Podkowa et al. (2026) SMAP Satellite Microwave Radiometry to Monitor River Flow and Lake Level in the Lower Mekong Basin

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Identification

• Journal: Earth and Space Science
• Year: 2026
• Date: 2026-01-01
• Authors: Anna Podkowa, S. V. Nghiem, Zsófia Kugler, G. R. Brakenridge
• DOI: 10.1029/2025ea004436

Research Groups

NASA (Soil Moisture Active Passive Mission - SMAP)

Short Summary

This paper demonstrates the capability of NASA's SMAP satellite passive microwave radiometry (PMR) for monitoring river stage, discharge, and lake levels in the Lower Mekong Basin, showing high correlation with in situ data across diverse river widths and effectively capturing seasonal, interannual, and dam-induced hydrological changes.

Objective

• To demonstrate and validate the capability of NASA SMAP satellite passive microwave radiometry (PMR) for measurements of river stage, river discharge, and lake level using in situ gauging data in the Lower Mekong Basin.

Study Configuration

• Spatial Scale: Lower Mekong Basin (LMB), including five river gauging locations (e.g., Mekong River, Songkhram River) and Tonle Sap Lake. River widths ranged from 42 meters to 1735 meters.
• Temporal Scale: Seasonal and interannual patterns, with observations on a daily to nearly daily basis over multiple decades when synergized with other satellite data. Analysis covered periods before and after dam operations (Xiaowan and Nuozhadu) and included the 2015 exceptional drought year.

Methodology and Data

• Models used: SMAP Passive Microwave Radiometry (PMR) method.
• Data sources: NASA Soil Moisture Active Passive Mission (SMAP) satellite passive microwave radiometry (PMR) observations, in situ gauging data, satellite Ka-band PMR, and Soil Moisture and Ocean Salinity (SMOS) data.

Main Results

• The SMAP PMR method was consistently validated with forward-split, backward-split, and full-record approaches, showing strong agreement with in situ gauging data across all selected locations.
• High correlation values (≥0.9) and Nash-Sutcliffe Efficiencies (>0.8) were achieved for both narrow (42-meter width) and wide (1735-meter width) rivers.
• SMAP PMR observations accurately captured seasonal and interannual patterns of river change, reflecting flood and drought conditions.
• Synergy with satellite Ka-band PMR and SMOS data over multiple decades enabled the identification of flood and drought events and abrupt changes in river flows linked to the operation of the Xiaowan and Nuozhadu dams on the Lancang (upper Mekong) River.
• Post-dam operation, the wet-season flow stage in the lower Mekong River no longer reached the 2.33-year flood stage, and dry-season water levels dropped below the lowest stage recorded during the 2015 drought.

Contributions

• First demonstration and validation of SMAP PMR for global river stage, discharge, and lake level monitoring, including its effectiveness across a wide range of river widths.
• Established the capability of satellite PMR to detect significant hydrological changes, such as those induced by large dam operations and extreme drought events, over multi-decadal periods.
• Provides a robust, globally applicable method for daily to nearly daily monitoring of river and lake levels, enhancing global water resource management and flood/drought monitoring.

Funding

NASA

Citation

@article{Podkowa2026SMAP,
  author = {Podkowa, Anna and Nghiem, S. V. and Kugler, Zsófia and Brakenridge, G. R.},
  title = {SMAP Satellite Microwave Radiometry to Monitor River Flow and Lake Level in the Lower Mekong Basin},
  journal = {Earth and Space Science},
  year = {2026},
  doi = {10.1029/2025ea004436},
  url = {https://doi.org/10.1029/2025ea004436}
}