Vegetation-Driven Circulations and Their Modification During Heatwaves: Insights into the Downwind Impacts of Semi-Arid Forests in Peninsular India

Vegetation plays a crucial role during heatwaves by altering surface energy partitioning and influencing local to regional climate. In addition to the thermodynamic response of vegetation, the differential heating caused by sensible heat gradients across adjacent regions of vegetation and dry, bare soil can generate a mesoscale circulation akin to sea breeze-like circulation, known as a ‘vegetation breeze’¹, which redistributes heat and moisture and affects downwind regions. While the impacts of large‑scale heterogeneities such as land-sea contrasts and topography are well established, the influence of finer‑scale vegetation heterogeneity remains uncertain. This gap is critical because semi‑arid forests, covering nearly 18% of Earth’s land surface, are highly sensitive to heat extremes. Differences in their Bowen ratios can substantially alter surface energy budgets, producing varying levels of hydroclimatic stress under similar atmospheric forcing. Yet, their potential to amplify or mitigate the impacts of extreme heat events is still poorly understood.

This study focuses on the semi-arid deciduous forests of the Eastern Ghats in Peninsular India, which are part of the Nagarjulam Srisilam Tiger Reserve and neighbouring protected areas  located along the ecotone between the dry Deccan Plateau and the Eastern coast.  It is spread over 5 districts in Andhra Pradesh and Telangana which are known to experience extreme heatwaves. Our previous observational analyses show that these transitional forests are highly sensitive to climatic stressors, particularly through their land surface temperature (LST) and evapotranspiration responses. During heatwave events, we observed pronounced LST gradients between forested and adjacent non-forested areas, indicating strong surface thermal contrasts arising from vegetation-atmosphere interactions. Given the heightened climate sensitivity of these transitional ecosystems, it is essential to understand not only how these ecosystems respond to extreme heat but also how they may influence local atmospheric dynamics.

To address this, we investigate how vegetation driven circulations such as the ‘vegetation breeze’ and the canopy convector effect² emerge from land surface heterogeneity, and how these processes affect boundary layer processes and downwind thermal anomalies during heatwaves. Our approach combines atmospheric reanalysis data for large‑scale boundary conditions, satellite observations to characterize land surface and vegetation, and high‑resolution WRF simulations to resolve fine‑scale forest-atmosphere feedbacks. Through a series of forest‑configuration experiments, we assess the capacity of semi‑arid forests to alter boundary layer processes and explore the implications for local and regional modification of extreme events as well as downwind impacts. By isolating the role of semi‑arid forests during heatwaves, these experiments contribute to the mechanistic understanding of semi-arid forest-atmosphere interactions and their role in shaping hydroclimatic extremes under a changing climate.

 

References

[1] McPherson, R. A. (2007). A review of vegetation—atmosphere interactions and their influences on mesoscale phenomena. Progress in Physical Geography, 31(3), 261-285.

[2] Banerjee, T., De Roo, F., and Mauder, M.: Explaining the convector effect in canopy turbulence by means of large-eddy simulation, Hydrol. Earth Syst. Sci., 21, 2987–3000, https://doi.org/10.5194/hess-21-2987-2017, 2017.