Statistical Downscaling for Climate Change Studies: Comparing TCPG-GLM and Gradient-Boosted TCPG Models for Local-Scale Rainfall in Purwakarta
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Abstract
Accurate rainfall projections are vital for climate adaptation and water resource planning in tropical regions, where rainfall patterns are highly variable and zero-inflated. This study evaluates the performance of two statistical downscaling approaches based on the Tweedie Compound Poisson-Gamma (TCPG) distribution for monthly rainfall modeling in Purwakarta, Indonesia: the generalized linear model with Tweedie distribution (GLM-Tweedie) and the nonlinear Tweedie distribution boosting model (TDboost). Using observational rainfall data from five stations and predictor variables from three Earth System Models (BNU-ESM, MIROC-ESM, and MIROC-ESM-CHEM), model performance was assessed using root mean squared error of prediction (RMSEP) and Pearson correlation coefficient. The results show that TDboost generally outperformed GLM-Tweedie in terms of predictive accuracy and temporal consistency. At Cibukamanah station, TDboost achieved the lowest RMSEP under the MIROC-ESM-CHEM scenario (90.63 mm), while its highest correlation was obtained under the BNU-ESM scenario (r = 0.88). Similarly, at Cisomang station, TDboost under the MIROC-ESM-CHEM scenario achieved an RMSEP of 109.75 mm and a correlation of r = 0.78, indicating improved predictive performance compared with GLM-Tweedie. These findings suggest that distribution-aware boosting techniques can better capture the nonlinear and zero-inflated characteristics of tropical rainfall. The results also indicate that the best-performing ESM may depend on the evaluation metric used, with MIROC-ESM-CHEM providing lower prediction errors at some stations and BNU-ESM showing strong temporal correlation when combined with TDboost. Overall, this study highlights the importance of combining appropriate statistical downscaling models with suitable ESM predictors for improving local-scale rainfall prediction in complex tropical environments.
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References
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