New gridded rainfall dataset over the Korean peninsula: Gap infilling, reconstruction, and validation

This study describes a new high-resolution (0.25 degrees x0.25 degrees latitude/longitude) gridded daily rainfall dataset (K-Hidra version 2020) developed from rainfall records of 389 gauge stations irregularly distributed across the Korean peninsula. The observational datasets are often composed of incomplete time series covering different temporal periods with numerous missing values, informing that infilling process is essential. Three supportive but separated evaluation frameworks, which have been paid less attention to, are explicitly addressed to identify the proper infilling model in the study area. After a gridded rainfall dataset is created with infilled dataset, it is validated by comparing the gridded products obtained by observations. Furthermore, K-Hidra is compared with other gridded rainfall estimates including Climate Prediction Center (CPC), Global Precipitation Climatology Project (GPCP), Asian Precipitation Highly-Resolved Observational Data Integration Towards Evaluation (APHRODITE), and Tropical Rainfall Measuring Missing (TRMM) Multi-satellite Precipitation Analysis (TMPA). Our results suggest that the elastic net model algorithm is the most effective in dealing with missing values in the study area. Results also demonstrate that the infilling process is vital to properly produce the reconstructed series although its effects substantially vary based on the size of the available data as well as the spatial and temporal distribution of the observed precipitation. Furthermore, K-Hidra reveals that the Korean peninsula have experienced significant changes in precipitation-related characteristics such as annual daily maximum precipitation and total annual dry days, likely leading to frequent hydrologic extremes. Lastly, K-Hidra is compared with other estimates, CPC has a small bias and high correlations with the new dataset while precipitation variabilities are acceptably represented by all other gridded estimates. From the results demonstrated in this study, when officially released, K-Hidra is expected to be useful for climate impact and rainfall variability analyses over the Korean peninsula.