Virtual Rain: A Unified Toolkit for High-Resolution Rainfall Simulation and Disaggregation

Abstract. Stochastic simulation models are essential for investigating hydrological processes and supporting water resource management. In this study, we introduce Virtual Rain, a two-step toolkit that first generates synthetic daily rainfall time series and then disaggregates them to a user-defined temporal resolution. The toolkit builds on the approaches recently proposed by some of the authors, ensuring a realistic representation of rainfall dynamics while preserving key statistical properties. The framework is implemented through a set of Python and R routines designed to facilitate practical application. In addition to providing observed rainfall time series and the scaling exponent 𝑛 (Intensity–Duration–Frequency slope), users can configure key modelling components, including the marginal distribution, autocorrelation structure, number of lags, and target temporal resolution. The routines generate both graphical and quantitative outputs, enabling direct comparison between observed and simulated series. Virtual Rain performance is evaluated through a real-world case study, demonstrating satisfactory accuracy and highlighting the robustness, flexibility, and transferability of the proposed toolbox. The toolkit is also available through an interactive web-based platform, facilitating its use by a broad range of users.