Study On Water Balance Of Typical Moraine-dammed Lake

As an important part of earth's surface and climate systems,the cryosphere is a sensitive indicator of climate change.Glaciers and glacial lakes are important components of the cryosphere.There are wide distribution,a large number of water storage and significant and frequent exchanging of matter and energy.They have some significant impact on atmospheric circulation,surface runoff,water-cycle of the Earth,crustal movement of sea-level change and evolution of the natural environment.Furthermore,glacial lakes play an extremely important role in the fragile plateau eco-environment because they are sensitive indicators of climate change in alpine cold areas and can be a source for mountain outburst flood or cause mudflow disaster.This study based on topographic maps,remote sensing images,glacier inventory data and observation data of Longbasaba.The temporal and spatial variation characteristics have been analyzed on glaciers and glacial lakes of Geiqu basin in recent 30 years.The lake basin shape of Longbasaba glacial lake has been simulated.We calculated and analyzed the changes of various factors of water balance of Longbasaba glacial lake and coupling relationship and mechanism among climate change,glaciers and glacial lakes.The major results of these studies are as follows.(1)2016,the Geiqu basin has 95 glaciers,total area about 125.92 km~2,ice volume about 9.89 km~3.Development of most glaciers are those area between 0.1~0.5 km~2,concentrated distribution between 5900~6000 m,mainly in the north slope.In addition,Geiqu basin have 29 glacial lakes,total area is 4.05 km~2,concentrated distribution altitude about 5400~5800 m,small scale glacial lakes(<0.1 km~2)were developed widely,glacial lakes have expanded continuously.After 2016,the rate of expand was to speed up significantly.Using the model that is calculated glacial lake outburst probability to calculating the probability of glacial lake outburst in Geiqu basin.We find that the probability of outburst is 0.296 in Longbasaba glacial lake,according to the model manual that the probability of outburst is very high.(2)The monitor regularly in Longbasaba glacial lake found that climate has obvious seasonal characteristics in the lake region.The temp starts to lower in August every year,the minimum temperatures present in the middle of the next year on January.The temperature start raise in the end of February,the rate is 0.15?/d.In addition,the Longbasaba basin has been simulated through using the data about depth of glacier lake measurement.The volume of Longbasaba glacial lake is about 0.61×10~8 m~3.Water level monitoring found that lake water level is influenced by regional hydrological characteristics also has obvious seasonal.By analyzing the variation of many annual area and length,we find that the glacier lake area and length changes with high consistency.The glacier lake expanded along the direction of glacial retreat.There have important heat exchange process between glacial lake and glacier,and it should speed the melting ice up.(3)Through the calculation and analysis of water balance factors in Longbasaba glacial lake,we found that watershed area is 42.64 km~2,but glacier area accounted for70.61%of total area and the lake watershed area is 12.22 km~2,only 28.66%of the total area in the basin.If ignoring the groundwater recharge or infiltration and error,the glacial lake outlet flow remained at 1.84×10~3 m~3/d in the cold and dry season,and it shows a rapidly increasing trend after entering the rainy season,average daily flow of 9.44×10~5 m~3 and the average raise rate is about 3.42×10~4 m~3/d.Through the water balance equation we have calculated the proportion of glacial lake water balance factors in the Longbasaba.We found that precipitation is only 0.07%of total revenues and glacier meltwater runoff is accounted about 99.93%;the outlet flow plays an intensely prominent role in total expenditure,and it accounted about 99.56%.The surface evaporation is only 0.44%of total expenditure in Longbasaba glacial lake.(4)There is an obvious seasonal that water balance process in Longbasaba glacial lake.During December to next February,the lake freezes,the overall energy negative balance.Affected by the west wind circulation,the Longbasaba glacial lake region into dry season,rainfall,glacial runoff and solar radiation are reduced.In the process of dynamic balance,as feedback for lake water balance dynamic,the glacial lake reduces the outlet flow.At the end of April to October,the south Asian monsoon strengthens gradually.It bring the warm current that make this region into the rainy season and main bring short-term heavy rainfall,this will cause the Longbasaba glacial lake volume increases,and the warm climate also increases the ice surface temperature,accelerating melting glaciers.