Comparative Analysis of Satellite and Gauge-Based Precipitation Data for Landslide Risk Assessment in Himalayas

The Himalayan region is prone to numerous landslides, primarily triggered by heavy precipitation. Most of these landslides occur from June to September, coinciding with the monsoon period. Therefore, monitoring rainfall intensity is vital for landslide risk assessment in the Himalayas. However, the sparse network of rain gauges in this region poses a significant challenge for climate extremes research. Satellite and Land Surface Model-derived precipitation products can help assess climate risks like landslides and floods without the need for installing rain gauges in remote locations. This study compares gauge-based and satellite-based precipitation products at 25 different locations using various statistical tools to evaluate their performance in landslide hazard assessment in the Himalayas. Based on statistical metrics, the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5) demonstrated the highest efficiency in reproducing spatiotemporal precipitation patterns at landslide-prone sites. The comparison involved metrics such as Root Mean Square Error (RMSE), Pearson Correlation Coefficient (CC), and Relative Bias (RB), along with rainfall frequency indicators and intensity comparisons. ERA5 emerged as the best-performing product, with RMSE ranging from 2.31 to 29.80, the highest CC, and the minimum RB at most sites. It successfully estimated 5761 days of very heavy rainy days (>20mm) compared to 5014 days recorded by rain gauges. Additionally, the correlation for rainfall intensity over a 30-day cumulative period was highest for ERA5 at most sites. The role of antecedent soil moisture in triggering of landslides cannot be ignored. However, in situ soil moisture data are rarely available in hazardous zones. The advanced remote sensing technology could provide useful soil moisture information. The study explores the use of GLDAS soil moisture product at the root zone depth along with ERA5 precipitation over a prolonged period to calculate thresholds for landslide initiation under different environmental conditions over the Indian Himalayas. The study reveals that certain combinations of Land Use Land Cover classes and soil types, especially on steeper slopes, are more susceptible to landslides, with landslides being triggered even at relatively low levels of soil moisture and precipitation.