Climate Change And Hydrological Response In Qinghai Lake From The Little Ice Age Based On GIS

Lakes are recorders of the past climate change and indicators of the modemenvironmental change.Qinghai Lake,the largest inland salt lake in China,located inthe northeast of Qinghai-XiZang(Tibetan)Plateau and semi-arid region where isunder the influence of westerly and Asia Monsoon,it is sensitive to climate change,therefore is of great importance in the study of the uplifting of the Qinghai-XiZangPlateau and global environmental change.Previously,numerous of scientificachievements have been made.But the lake level continues to be disputed because thedata is lack and the climate of Little Ice Age is still unclear.In past 50 years,the lakelevel has obviously ebbed.Unfortunately,due to the lack of field observation,littlehas been known about the water surface evaporation,which is the only way of losingwater for this inland lake.Modem lake evaporation is calculated withmended-and-extended Penman formula and relationship equation is constructedbetween evaporation and its driving forces on the basis of analyzing meteorologicaldata from six weather stations around Qinghai Lake.The lake level during the LittleIce Age is obtained by field investigation and geomorphologic analysis andprecipitation during the Little Ice Age is calculated using hydrological and energybudget model and the methodology of meteorology,hydrology and other softwaresuch as GIS,ERDAS.In summary,the dissertation including the following fourrespects:1.The tendency of air temperature is increasing obviously from 1960 to 2007,especially more strongly in winter and autumn.The obvious increase in airtemperature begins 1986,and the dramatic increase happens after 1997.It dropslargely in the early and mid-1980s.In precipitation,the tendency of its year andsummer is increasing weakly and autumn is reducing slowly.It is the least in 1970sand the most from 1986 to 1989.There is an abrupt decrease in 1990 and it hasbecome more in recent years.There are different precipitation variations in differentplaces.In the evaporation pan,the tendency of its year,spring and summer hasdecreased distinctly for 1960-2005.It is the most in 1970s and the least in 1980s.There is an abrupt decrease in 1981 and since then it drops continuously and has risen in the late 1990s.Qinghai Lake can moderate the extent of climate change bycontrasting meteorological elements between near and far from it.There are the sametrends of climate change both in Qinghai Lake basin and the whole plateau.Theclimate transition to warm and wet in the western of China can be detected in thisbasin.Relationship among meteorological elements shows:there is not the consistentrelation between air temperature and precipitation from 1960 to 2007,however,thepositive relation in some time represents.There is a negative relation betweenprecipitation and evaporation.The evaporation is not adding with the air temperatureascending.It is found that the reduction of sunshine duration,the increase of watervapor pressure and the lowering of wind speed have caused the decrease of theevaporation.These three factors play different roles in different places.So it isdifficult to explain the variation of the evaporation if the only factor is considered.There is a positive relation among total cloud amount,low cloud amount andprecipitation,but there are not clear relations between cloud amount and othermeteorological elements.In all,there are intricate non-linear relations amongmeteorological elements and they have the strong regional features.The further studymust be done to understand the cause of modem climate change in this basin.2.The monthly and annual evaporation of the lake are calculated from 1960 to2006 and the results show:the average value of 47 years is 924.3mm and there is noobvious variation tendency as the evaporation pan has.It is more exact consideringthe impact of the underwater heat flux on the water body.The polybasic linearequation indicates that sunshine percentage is the most important one and cloudamount and water pressure are more important ones and wind speed and airtemperature are important ones in contributing factors making for the variation of theevaporation.Qualitative and quantitative analyses denote that relationship betweenevaporation and temperature need to be reconsidered in climate change.Water budgetcalculating show the reason of having dropped 3.36m of the level from 1959 to 2007that the lake is losing 3.1×10⁸m³ per year.The calculating values of lake evaporationand water balance prove that it is feasible method which is used to understand waterevaporation in terms of mending Penman formula based on specific conditions.Theprecipitation plays the most important role in fluctuation of the lake level.In addition, it is stated that the dropping of the lake level which eco-environmental effects havebeen caused by and human activities have brought indirect effects on.3.The former conclusion reflects the fluctuation of the lake level is the bestindicator to the variation of precipitation,so,evidences that the fluctuation of lakelevel have left can be used to study the past climate change in this basin.In-situinvestigations indicate there are eight and seven lakeshore bars in Erlangjian andHaiyanwan around Qinghai Lake respectively.Elevations of lakeshore bars inErlangjian are 3195.1m,3196.5m,3203.8m,3204.2m,3204.5m,3205.8m,3208.5m,3210m from the lake to the land and the top five ones are formed in contemporarytimes and others in ancient times.Elevations of lakeshore bars in Haiyanwan are3195m,3196.5m,3198m,3199m,3201m,3202m,3203.8m from the lake to the landand they all are formed in contemporary times.The ¹⁴C dating of the fish bones at3198m and the bird bones at 3201m in Haiyanwan are 440±40 a B.P.and 200 a B.P.respectively,which indicates that the climate in 440±40 a B.P.is drier than in 200 aB.P..This result has been proved by relative research done by other people.Moreover,the ¹⁴C dating of the deadwood at 3201m of a lakeshore bar in Hadawan is 195 a B.P.,so the lake area of Qinghai Lake and precipitation can be estimated by the proofcoming from the level and age of lakeshore bars in Haiyanwan and Hadawan.Thelevel in 200 a B.P.is 8m higher than that of today and the precipitation in that time is416mm,which is 9% higher than that of today.4.The lake areas are obtained in different times and levels on the basis of theformer research and elevation data about the lake.As a result,it is preliminarilythought that there is not high lacustrine shoreline in the early Holocene and 100mshorelines above the present lake level are formed by tectonic movement becausewhen the lake level arrives beyond 3300m it is connected to the water system ofHuangshui River through Kutu pass basin,but lacustrine sediments are not found inthe east of Kutu pass basin.