Clarifying physiological adaptations is crucial to understand species distribution and predict vulnerability to changing climatic conditions. Considering energy and water constraints jointly is necessary because these facets are intertwined in ectotherms. The genus Vipera is a diversified group of Palearctic snakes with parapatric distributions and contrasted climatic affinities. These species are active thermoregulators relying on basking to maintain their body temperature. While some species such as V. berus and V. seoanei are adapted to cold and wet environments, other species have intermediate (temperate-oceanic) affinities (V. aspis), and some such as V. latastei and V. ammodytes inhabit warm and semi-arid climates. We studied physiological traits related to energy and water balance in these five species to better understand species' vulnerability to climate change. First, using open-flow respirometry we quantified standard metabolic rate (SMR) and evaporative water loss (TEWL) at three temperatures (15 degrees C, 25 degrees C and 33 degrees C). Cold-and wet-adapted species exhibited higher metabolic rates and evaporative water loss, reflecting adaptations to colder, wetter environments, while warm-and dry-adapted species showed lower rates. Second, we used these data to investigate their physiological responses to extreme climatic events (ECE). Simulated responses to summer heat spells revealed a major increase in energy expenditure and water loss rates across species. However, the effect was more prominent in cold-and wet-adapted species. This study underscores the physiological constraints that cold and wet-adapted species face during extreme climate events, providing insights into the vulnerabilities of ectotherms to ongoing environmental changes.