BACKGROUND AND OBJECTIVES: Small and medium-sized lakes are numerically dominant in arid and semi-arid landscapes, yet their contributions to regional water balance and evaporation remain poorly constrained due to limited depth observations. The study objectives were to establish a regionally calibrated morphometric and hydrological framework that connects lake surface area with depth utilizing a logarithmic relationship derived for steppe environments in northern Kazakhstan. The framework enhances current methodologies by allowing for the concurrent estimation of lake depth, water volume, evaporation losses, and hydrological vulnerability in areas with limited data.METHODS: The model was calibrated using morphometric data from ۱۱۹ lakes in the Karaganda Region and applied to ۲۶۸ lakes with surface areas of ۱۰ square kilometers or less in the Akmola Region. The study incorporates the distribution of lake sizes, estimates of depth, and models of evaporation, while also presenting a Morphometric Evaporative Vulnerability Index that merges lake area, estimated depth, and regional evaporation intensity.FINDINGS: Lakes that measure between ۱ and ۱۰ square kilometers constitute about ۸۰ percent of total lake surface area and approximately ۷۹ to ۸۰ percent of the estimated water volume within the studied lake population. In contrast, lakes that are smaller than ۱ square kilometer account for approximately ۸ percent of surface area and contribute less than ۵ percent of of the total volume. More than ۸۰ percent of lakes have average depths below ۲ meters, with about ۴۱ percent concentrated between ۱ and ۱.۵ meters. The analyzed lakes collectively store about ۰.۹۷ cubic kilometers of water, whereas the larger lakes contain around ۱.۲۴ cubic kilometers. Annual evaporation losses total about ۵۶۷ million cubic meters, of which medium-sized lakes contribute about ۴۵۰ million cubic meters, while small and large lakes contribute about ۴۶ and ۷۱ million cubic meters, respectively. CONCLUSION: The results show that shallow and medium-sized lakes are predominant in evaporation fluxes and hydrological sensitivity, attributed to their extensive surface exposure and restricted depth. In contrast, larger lakes mainly serve as long-term reservoirs for water storage. The dominance of shallow lakes, comprising more than ۸۰ percent of the total number, highlights their role as early indicators of hydrological stress. The recommended framework delivers a scalable and data-efficient instrument for evaluating regional lakes, determining their vulnerability rankings, and integrating these findings into water resource management and climate adaptation strategies that utilize geographic information systems.
