Changes In Climate-and Glacial-Related Hydrology In Hala Lake Region,Qinghai Province,China

Tibetan Plateau is one of the largest and highest land masses in the world,also has the large amounts of ice,snow and permafrost,so it plays a crucial role for downstream hydrology and water availability in Asia.During the recent decades characterized by warming trend,the contrasting patterns(eg.climate-hydrology and glacial-hydrology processes)acted by the glacier and lake systems are caused by both local and global factors.The role of spatial and temporal heterogeneity of climate and climate change is aimed to be quantified in this study.Lake basins and their catchments in high mountain regions of the Tibetan Plateau(TP)react sensitively to any kind of climate and environmental change.Hence,the reconstruction of the water balance of Hala Lake region is of great significance.Hala Lake region(97°24'-97°47'E,38°12'-38°25'N)is situated in arid northeast TP.This individual system is under hot debate as the potential monsoon boundary,whilst in-situ measurements are non-existent in this region.This thesis uses the climate data to analyze,calculate and reconstruct the lake climate-hydrology and the basin glacial-hydrology in time series 1950 to 2010,based upon energy exchange between atmosphere and the underlying surface of the lake system,and the role of the various components of the energy and water balance.The reconstruction of the climate-hydrology and glacial-hydrology processes,specifically,the attempts are made to seek for the suitable mathematical models,methodologies and applications in ungauged basins,to realize the breakthrough in hydrological theory.Both qualitative and quantitative analysis are conducted in this study.Five factors obtained from the energy and meteorological field of Hala Lake region represent the topographical characteristics,moisture trransport,melting process,precipitation,and wind field,respectively.They can explain 98%of the variance.The quantitative analysis is based upon in-situ measurements in a large area,High Asia Reanalysis data,TRMM and Delaware reanalysis data.Monthly precipitation and temperature measured by the climate stations in adjacent areas are linearly regressed against Delaware grid data,to establish the seasonal functions.Models for simulating evaporation and glacier melt rate are developed based upon energy-and water-balance theory.The simulated annual precipitation and temperature is 247.7 mm and-5.3 ?.Precipitation and temperature are highly correlated.A constant increasing trend of temperature since 1956 continues until 2010.The annual land evaporation is 211 mm and the lake evaporation is 592.8 mm.The comparison between two different underlying surfaces turn out that they show no similar variation trend.The sensitivity analysis demonstrates that lake and the land evaporation are mainly controlled by radiation and precipitation respectively.In the glacierized area of Hala Lake region,the daily pattern of mean surface energy components shows that net shortwave radiation dominates energy input over the considered period followed by sensible heat flux.Energy output sinks at the glacier surface are melt energy,longwave radiation and latent heat flux.In order to simulate the meltwater from the glaciers,three statistical models including the temperature and radiation-indexes,which incorporate incoming shortwave radiation and albedo,are calibrated against the calculated melt rate based upon the energy-balance theory.The radiation-temperature-index models are more capable of simulating melt rate.The separation of the temperature-dependent and-independent energy fluxes shows the best model performance,with the highest coefficient of determination being 94.4%,amongst all models.The annual melt rate in north,east and south coast of Hala Lake are 540.8,486 and 320 mm.a-1,respectively.The annual melt volume is estimated 0.49x108 m3,with a high correlation with temperature.The significant decrease in 1955 divides the whole period into two phases.1985-2010 is characterized by the most rapid growth period,in which the melt volume are doubled from 0.47×108 m3 to 0.98×108m3.The water budget from 1950-1995 shows a stable trend with both positive and negative values,occasionally with high net water input in 1980 and 1990.Most of the years,the water surplus or deficit can compensate each other,with a large surface area,the lake level is stable.After 1995,the lake has a pronounced expansionary phase characterized by the continuous positive surplus with the value up to 3×108m3.a-1.Prediction in ungauged basins has become more popular all over the world.The study conducted in Hala Lake region 1950-2010,is of great importance not only to estimate the representation of hydrological series,but also to the researches on hydrological process and runoff estimation of an ungauged watershed in high altitude and cold regions.The thesis contributes to a further and detailed understanding of the energy and water balance components variation(both spatial and temporal)in a lake system of the Tibetan Plateau.It serves to increase knowledge on the reconstruction methodologies of meteorological data,and the mechanisms of an individual system.The findings are crucial for estimating future lake level evolution in regions without the monitoring system.It provides the reference for the further analysis and research on lake related water availability on the Tibetan Plateau.