Modeling Of Hydrological Processes In Cold Regions And Its Application In Songhua River Basin

Cold regions cover about 25%of the land area in the world.The Qinghai-Tibet plateau,northwestern alpine area,and Northeastern China are the three major cold regions of China.They cover about 43.5%of the total land area,of which 30%is permafrost,and 70%are seasonal frozen soil.The impermeability of frozen soil changes its capacity for surface storage,infiltration,and evaporation;this influences the hydrological cycle processes of the land surface.Meanwhile,global warming has led to shrinking glaciers and the degeneration of permafrost.These changes alter the runoff generation processes and runoff amounts of these regions,which in turn affect their water supply capacity.Hydrological modeling has become a powerful tool to research hydrological processes.However,the frozen soil modules in some hydrological models are often simplified that can hardly meet the simulation accuracy,and it can hardly applied in the large scale.Therefore,exploring the hydrological cycle under frozen soil conditions is very important for water resource management and effective utilization of water resource in cold regions.Northeast China is the main grain producing areas and heavy industry base of China.A large number of projects will be set up gradually,which brings challenge to protect regional water resources.This paper is aimed to research on the modeling of hydrological processes in the cold region and its application in Songhua River Basin(SRB).The model will be used to forecast the hydrological processes and support for the management of water resources.It is of great importance to protect national food security and water security.The main contents and results are as follows:(1)This paper analyzes the variations of maximum frozen depth of soil(MFDS),temperature,precipitation and discharge in SRB based on the observations.The results showed:(1)The annual mean temperature of SRB is gradually declining from south to north,and the annual precipitation gradually increase from west to east.(2)The MFDS of SRB showed increasing from south to north.The annual average MFDS is 174cm,and variation rate was-8.25cm/10a.The response of climate change is later in the North than that in the South.MFDS abrupt changes appeared in the year 1985,the MFDS decreased 35cm after abrupt.When the temperature of the basin is increased1?,the MFDS is decrease about 15cm.(3)The average discharge of the Jiamusi station was669.42×10~8m~3 from the year 1956 to 2000,and it showed a not significantly reduced trend.(2)The experiment was set up to study the water-heat transfer of frozen soil during freezing and thawing periods.In this paper,a multi-layer soil water-heat coupled model was built.The results showed that:(1)The moisture of surface soil layer was frozen after evaporation.The water migrated from unfrozen soil to frozen soil,and accumulated on top of the frost zone.(2)Tracer ions migrated with soil water and dissolved out during the freezing period.(3)A physical multi-layers soil water-heat coupled model was built to simulate the freezing and thawing processes of frozen soil.The model can effectively simulate the distributions of the soil temperature and water content.The average root mean squared errors of the temperature,unfrozen water content,total water content,and freezing depth of the soil were 1.21°C,0.035cm~3/cm~3,0.034cm~3/cm~3,and 17.6cm,respectively.The average Nash–Sutcliffe coefficient of the soil temperature was 0.92.(3)The Water and Energy transfer Processes in Cold Regions(WEP-COR)model is an improved version of the Water and Energy transfer Processes in Large basins(WEP-L)model that integrates a multi-layer frozen soil model to simulate the hydrological processes in cold regions and the heatfluxes at different depths of frozen soil.The WEP-COR model was validated by the measured results of stations.The results showed that:The simulations generally matched the observed results well.The average relative error(RE)of monthly discharge modeling was within10%and the average Nash–Sutcliffe coefficient was beyond 0.75.The RE endpoint of daily discharge showed a 35.04%decrease during thawing period.The he model performance was obviously improved when coupled with a frozen soil scheme.(4)According to the simulation results of the WEP-COR model,the distribution of frozen soil and the driving effect of climate change on frozen soil and runoff were quantitatively analyzed.The results showed:(1)The annual MDFS of the SRB decreased from the year 1956 to 2010.The MDFS contour of 150cm swing to the northwest.The change rate of longitude and latitude were-0.168°/10a and 0.156°/10a.The main temperature factor,which causes the MDFS change,is the accumulated temperature during freezing period.(2)The number of days of freezing and thawing periods increased from south to north.The contour of 180days swing to the northwest,the longitude and latitude were-0.157°/10a and 0.236°/10a.The main temperature factor,which causes the change of freezing and thawing time,is negative accumulated temperature.(3)The average annual discharge showed decreasing trend.The average discharge showed increasing trend during freezing and thawing periods.The precipitation showed the same tendency with discharge.(4)The water resources quantity showed a decreasing trend.The proportion of groundwater resource showed a decreasing trend.(5)This paper modeling the future variation of frozen soil and hydrological processes based on the forecast results of the regional model RegCM3.0.The result showed that:(1)The average annual precipitation and annual air temperature of the SRB from the year 2020 to 2050 are529.79mm and 4.26?,the change rate are-14.46mm/10a and 0.45?/10a.(2)The annual MDFS is 147cm,and the number of days of freezing-thawing periods is 163days,with a rate of-3.718cm/10a and-5.73days/10a.(3)The average annual discharge of the SRB showed decreasing trend.The trend variation of the discharge is different with precipitation during freezing-thawing periods.(4)The water resource is decreasing with the rate of-13.147×10~8m~3/10a.The proportion of groundwater resource is a decreased during thawing period and increase in other periods.