Spatial-temporal Variation And Attribution Analysis Of Total Primary Productivity, Evapotranspiration, And Water Use Efficiency In The Huaihe River Basin

Gross primary productivity(GPP)and evapotranspiration(ET)are important components of carbon-water cycle.Water Use Efficiency(WUE)closely integrated the carbon cycle and the water cycle,and it is an important indicator for evaluating the carbon-water cycle and vegetation water consumption.The variation characteristics of GPP,ET and WUE and their influencing factors as well as their responses to climate change have obvious regional differences.Huai River basin is an important agricultural production base in China,which consumes a lot of water and has important carbon sequestration capacity.At present,the distribution and influencing factors of GPP,ET and WUE in the Huai River Basin are not fully understood,and the changes of GPP,ET and WUE in the base under the future warming situation are still unknown.Thus,GPP,ET and WUE of the Huai River Basin were evaluated from 1981 to 2019 based on BEPS(Boreal Ecosystem Productivity Simulator)model using vorticity-related station data,meteorological data,remote sensing data,and literature data.The main factors affecting GPP,ET and WUE of the Huai River Basin were determined in terms of attribution analysis.At last,the possible impact of different warming conditions on GPP,ET and WUE was further explored.These results will deepen the comprehensive understanding of the change patterns of GPP,ET and WUE and their responses to climate warming,and will provide a reasonable reference for the rational use of water resources and dealing with the future climate change in the Huai River Basin.(1)The comparison of BEPS results with flux observation data and other different models results showed that the BEPS model could accurately simulate the changes of GPP and ET in the Huai River Basin.The annual average GPP and ET of the Huai River Basin from 1981 to2019 were 838.3 g C m^-2 and 558.67 mm,respectively.Both of GPP and ET showed upward trends,and the change rates were 9.49 g C m^-2 yr^-1 and 4.52 mm yr^-1,respectively.GPP and ET were the largest in summer,followed by spring,autumn and winter.Spatially,the highest values of GPP and ET were observed in the central-eastern and southern regions.Both of GPP and ET were on the rise in most areas of this base.The center of gravity model showed that the growth rate of GPP in the west area was greater than that in the east area,but the growth rate of ET in the south area was greater than that in the north area.The changes of GPP and ET were most directly affected by the leaf area index,followed by air temperature,both of them applied positive forces on GPP and ET.(2)The annual average WUE in the Huai River Basin from 1981 to 2019 was 1.48 g C kg H₂O^-1,and it showed a upward trend with a change rate of 0.0048 g C kg H₂O^-1 yr^-1.WUE in autumn and summer was slightly higher than that in winter and spring.Spatially,WUE exhibited the distribution characteristics of"high in the east and low in the west,high in the south and low in the north".The WUE in the southeast and south areas showed a decreasing trend,while the rest areas of this base showed an increasing trend.The center of gravity model showed that the increase rate of WUE in the northwest area was slightly higher than that in the southeast area.Leaf area index,precipitation,and relative humidity had positive effects on WUE,while air temperature and solar radiation had negative inhibitory effects on WUE.The increase of leaf area index was the decisive factor that caused a significant increase of WUE in this base.(3)The warming sensitive simulation results showed that the increase of average annual air temperature in the Huai River Basin by 0.5,1.0 and 2.0°C would increase GPP by 0.58,1.28 and 2.44%,ET by 1.98,3.92 and 7.69%,WUE by 0.75,2.26 and 4.50%,respectively.From the perspective of seasonal variation,the order of the effects of regional warming on regional GPP and ET was winter(promotion)>spring(promotion)>autumn(promotion)>summer(promotion).While the order of the effects of regional warming on regional WUE was summer(inhibition)>autumn(inhibition)>spring(inhibition)>winter(promotion).