Improving satellite-based global rainfall erosivity estimates through merging with gauge data

Rainfall erosivity is a key factor that influences soil erosion by water. Rain-gauge measurements are commonly used to estimate rainfall erosivity. However, long-term gauge records with sub-hourly resolutions are lacking in large parts of the world. Satellite observations provide spatially continuous estimates of rainfall, but they are subject to biases that affect estimates of rainfall erosivity. We employed a novel approach to map global rainfall erosivity based on a high-temporal-resolution (30-min), long-term (2001-2020) satellite-based precipitation product-the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (GPM-IMERG)-and mean annual rainfall erosivity from the Global Rainfall Erosivity Database (GloREDa) stations (n = 3286). We used a residual-based merging scheme to integrate GPM-IMERG-based rainfall erosivity with GloREDa using Geographically Weighted Regression (GWR). The accuracy of the GWR-based merging scheme was evaluated with a 10-fold cross-validation against GloREDa stations. Based on GPM-IMERG-only, the global mean annual rainfall erosivity was estimated to be 1173 MJ mm ha-1 h-1 yr-1 with a standard deviation of 1736 MJ mm ha-1 h-1 yr -1. The mean value estimated via GPM-IMERG merged with GloREDa was 2020 MJ mm ha-1 h-1 yr-1 with a standard deviation of 3415 MJ mm ha-1 h-1 yr -1. Overall, GPM-IMERG-only estimates underestimated rainfall erosivity. The underestimations were greatest in areas of high rainfall erosivity. The accuracy of rainfall erosivity estimates from GPM-IMERG merged with GloREDa substantially improved (Nash-Sutcliffe efficiency = 0.83, percent bias =-2.4%, and root mean square error = 1122 MJ mm ha-1 h-1 yr-1) compared to estimates by GPM-IMERG-only (Nash-Sutcliffe efficiency = 0.51, percent bias = 27.8%, and root mean square error = 1730 MJ mm ha-1 h-1 yr -1). Improving satellite-based global rainfall erosivity estimates through integrating with gauge data is relevant as it can contribute to enhancing soil erosion modeling and, in turn, support land degradation neutrality programs.

Automated summary

Rainfall erosivity is a crucial factor in soil erosion caused by water, and rain-gauge measurements are commonly used to estimate it. However, long-term and sub-hourly resolution gauge records are lacking in many areas. Satellite observations provide continuous estimates of rainfall but may be biased in estimating rainfall erosivity. In this study, we combined high-temporal-resolution satellite data with annual rainfall erosivity observations to improve the accuracy of global rainfall erosivity estimates.