Surface energy balance and the partitioning of sensible heat flux(SHF) and latent heat flux(LHF) play key roles in land–atmosphere feedback. However,the lack of long-term observations of surface energy fluxes,not to ...Surface energy balance and the partitioning of sensible heat flux(SHF) and latent heat flux(LHF) play key roles in land–atmosphere feedback. However,the lack of long-term observations of surface energy fluxes,not to mention spatially extensive ones,limits our understanding of how the surface energy distribution has responded to a warming climate over recent decades(1979–2009) at the national scale in China. Using four state-of-the-art reanalysis products with long-term surface energy outputs,we identified robust changes in surface energy partitioning,defined by the Bowen ratio(BR = SHF/LHF),over different climate regimes in China. Over the past three decades,the net radiation showed an increasing trend over almost the whole of China. The increase in available radiative energy flux,however,was balanced by differential partitioning of surface turbulent fluxes,determined by local hydrological conditions. In semi-arid areas,such as Northeast China,the radiative energy was transferred largely into SHF. A severe deficiency in near-surface and soil moistures led to a significant decreasing trend in LHF. The combined effect of increased SHF and decreased LHF resulted in significant upward trends in the BR and surface warming over Northeast China. In contrast,in the wet monsoon regions,such as southern China,increased downward net radiation favored a rise in LHF rather than in SHF,leading to a significant decreasing trend in the BR. Meanwhile,the increased LHF partly cancelled out the surface warming. The warming trend in southern China was smaller than that in Northeast China. In addition to impacts on heat-related events,the changes in the BR also reflected recent cases of extreme drought in China. Our results indicate that information regarding the BR may be valuable for drought monitoring,especially in regions prone to such conditions.展开更多
Introduction:Water such as precipitation is the most critical environment driver of ecosystem processes and functions in semi-arid regions.Frequency and intensity of drought and transient waterlogging are expected to ...Introduction:Water such as precipitation is the most critical environment driver of ecosystem processes and functions in semi-arid regions.Frequency and intensity of drought and transient waterlogging are expected to increase in the meadow steppe in northeastern China.Using a 4-year dataset of eddy covariance flux measurements,ground measurements of biomass,phenology,and meteorological conditions,we investigated the changes in energy fluxes at multiple temporal scales and under different precipitation regimes.Results:The meadow steppe was latent heat(LE)dominated when soil water content was>0.3 m3 m−3,but switched to sensible heat(H)dominated status when soil water content fell below 0.3 m3 m−3.LE dominated the energy exchange of the meadow grasslands on a yearly basis.Intensive precipitation had a profound impact on water-energy balance that could reduce the damages of drought by elevating deep soil moisture.The influence of LE on waterlogging depended on timing,with increased LE at the beginning of growing season and decreased LE after waterlogging.Spring and summer droughts resulted in different energy partitioning between latent and sensible heat energies,with spring drought dramatically decreased the LE fraction due to the change in water.In contrast,summer drought had little impact on LE due to the sufficient water input from large precipitation events at the beginning of the growing season.Conclusions:There existed great seasonal and interannual variabilities in energy balance and partitioning in the meadow steppe over the 4-year study period,which were strongly influenced by changes in precipitation.The water loss through latent heat was more sensitive to spring drought than to summer drought,while summer drought had negligible impact on LE.Waterlogging contributed to LE by enhancing its values during and after the waterlogged periods at the beginning of the growing season in a dry year,but lowering its value after the waterlogged periods in growing season.展开更多
基金supported by the Natural Science Foundation (NSF) of Jiangsu Province,China (Grant No.BK20140046)the NSF of China (Grant No.41375100)
文摘Surface energy balance and the partitioning of sensible heat flux(SHF) and latent heat flux(LHF) play key roles in land–atmosphere feedback. However,the lack of long-term observations of surface energy fluxes,not to mention spatially extensive ones,limits our understanding of how the surface energy distribution has responded to a warming climate over recent decades(1979–2009) at the national scale in China. Using four state-of-the-art reanalysis products with long-term surface energy outputs,we identified robust changes in surface energy partitioning,defined by the Bowen ratio(BR = SHF/LHF),over different climate regimes in China. Over the past three decades,the net radiation showed an increasing trend over almost the whole of China. The increase in available radiative energy flux,however,was balanced by differential partitioning of surface turbulent fluxes,determined by local hydrological conditions. In semi-arid areas,such as Northeast China,the radiative energy was transferred largely into SHF. A severe deficiency in near-surface and soil moistures led to a significant decreasing trend in LHF. The combined effect of increased SHF and decreased LHF resulted in significant upward trends in the BR and surface warming over Northeast China. In contrast,in the wet monsoon regions,such as southern China,increased downward net radiation favored a rise in LHF rather than in SHF,leading to a significant decreasing trend in the BR. Meanwhile,the increased LHF partly cancelled out the surface warming. The warming trend in southern China was smaller than that in Northeast China. In addition to impacts on heat-related events,the changes in the BR also reflected recent cases of extreme drought in China. Our results indicate that information regarding the BR may be valuable for drought monitoring,especially in regions prone to such conditions.
基金by the Major State Research Development Program of China(2016YFC0500600,2017YFE0104500)Natural Science Foundation of China(31800512,31870466),and the US-China Carbon Consortium(USCCC).
文摘Introduction:Water such as precipitation is the most critical environment driver of ecosystem processes and functions in semi-arid regions.Frequency and intensity of drought and transient waterlogging are expected to increase in the meadow steppe in northeastern China.Using a 4-year dataset of eddy covariance flux measurements,ground measurements of biomass,phenology,and meteorological conditions,we investigated the changes in energy fluxes at multiple temporal scales and under different precipitation regimes.Results:The meadow steppe was latent heat(LE)dominated when soil water content was>0.3 m3 m−3,but switched to sensible heat(H)dominated status when soil water content fell below 0.3 m3 m−3.LE dominated the energy exchange of the meadow grasslands on a yearly basis.Intensive precipitation had a profound impact on water-energy balance that could reduce the damages of drought by elevating deep soil moisture.The influence of LE on waterlogging depended on timing,with increased LE at the beginning of growing season and decreased LE after waterlogging.Spring and summer droughts resulted in different energy partitioning between latent and sensible heat energies,with spring drought dramatically decreased the LE fraction due to the change in water.In contrast,summer drought had little impact on LE due to the sufficient water input from large precipitation events at the beginning of the growing season.Conclusions:There existed great seasonal and interannual variabilities in energy balance and partitioning in the meadow steppe over the 4-year study period,which were strongly influenced by changes in precipitation.The water loss through latent heat was more sensitive to spring drought than to summer drought,while summer drought had negligible impact on LE.Waterlogging contributed to LE by enhancing its values during and after the waterlogged periods at the beginning of the growing season in a dry year,but lowering its value after the waterlogged periods in growing season.
