Standardized Precipitation Index (SPI) Computation Program

This MATLAB-based program computes the Standardized Precipitation Index (SPI), primarily used for drought classification assessment. The implementation handles precipitation data processing through multiple stages: data reading from various formats (Excel, CSV, text files), data storage management, statistical processing, analytical computations, and visualization output. The SPI algorithm works by fitting long-term precipitation data to a gamma probability distribution, then transforming it to a standard normal distribution to calculate standardized deviations. The core computation involves determining cumulative precipitation probabilities and converting them to z-scores representing drought intensity levels. The program includes multiple analytical tools for data interpretation, featuring functions for temporal analysis, threshold detection, and trend visualization. Comprehensive documentation and technical support are provided, including detailed comments on key functions like data preprocessing, distribution fitting, and SPI calculation algorithms to facilitate user adaptation and extension.