Beyond air temperature: An examination of leveraging operative temperature space for the discovery of bioinspired thermal design features.

Advancements in thermal management systems often rely on incorporating novel design features which can be effectively influenced through bioinspiration. A major gap in applying bioinspired concepts to thermal design is the identification of morphological structures of interest due to the multimodal nature of most energy transfer systems. Investigating species along an operative temperature gradient-which incorporates convective and radiative heat transfer-offers a more comprehensive view of environmental heat load than traditional ambient air temperature or latitude, providing better granularity to identify phenotypic plasticity driven by heat load. This study refined a thermally oriented bioinspiration search method by clustering species spatial group locations based on growing season operative temperature distributions. Focusing on the North American tree species Populus heterophylla, thermal clines were developed using a density-based cluster analysis utilizing ERA5-Land climate data to evaluate both 2-meter air temperatures and calculated operative temperatures. To evaluate phenotypic trends across these thermal regimes, 2D leaf margins from 103 herbarium specimens were analyzed for aspect ratio, leaf width, and non-dimensionalized characteristic edge radius. While ambient air temperature clustering yielded only two broad regional groups, operative temperature mapping provided greater environmental granularity, resolving four distinct spatial groups, including unique mid-latitude and coastal sub-populations. Specimen analysis revealed that cooler-climate groups exhibited smaller edge radii (higher margin dissection) than warmer-climate groups, with intermediate clusters displaying transitional values between the extreme ranges. These results demonstrate that operative temperature space offers an improved framework for identifying candidate morphological features associated with regional thermal environments, laying a foundation to test potential heat-transfer adaptations for engineering design.