Designing precipitation networks from altitudinal gradient patterns in global mountain basins

Altitudinal precipitation gradients (APGs) characterize the spatial distribution of precipitation in mountainous regions and constrain precipitation interpolation, with broad applications in meteorology, hydrology, ecology, and climate change research. They play a central role in shaping the ‘water tower’ function of mountains, yet their global distribution remains poorly characterized. Current precipitation datasets suffer from large uncertainties, and analyses often rely on spatial units that introduce scale-dependent biases. To overcome these limitations, we propose the mesoscale mountain basin unit (MMBU, 2000–20,000 km 2 ), which balances local topographic effects with reduced influence from large-scale circulation. Using eight widely applied precipitation datasets, APG patterns are examined across 5024 MMBUs, covering 63.9% of global mountain areas. This study classifies APG patterns into six types using parabolic fits to the precipitation–elevation relationship. Based on these patterns and the heterogeneity of non-zonal land cover, optimized precipitation observation networks are designed. Our analysis shows that more than 64,000 gauges would be needed to monitor mesoscale precipitation in mountain regions, with about 74% devoted to APG detection and the remainder to non-zonal variability. This observation strategy ensures broad spatial coverage by integrating elevation gradients with land surface heterogeneity. Mapping global APG patterns not only advances understanding of mountain water towers in a changing climate but also provides a framework for developing representative and efficient in situ precipitation networks worldwide.