Exploring Forest-Atmosphere Interactions Under Heat Extremes in a Semi-Arid Region

The potential effects of desert plantations, such as those used for climate change mitigation, during extreme heat waves remain an important and unresolved question. While the influence of large-scale surface heterogeneity, such as land-sea distribution and mountain ranges on weather, is well established and incorporated in operational numerical weather prediction models, the impact of smaller-scale heterogeneities remains uncertain. Specifically, the interplay between the synoptic forcing and the arising effects of mesoscale interactions is not yet fully understood.  

The Eastern Mediterranean and the Middle East face intensified heat and drought due to climate change, impacting regional weather and local ecosystems. Semi-arid forests, such as the Yatir pine forest on the edge of the Negev Desert, provide a unique lens through which to study land surface-atmosphere feedback, particularly under extreme heat events. 

Ongoing studies show that due to high incoming solar radiation and its low albedo, the Yatir Forest net radiation is higher than in any other eco-regions, balanced by a large sensible heat flux. Thus, the resulting cooler surface suppresses the emission of longwave radiation compared with the surrounding warmer shrubland. The thermal contrast between the forest and the surrounding shrubland can also result in the development of secondary circulations within the PBL. The combined effects of these processes significantly modify the surface-atmosphere energy exchange, can affect the forest microclimate, and, if extended to a larger scale, could potentially impact regional weather and climate.

This research investigates the interactions between the Yatir Forest and the atmosphere under dry heat extremes, focusing on mechanisms driving radiation dynamics, energy fluxes, and local circulations. Our approach combines in-situ measurements from the Yatir Forest, atmospheric reanalysis data, Lagrangian analysis, and high-resolution simulations using the ICON numerical weather prediction model. Through a series of numerical forest configuration experiments incorporating forest-atmosphere feedback, we examine the potential of semi-arid afforestation to influence boundary layer dynamics, exploring the implications for local and potentially regional moderation of extreme climatic events and sustainable land use. We incorporate the concept of the canopy convector effect for semi-arid regions to demonstrate the sensitivity of the numerical results to surface parameters and synoptic conditions causing heat waves.  

• Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel (yotam.menachem@weizmann.ac.il)