Surface protrusions of the microstructured lizard skin may reduce evaporation intensity: Numerical modelling approach

Evaporative water loss is a critical challenge for terrestrial organisms, particularly those inhabiting arid environments. Many lizards including geckos and chameleons possess nanoscopic hairlike setulae or surface protrusions that may reduce evaporation by modifying the local microclimate near the skin. To investigate this effect, we numerically modeled water evaporation from a substrate covered by periodically structured surfaces mimicking such biological features. The model employs a diffusion equation with a heterogeneous diffusion coefficient and incorporates wind-driven advection to account for external air flow. Simulations were performed for both uncapped and capped pillar structures. Results show that the presence of periodic pillars alone modifies local vapor transport, creating vortices and zones of enhanced humidity near the substrate. The presence of caps on the pillar tops substantially enhances this effect, maintaining higher vapor density in the substrate-proximal region and reducing the net evaporation flux. Evolution of total evaporation reveals that capped structures reduce water loss by 2-3 times compared to uncapped configurations. These effects arise since the microstructured surface shapes the boundary layer, which slows down diffusion, creates humid air traps, and redirects wind-driven transport. Our findings highlight the functional role of surface microstructures in controlling evaporation and suggest a mechanistic explanation for the evolution of nanoscopic hairs in the groups of lizards with especially thin skin. The study also provides design principles for biomimetic surfaces aimed at passive water conservation and microclimate control.