Spatial And Temporal Variation Of Surface Albedo In The Huaihe River Basin And Its Simulation Study

Land surface albedo is a key parameter to calculate the energy budget of surface radiation,which can significantly affect climate change by affecting the energy balance between the ground and the atmosphere.At the same time,land surface albedo is also an important parameter for land surface process model simulation.In this study,the sky scattering ratio factor was used to weight and calculate the black sky and white sky albedo in the short-wave band provided by MODIS land surface albedo climate grid product MCD43B3 from 2005 to 2015 to obtain the real land surface albedo reflection.The spatial and temporal distribution and variation characteristics of land surface albedo were analyzed by taking the Huaihe River Basin as a case study,which is located in the climate transition zone between north and south of China and is dominated by agricultural land.Based on the influence analysis of land use type,terrain,vegetation,land surface temperature and climate on land surface albedo,the grey correlation analysis method was introduced to overcome the interaction and independence of various factors,the influence degree of factors was objectively quantified and ranked.According to the ranking of influencing factors,different simulation experiments were designed,and the data of land cover type and fractional vegetation cover were applied to the Noah-MP land surface model,respectively,and the influence of different input parameters on the land surface albedo simulated by the model was discussed.The main conclusions are as follows:(1)From 2005 to 2015,the average annual land surface albedo of Huaihe River Basin showed an increasing trend,with an annual variation of 0.138-0.157,and there were significant seasonal differences.The average land surface albedo in summer was the largest,followed by spring,and the smallest in autumn.The average land surface albedo in summer and autumn showed an increasing trend,while the average land surface albedo in winter showed a decreasing trend,with the largest annual fluctuation.The monthly average land surface albedo of the basin ranged from 0.134 to 0.167.With the process of crop growth period,it increased first and then decreased,with the highest value of 0.167 in January,then decreased rapidly in February,and then rose again.It reached a small peak in July,then fell back,and reached the lowest value in October.The annual average land surface albedo in Huaihe River Basin displayed a spatial distribution pattern of " high in the north and low in the south,high in the east and low in the west ",varying from 0.043-0.223,with an average of0.145.The low-value areas were mainly concentrated in areas of water densely distributed?mountainous and hilly areas,and with the small standard deviation;the high-value areas were mainly concentrated in the central and eastern plain of the basin,and with the large standard deviation relatively.In 61.5% of the area,the land surface albedo showed an increasing trend with significant seasonal differences.(2)The land surface albedo in the Huaihe River Basin is affected by multiple influencing factors.There are obvious differences in land surface albedo for different land use types.The order of the land surface albedo of different land use types in the study area was: cultivated land>urban and rural,industrial and mining,residential land>grassland>forest land>water body,among which,the standard deviation of the land surface albedo of cultivated land,water area,urban and rural,industrial and mining and residential land was relatively large.Land surface albedo was affected not only by land use types,but also by topography,climate,NDVI,LST and other surface parameters.The monthly average land surface albedo was positively correlated with NDVI,LST,air temperature,and precipitation in most areas,and the area accounts for90.23%?82.32%?85.41% and93.70%,respectively.Under different land use types(except the water),the order of the annual average grey correlation degree between the land surface albedo and the influencing factors is: NDVI>air temperature>LST>precipitation,and the order of the spatial grey correlation degree is: NDVI>precipitation >LST> air temperature> Elevation.(3)The four sets of experiments: CTL_ALB(model data),LC_ALB(replacing land cover type data),FVC_ALB(replacing fractional vegetation cover data)and NEW_ALB(replacing the above two input data at the same time)were designed to simulate the surface albedo in the Huaihe River Basin in 2014.The results showed that all the four experiments could well simulate the annual variation trend of surface albedo in the Huaihe River Basin in 2014.On the whole,compared with the experiment CTL_ALB,the correlation coefficients of the other three sets of experiments were improved,the deviation and the root mean square error were reduced,all of which improve the overestimation of the model simulated land surface albedo to a certain extent,especially in winter,the improvement effect of the experiment NEW_ALB was the best,Both the deviation and the root mean square error were lower than CTL_ALB by 0.014,followed by FVC_ALB and LC_ALB.(4)From the spatial distribution of the simulated land surface albedo,the four sets of experiments can well reflected the spatial distribution characteristics of land surface albedo in the Huaihe River Basin,which was " high in the north and low in the south,high in the east and low in the west ".In most areas,the simulated values of each experiment were slightly lower than those of CTL_ALB,and the areas,where the simulated values of LC_ALB decreased significantly,were mainly related to the increase of urban construction land ratio for the replaced land cover type.The spatial distribution of the experiment FVC_ALB could reflect more information detail.It could be seen that the change of fractional vegetation cover data had more obvious impact on the land surface albedo simulation for the model.The experiment NEW_ALB that replaced the two kinds of input data at the same time obtained the most detailed and reasonable spatial distribution,which showed more improvement for the spatial distribution simulation of the land surface albedo.