Downscaling the GPM-based satellite precipitation retrievals using gradient boosting decision tree approach over Mainland China

Abstract

Remote sensing brings unprecedented opportunities to estimate precipitation at regional, continental, and even global scales. Nevertheless, the spatial resolutions of current mainstream satellite precipitation estimates are still too coarse to be directly used in the hydrological and meteorological applications over the medium and small scales. The spatio-temporal distribution of precipitation is often affected by various land surface factors, such as geographical location, vegetational cover, topographic characteristics, and ground temperature. Based on the relationship between precipitation and multi-geospatial factors, this study proposed a new spatial downscaling approach named as gradient boosting decision tree (GBDT) to downscale the annual satellite precipitation estimates of Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) from 0.1° to 0.01° gridded resolution over Mainland China from 2015 to 2018. As for the preprocessing of downscaling algorithm, the entire study area of Mainland China was separated into four different climate regions due to the spatial discrepancy of the relationship between precipitation and geospatial factors. To validate the effectiveness of GBDT approach, we compared it with other two types of downscaling methods based on random forests (RF) and support vector machine (SVM), respectively. Our evaluation results show that the geographical location (including both latitude and longitude) seems to be relatively more important and stable for GBDT modelling than other land surface factors across the four climate regions in Mainland China. In terms of large spatial scales, the GBDT and RF algorithms generally are superior to SVM for downscaling the IMERG precipitation, as SVM reduced the considerable accuracy of the downscaled results. Last but not least, GBDT exhibits more robust features in downscaling the satellite precipitation retrievals than RF over complex terrains, where the amount of precipitation has strong spatial heterogeneity.