Influences Of Multi-source And Multi-resolution DEMs On Glacier Simulation In Karola Pass

Quaternary is the recent geological period to the present modern times.Affected by the glacial-interglacal cycles,large-scale glaciers developed on the Qinghai-Tibetan Plateau,leaving behind abundant glacial landforms.These glacial remains are the direct evidence of the cryospheric changes in the past,which have been widely used to reconstruct palaeo glaciers,as well as palaeo climate and environmental and conditions.The Karola Pass is located on the northern slope of the Himalayas,controlled by south Asian monsoon and westerlies.Quaternary glaciers in this area have left glacial landforms with clear outlines and series.This thesis reconstructed palaeo glaciers around the Karola Pass during the Little Ice Age,Neoglacial,Early Holocene,and the Last Glacial Maximum using the improved glacial flowline modeland based on four types of digital elevation models(DEMs),including ALOS PALSAR RTC HIGH RES 12 m DEM,ASTER 30 m GDEM,SRTM 30 m DEM,SRTM 90 m DEM.The reconstructed palaeo glaciers can be used to estimate glacier area,volume,and thickness during each period and derive the Equilibrium Line Altitude(ELA)in each stage by the Accumula t io n Area Ratio(AAR)method.This paper analyzes the impacts of diffrent DEMs to the changes of estimated glacier area,volume,glacier thickness and ELA,as well as paleoclimat ic characteristics estimated using the relationship between annual mean temperature and precipitation at ELAs of glacier(P-T relationship).This thesis also discusses the impact of galcier change on regional water resources,which is critical in predicting the future impact of galcier change on water resources.The major conclusions as follows:(1)Our results indicated that glaciers are not sensitive to subtle DEM elevation changes because of plastic rheology.It seems that ALOS 12 m DEM provides too much higher resolution,while SRTM 90 m DEM provides too much lower resolution terrain data for the glacier flowline model.Both these two types of DEMs result in relatively large differe nces between simulated glaciers and measured data.In contrast,the 30 m DEMs produce relative ly better glacier simulations compared to measured data,suggesting that such resolution is consistent with the scale of glacier plastic rheology.In comparison of SRTM 30 m DEM and ASTER 30 m GDEM,the simulations using SRTM 30 m DEM have relatively higher accuracy,likely due to its relatively higher data quality.(2)The impacts of different DEMs on simulated glaciers are apparently more significant in volume and thickness than in area and ELA.The coefficients of variation in simulated glacier volumes were 2.4% ? 9.0%,and 2.6% ? 7.6% for Karola ice cap,,and Kaluxung Glacier,respectively,since the LGM.The coefficients of variation in simulated ice thickness were 1.2%? 7.5%,and 1.9% ? 8.0%,respectively,for these val eys since the LGM.Our results also indicated that the influences of DEMs on simulated glaciers decreased with the increased glacier size.Specifically,simulated glacier areas,volumes,thicknesses,and ELAs tend to become stable for different DEMs during the LGM when glaciers are much larger.(3)Based on the P-T model,the reconstruction results of temperature and precipitat io n conditions of glaciers around Karola Pass showed that the precipitation in the last glacia l maximum was 40%?80% of the present,and the simulated temperature drop values of ALOS12 m DEM,ASTER 30 m GDEM,SRTM 30 m DEM and SRTM 90 m DEM were 3.4??8.1?,3.5??8.0?,3.7??8.1?,and 3.2??8.0?,respectively.The precipitation in the Early Holocene was 100%?110% of the present,the temperature drop values simulated by DEM were1.1??2.7?,1.3??2.7?,1.4??2.8? and 1.2??2.8?,respectively.The precipitation in the Neoglacial was 100%?110% of the present,the temperature drop values simulated by DEM were 0.7??2.1?,1.1??1.7?,0.9??2.1? and 0.8??1.9?,respectively.The precipitat io n in the Little Ice Age was 100%?110% at present,the temperature drop values simulated by DEM were 0.5?1.5?,0.2??1.3?,0.4??1.5? and 0.2??1.6?,respectively.(4)Different DEMs also affect the estimation of glacier changes on regional water resources.The relative differences between estimated water equivalent of glaciers using ALOS12 m DEM,ASTER 30 m GDEM,SRTM 90 m DEM and the value estimated using SRTM 30 m DEM are 13.8%,8.0%,and 5.0% during the LIA;17.0%,9.8%,and 7.0% during Neoglacia l;17.3%,9.8%,and 9.4% during Early Holocene;and 17.3%,6.3%,and 7.9% during the LGM,respectively.