be used to reconstruct past rainfall changes in northern China.
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