Multi-Scale Evaluation of Satellite Precipitation Products for Rainfall Estimation and Extreme Event Detection Across Tamil Nadu, India

Reliable precipitation data is important when conducting hydrological modeling, agriculture-related activities, drought monitoring, flood forecasting, and climate adaptation, especially in places where monsoonal influence is experienced. The rainfall regime in Tamil Nadu state, India, is characterized by the Southwest Monsoon, Northeast Monsoon, physiographic diversity, and the presence of cyclogenesis events. While SPPs offer the advantage of being consistent and having spatial coverage, there is a need for testing of their performance depending on climatic and topographic areas because performance differs across these environments. Three popular SPPs, CHIRPS, IMERG (Final Run), and MSWEP, were evaluated against daily observations from 37 synoptic stations across Tamil Nadu from 1998 to 2023. The performance of the SPPs was analyzed using continuous (RMSE, CC, PBIAS) and categorical (POD, FAR, CSI) measures. Seasonal rainfall characteristics and extreme rainfall detection skills were analyzed using Indian Meteorological Department rainfall intensity classifications. The results indicated that there were considerable differences between the products, with the best performance attributed to MSWEP having the minimum RMSE (11.2 mm), maximum correlation (0.30), minimum positive bias (10.0%), maximum POD (0.753), and maximum CSI (0.308). CHIRPS and IMERG underestimated the rainfall, especially in the Western Ghats region and cyclone-affected coast districts, leading to higher biases and false alarms. CHIRPS recorded RMSE = 11.5 mm, CC = 0.29, PBIAS = 25.3%, POD = 0.579, FAR = 0.681, and CSI = 0.257, while IMERG showed RMSE = 12.0 mm, CC = 0.27, PBIAS = 20.5%, POD = 0.662, FAR = 0.664, and CSI = 0.286, indicating that MSWEP consistently outperformed the other products in rainfall estimation and event detection. Seasonal analysis indicated better performance during the Northeast Monsoon, while MSWEP demonstrated uniform performance in both seasons. The results demonstrate the reliability of the MSWEP precipitation product in Tamil Nadu for hydrological and agricultural purposes.