RainMerge: Open-Source Software for Unified Merging of Satellite and Gauge Precipitation Data

Rain gauges provide accurate point-scale precipitation measurements but are often sparsely distributed, particularly in data-scarce and complex-terrain regions. In contrast, satellite and reanalysis precipitation products offer continuous spatial coverage, yet they are affected by retrieval uncertainty and systematic bias. Reliable precipitation estimation therefore requires the integration of gauge observations with gridded satellite products. Existing merging approaches, however, are frequently limited in their ability to directly reconcile point-based gauge measurements with gridded satellite fields and to flexibly incorporate multiple datasets within a single, coherent workflow. We present RainMerge, an open-source, web-based framework that integrates gauge observations with multiple satellite precipitation products using pixel-level, uncertainty-aware merging. The platform automates data acquisition, preprocessing, uncertainty characterization, and merging within a unified computational environment. Through an intuitive graphical interface, RainMerge abstracts technical and geospatial complexity, enabling users without programming expertise to generate research-grade precipitation estimates. By bridging gauge-dependent and gauge-independent merging strategies while improving accessibility through user-oriented software design, RainMerge supports reproducible precipitation data fusion and broadens the practical use of multi-source precipitation merging in hydrological applications.