Background:There is an urgent need for quantifying the terrestrial carbon sink in the context of global carbon emissions.However,neither the flux measurements,nor the national wood balances fulfil this purpose.In this...Background:There is an urgent need for quantifying the terrestrial carbon sink in the context of global carbon emissions.However,neither the flux measurements,nor the national wood balances fulfil this purpose.In this discussion article we point at various shortcomings and necessary improvements of these approaches in order to achieve a true quantification of the carbon exchange of land surfaces.Results:We discuss the necessity of incorporating all lateral fluxes,but mainly the export of biomass by harvest,into the flux balance and to recognize feedbacks between management and fluxes to make flux measurements compatible with inventories.At the same time,we discuss the necessity that national reports of wood use need to fully recognize the use of wood for energy use.Both approaches of establishing an ecosystem carbon balance,fluxes and inventories,have shortcomings.Conclusions:Including harvest and feedbacks by management appears to be the main requirement for the flux approach.A better quantification of wood use for bioenergy seems a real need for integrating the national wood balances into the global carbon cycle.展开更多
Actual evapotranspiration(ET)is a major component of the water balance.While several international flux measurement programs have been executed in the tropical rain forest of the Amazon,those measurements represent th...Actual evapotranspiration(ET)is a major component of the water balance.While several international flux measurement programs have been executed in the tropical rain forest of the Amazon,those measurements represent the evaporative process at a few selected sites only.The aim of this study is to obtain the spatial distribution of ET,using remote sensing techniques,across the entire Amazon River Basin.Results from six global ET products based on remote sensing techniques(GLEAM,SEBS,ALEXI,CMRSET,MOD16,and SSEBop)were merged to obtain an ensemble prediction of the ET rates for the complex and in-accessible environment of the Amazon at a spatial resolution of 250 m.The study shows that the basinwide average ET is 1316 mm/year with a standard deviation of 192 mm/year.This new ET-Amazon product was validated against seven different historic flux tower measurements.The energy balance closure of the in situ measurements varied between 86 and 116%.Only months with more than 70%completeness of in situ measurements were considered for validation.Different procedures for closure correction were included in the analyses.The correlation between measured and remotely sensed ET is good(R2>0.97 for consecutive periods of 2 to 12months),and the bias correction is negligible for the energy balance residual method,which seemed most favorable.Monthly ET values have more uncertainty.The monthly RMSE values vary between 7.4 and 27.8 mm/month(the average RMSE is 22.2mm/month),and the coefficient of determination(R2)varies between 0.48 and 0.87(the average R2 is 0.53).The ET from the water balance is 1380 mm/year,being−64 mm/year difference and 4.6%less than ET derived from the water balance.The evaporation from the Amazon basin inside Brazil is 5063 km3/year,followed by Peru with 1165 km3/year.ET-Amazon shows more spatial details and accuracy than alternative global ET products such as LandFlux-EVAL,Model Tree Ensemble(MTE),and WACMOS-ET.This justifies the development of new regional ET products.展开更多
文摘Background:There is an urgent need for quantifying the terrestrial carbon sink in the context of global carbon emissions.However,neither the flux measurements,nor the national wood balances fulfil this purpose.In this discussion article we point at various shortcomings and necessary improvements of these approaches in order to achieve a true quantification of the carbon exchange of land surfaces.Results:We discuss the necessity of incorporating all lateral fluxes,but mainly the export of biomass by harvest,into the flux balance and to recognize feedbacks between management and fluxes to make flux measurements compatible with inventories.At the same time,we discuss the necessity that national reports of wood use need to fully recognize the use of wood for energy use.Both approaches of establishing an ecosystem carbon balance,fluxes and inventories,have shortcomings.Conclusions:Including harvest and feedbacks by management appears to be the main requirement for the flux approach.A better quantification of wood use for bioenergy seems a real need for integrating the national wood balances into the global carbon cycle.
文摘Actual evapotranspiration(ET)is a major component of the water balance.While several international flux measurement programs have been executed in the tropical rain forest of the Amazon,those measurements represent the evaporative process at a few selected sites only.The aim of this study is to obtain the spatial distribution of ET,using remote sensing techniques,across the entire Amazon River Basin.Results from six global ET products based on remote sensing techniques(GLEAM,SEBS,ALEXI,CMRSET,MOD16,and SSEBop)were merged to obtain an ensemble prediction of the ET rates for the complex and in-accessible environment of the Amazon at a spatial resolution of 250 m.The study shows that the basinwide average ET is 1316 mm/year with a standard deviation of 192 mm/year.This new ET-Amazon product was validated against seven different historic flux tower measurements.The energy balance closure of the in situ measurements varied between 86 and 116%.Only months with more than 70%completeness of in situ measurements were considered for validation.Different procedures for closure correction were included in the analyses.The correlation between measured and remotely sensed ET is good(R2>0.97 for consecutive periods of 2 to 12months),and the bias correction is negligible for the energy balance residual method,which seemed most favorable.Monthly ET values have more uncertainty.The monthly RMSE values vary between 7.4 and 27.8 mm/month(the average RMSE is 22.2mm/month),and the coefficient of determination(R2)varies between 0.48 and 0.87(the average R2 is 0.53).The ET from the water balance is 1380 mm/year,being−64 mm/year difference and 4.6%less than ET derived from the water balance.The evaporation from the Amazon basin inside Brazil is 5063 km3/year,followed by Peru with 1165 km3/year.ET-Amazon shows more spatial details and accuracy than alternative global ET products such as LandFlux-EVAL,Model Tree Ensemble(MTE),and WACMOS-ET.This justifies the development of new regional ET products.
