| The energy exchange between the surface and the atmosphere,such as net radiation,sensible heat flux,and latent heat flux,is one of the main energy sources driving atmospheric motion.The process of land surface energy exchange indirectly characterizes the energy forcing effect of solar radiation on the atmospheric system.Therefore,exploring the spatial-temporal changes in the net surface radiation,sensible heat flux,and latent heat flux in the region and their driving factors is of great significance for people to deeply understand the formation and change process of weather and climate in the region and even a large area.The loess Plateau has its unique underlying surface characteristics and high intensity of human activity interference.At the same time,it is deeply affected by the East Asian monsoon.The rainfall variability is large,which makes the ecological environment in this region extremely fragile.Extreme weather events are frequent.Human activity is extremely sensitive.Therefore,it is necessary to analyze the impact of the regional surface energy exchange process on regional climate,to understand the causes of regional climate change,and to formulate adaptive strategies for the region to adapt to global climate change.This study uses the newly verified ERA5 reanalysis data from the European Mesoscale Meteorological Forecasting Center(ECMWF)to analyze the temporal and spatial changes of the components of the surface energy balance system on the Loess Plateau and their effects on regional warming/cooling,and affects the surface factors affecting the energy budget are analyzed.Aiming at the determination of the two main influencing factors of climate change and land cover change,this study uses a new generation of typical land surface process model,EASS(Ecosystem-Atmosphere Simulation Scheme),to quantitatively reveal land cover and climate conditions contributions in energy balance.The main conclusions are as follows:(1)In the past 30 years,the multi-year averages of surface net radiation flux,sensible heat flux and latent heat flux on the Loess Plateau were 71.3 W/m2,28.94 W/m2,and 41.52 W/m2,respectively.-0.024 W/m2,0.14 W/m2,and-0.161 W/m2,respectively.In general,the interannual changes of each energy balance component are small.Among them,the net radiation and latent heat flux show a decreasing trend and the sensible heat flux shows an increasing trend.During the study period,except for the annual mean value of sensible heat flux fluctuating in spring and summer,the annual mean values of net surface radiation and latent heat flux in summer were significantly higher,followed by spring and winter being the smallest.(2)During the study period,the annual average value of ?(Rn-LE)in the Loess Plateau for many years was 1.683 W/m2,indicating that the project of returning farmland to forests and grasslands has a positive effect on atmospheric heat.The surface of the Loess Plateau in spring and summer has a positive effect on atmospheric heat(3.513 W/m2,4.969 W/m2);in autumn and winter,the surface of the Loess Plateau has a negative effect on atmospheric heat(-1.057 W/m2 and-0.453 W/m2).Before and after the project of returning farmland to forests and grasslands on the Loess Plateau,January,February,September,November,and December the ground surface had a negative effect on atmospheric heating.In March-August and October,the ground surface has a positive effect on atmospheric heating.(3)The correlation between NDVI and latent heat flux is the highest,which is 0.6(p<0.01);the correlation between NDVI and net surface radiant flux is the second;and there is no correlation between NDVI and sensible heat flux.Similar to NDVI,the correlation between precipitation and latent heat flux is the highest,with a correlation coefficient of 0.86(p<0.001),followed by the correlation with the net radiant flux on the surface,with the least effect on sensible heat flux.(4)The impact of climate change on surface energy distribution on the Loess Plateau is greater than that of land cover change.On an annual scale,changes in climatic conditions and land cover in the Loess Plateau both result in less energy being allocated to sensible heat fluxes and more energy to be distributed in latent heat fluxes,and changes in climatic conditions affect latent heat fluxes and the effect of sensible heat flux distribution is greater than land cover change.The impact of climate change and land cover change on the net surface radiation flux in the southeast of the Loess Plateau is quite different.The influence of land cover change on the surface net radiation flux in the southeast of the Loess Plateau is dominant.At the seasonal scale,the areas where land cover has a significant effect on net surface radiation are in the north and southeast of the Loess Plateau.Land cover change caused the sensible heat flux to decrease in most areas of the Loess Plateau.The impact of land cover change on the latent heat flux in the Loess Plateau area was mainly in the southeast region,and it had a greater impact on the latent heat flux in summer.Climate change has a greater impact on the surface net radiation flux in the Loess Plateau in spring and summer.In general,the effects of climate change on sensible heat flux and latent heat flux are greater than those of land cover in spring,autumn,and winter;in summer,both of them affect net surface radiant flux and latent heat flux and the effect of heat flux is small. |
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