Khatiwada et al. (2025) Multi-temporal flood mapping and dynamics in Nepal's Terai (2019–2024) using Sentinel-1 SAR and change-detection approaches

Identification

• Journal: Remote Sensing Applications Society and Environment
• Year: 2025
• Date: 2025-12-31
• Authors: Prabesh Khatiwada, Pragya Khatiwada, Him Lal Shrestha
• DOI: 10.1016/j.rsase.2025.101860

Research Groups

• UNIGIS Kathmandu, Kathmandu Forestry College, Nepal
• University of Salzburg, Austria
• Nepal Engineering College, Pokhara University, Nepal

Short Summary

This study conducted one of the first long-term, district-level flood mapping analyses in Nepal's Terai region (2019–2024) using Sentinel-1 SAR and CHIRPS rainfall data. It revealed frequent flooding in the southern region, with two extreme events exceeding 285 square kilometers, and established a strong positive correlation between 3-day cumulative rainfall and flood extent, identifying >130 millimeters as a threshold for major events.

Objective

• To conduct long-term, district-level flood mapping in Nepal's Terai region.
• To analyze flood dynamics from 2019 to 2024 in the flood-prone districts of Parsa, Bara, and Rautahat.
• To evaluate the relationship between short-term cumulative rainfall and flood extent.

Study Configuration

• Spatial Scale: Regional-scale, focusing on three flood-prone districts (Parsa, Bara, Rautahat) in Nepal's Terai region.
• Temporal Scale: Multi-temporal analysis from 2019 to 2024, producing monthly flood maps.

Methodology and Data

• Models used: Google Earth Engine (GEE) platform, change-detection approaches, CDAT, NDFI.
• Data sources: Multi-temporal Sentinel-1 Synthetic Aperture Radar (SAR) data, CHIRPS rainfall data.

Main Results

• The densely populated southern region of the study area is frequently affected by flooding.
• Two extreme flood events exceeded 285 square kilometers in extent.
• Flood maps from 2019 to 2024 showed both monthly and annual variations in flooding.
• 5.94 % of the study area was inundated 3–4 times during the study period.
• A strong positive correlation was observed between 3-day cumulative rainfall and the flooded area.
• A preliminary threshold of >130 millimeters of 3-day cumulative rainfall was identified for major flood events.

Contributions

• Provides one of the first long-term, district-level flood mapping studies in Nepal.
• Offers improved understanding of regional flood patterns in a data-scarce region.
• The findings are significant for developing data-driven mitigation measures and targeted flood risk management strategies.

Funding

No funding information was provided in the article text.

Citation

@article{Khatiwada2025Multitemporal,
  author = {Khatiwada, Prabesh and Khatiwada, Pragya and Shrestha, Him Lal},
  title = {Multi-temporal flood mapping and dynamics in Nepal's Terai (2019–2024) using Sentinel-1 SAR and change-detection approaches},
  journal = {Remote Sensing Applications Society and Environment},
  year = {2025},
  doi = {10.1016/j.rsase.2025.101860},
  url = {https://doi.org/10.1016/j.rsase.2025.101860}
}