生态恢复背景下非辐射效应主导的黄土高原生长季地表温度变化

Non-radiative effect dominates surface temperature changes on the Loess Plateau during the growing season under the background of ecological restoration

作为人类活动影响气候变化的重要因素之一,土地利用主要通过改变地表生物地球物理过程和生物地球化学过程来影响气候系统。土地利用通过生物地球化学过程对气候系统的影响已得到广泛和深入研究,但对生物地球物理过程认识仍不足,这不利于区域气候的准确评估。本研究针对经历过大规模高强度人类活动的黄土高原地区,利用地表辐射能量数据,在明确2000—2015年耕地转移情况的基础上,量化了耕地和林草地的生物地球物理差异,然后结合能量再分配因子估算了退耕还林还草的辐射和非辐射效应,最后利用非辐射效应指数(NRFI)量化了地表温度变化中非辐射效应的贡献率。结果表明:土地利用变化对地表温度变化影响的辐射效应表现为增温效应(0.05℃),非辐射效应表现为降温效应(0.21℃),非辐射效应占主导;在研究期间,生长季地表温度下降了0.17℃,非辐射效应贡献率为69.7%;地表温度变化对能量再分配因子、地表反照率和土壤热通量等敏感性不同,其中,能量再分配因子对地表温度的变化起决定性作用,使得生长季地表温度下降了0.21℃。本研究不仅为准确评估土地利用变化对区域气候影响提供理论依据,也对黄土高原地区应对或减缓气候变化的影响具有重要意义。

As one of the important factors affecting climate change by human activities,land use changes mainly affect climate system by changing the surface biogeophysical and biogeochemical processes. The impacts of land use change on climate system through biogeochemical processes have been extensively examined,but the understanding of biogeophysical processes is still insufficient,which is not conducive to accurate assessment of regional climate. This study focused on the Loess Plateau that has witnessed large-scale and high-intensity human activities. Based on the surface radiation energy data,the transfer of cropland from 2000 to 2015 was defined. The biogeophysical differences between cropland,forest,and grassland were quantified. Combined with the energy redistribution factor,the radiative and non-radiative effects of returning cropland to forest and grassland were estimated. Finally,we used the non-radiative forcing index( NRFI) to quantify the contribution of the non-radiative effect to the changes of land surface temperature.Our results showed that land use change caused 0.05 ℃ warming through the radiative effect and0.21 ℃ cooling through the non-radiative effect on local surface temperature change. The nonradiative effect dominated responses of local temperature to land use change. During the study period,land surface temperature in the growing season dropped by 0.17 ℃ and the contribution of non-radiative effects was 69. 7%. Surface temperature changes showed different sensitivity to energy redistribution factors,surface albedo,and soil heat flux. The energy redistribution factor dominated the land surface temperature change and reduced the surface temperature in the growing season by 0.21 ℃ . Our results provide a theoretical basis for accurately assessing the influence of land use changes on regional climate and have implications for coping with or mitigating the impacts of climate change in the Loess Plateau.