Understanding altitudinal temperature variations using a surface energy balance approach

 

High-altitude regions are argued to react more strongly to global warming compared to low-altitude regions. However, due to a combination of feedback mechanisms, micro-climatic trends, and lack of long-term observational data, elevation-dependent warming has been difficult to understand and quantify. We address this question using a surface energy balance approach where 2m air temperature variations along altitudes are quantified following changes in surface radiation and turbulent fluxes.  The turbulent fluxes in the energy balance are constrained using the thermodynamic limit of maximum power. The downwelling longwave radiation is parameterized using the semi-emperical equation by Brutsaert (1975). We used BSRN (Baseline Surface Radiation Network) and FLUXNET dataset to test our approach and found that daily variations in 2m air temperatures reasonably well (with R2 value of 0.75) along the altitude gradient. We find that for high altitudes, the downwelling longwave radiation is lesser compared to stations at low altitudes at similar latitudes for both all sky conditions and clear sky conditions. We attribute it to less absorptive mass above the high altitudinal setting, leading to lower atmospheric emissivity and changes in lower atmospheric heat storage. On the other hand, absorbed solar radiation when normalized by potential solar radiation, shows strong seasonality, which is influenced by albedo changes and water vapor content in the atmosphere.  Future work entails extending this framework to get a physically based estimate of elevation-dependent warming using the sensitivity of temperature to components in the energy balance. This understanding is crucial for anticipating the impacts of warming on water resources and ecosystems in these regions and, consequently, for developing effective adaptation and mitigation strategies.