Evaluation of NASA POWER Daily Rainfall Products Against Ground Observations in Sri Lanka

This study investigates the precision of NASA POWER’s daily rainfall estimations by comparing them with ground observations from 21 stations across Sri Lanka over a 30-year span. Four statistical assessments were conducted: coefficient of determination (R²), root mean square error (RMSE), mean bias error (MBE), and Willmott index of agreement (WI). R² values ranged from 0.3667 to 0.6117, with around 52.38% of stations displaying an R² of 0.5 or higher. RMSE fluctuated between 9 mm/day and 16 mm/day, while MBE ranged from − 3 to + 2 mm/day. WI values varied between 0.4273 and 0.6628. Overall, the results suggest a significant difference between NASA POWER’s predicted and actual observed rainfall values in Sri Lanka. NASA POWER predictions can be useful for forecasting rainfall in Sri Lanka, but only after applying appropriate error corrections.