Paleoclimatic researches have revealed that the East Asian summer monsoon (EASM) strengthened and precipitation increased in north China during the early to middle Holocene. The lacustrine landform and sediment recorded approximately simultaneous Holocene high lake levels. However, relatively few studies have been reported involving the quantitative reconstruction of precipitation and lake areas in the Mu Us Desert (MUD), northwest edge area of the modern EASM. Based on the lacustrine landform, and by using the lake hydrologic model, this study quantitatively reconstructed precipitation and lake areas during the early to middle Holocene in the MUD. The results revealed the following: 1) A total of 127 paleolakes existed in the closed drainage area during the early to middle Holocene. The area of paleolakes was 896.1 km 2 , which is 2.96 times that of modern lakes. The relative height between the highstand and the modern lake surface is ∼5–9 m. 2) Precipitation during the early to middle Holocene decreased from 550 mm in the southeast to 350 mm in the northwest. The 400 mm isohyet moved 130–170 km to the northwest, roughly coincident with the modern 250 mm isohyet. 3) The relative increase in precipitation was ∼32–60%, and the increase in the west was significantly higher than in the east. The precipitation gradient in much of the MUD was lower than the present. The results show that the monsoon edge area and monsoon rain belt migrated to the northwest during the early to middle Holocene. The MUD was stably dominated by the EASM. Data also showed that the spatio-temporal pattern of the climate during the early to middle Holocene was relatively humid with a decreased precipitation gradient for millennia.
Erosion pins is widely used to measure the wind and water erosion,but the accuracy of this method is relatively low because this method is usually impacted by human activities.The black soil region in Northeast China is suffering from soil erosion due to intense reclamation in the middle of 20 century,and gully erosion in this region is very severe.However,the previous researches were mainly focused on the changes of the entire gully.It is difficult to monitor the changes at a certain site inside the gully and few research were focused on this problem.In this paper,we try to use the GIS points as the virtual erosion pins instead of the real erosion pins to monitor the erosion and deposition process at the bottom of gully in Hebei catchment in Heilongjiang Province.Virtual erosion pins were not affected by the environment,human activity and ground settlement.The precision of the gully’s DEM can reach the cm-level examined by the checkpoint method,which was used to this research.The annual variation of the bottom of gully monitored by the virtual erosion pins combining with the high precision gully DEM consist with the regular gully development by the previous study.The results prove that using virtual erosion pins combining with high precision DEM to monitor the annual variation of gully bottom is valid.From the DEM we found that the head part of the gully incised intensely.The mid-part is the main place of the deposition in the dry years,and the incision is relatively weaker than the head part of the gully at the wet years,because the runoff’s sediment transport capacity reaches the saturation level while the flow velocity decreases due to the increasing width of the gully.The end of the gully is relatively stable because the runoff and sediment has reached a relative equilibrium state.
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