Nandi et al. (2026) Combined hydro-meteorological drought assessment of Ganga-Brahmaputra Basin: insights of the control of total water storage anomaly in drought occurrence

Identification

• Journal: Environmental Earth Sciences
• Year: 2026
• Date: 2026-03-11
• Authors: Subimal Nandi, Suvro Aon, Shoubhik Sen, Sujata Biswas
• DOI: 10.1007/s12665-026-12891-8

Research Groups

• Department of Civil Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah 711103, India

Short Summary

This study assesses hydro-meteorological drought in the Ganga-Brahmaputra Basin (GBB) using a combined drought index (CCDI) derived from GRACE-based Terrestrial Water Storage Anomaly (TWSA) and precipitation, revealing significant TWSA declines and identifying TWSA as the dominant driver of drought severity in the Upper Ganga and Yamuna-Chambal Basins.

Objective

• To explore the drought scenario of the Ganga-Brahmaputra Basin (GBB) using a combined drought index (CCDI) based on precipitation and GRACE-derived Terrestrial Water Storage Anomaly (TWSA).
• To quantify the relative contribution of TWSA and precipitation anomaly to drought occurrence in the GBB, including seasonal variations.
• To determine the spatially distributed drought propagation time (catchment response time) across the GBB using CCDI and Standardized Precipitation Index (SPI) time series.

Study Configuration

• Spatial Scale: Ganga-Brahmaputra Basin (GBB), including Upper Ganga Basin (UGB), Yamuna-Chambal Basin (YCB), Lower Ganga Basin (LGB), and Brahmaputra Basin (BB). Total area approximately 1,055,865 km². Data resolution is 0.25° x 0.25° for precipitation and GRACE-assimilated CLSM, with GRACE effective resolution of approximately 300 km.
• Temporal Scale: 2002 to 2022 (21 years).

Methodology and Data

• Models used: Combined Climatologic Deviation Index (CCDI), Standardized Precipitation Index (SPI), Lindeman-Merenda-Gold (LMG) method for relative importance analysis, cubic spline interpolation, linear regression, Karl Pearson correlation coefficient.
• Data sources: Gridded precipitation data from the India Meteorological Department (IMD); Terrestrial Water Storage Anomaly (TWSA) from GRACE/GRACE-FO monthly mass grids (RL06.1 M.MSCN v03 level 3 data) from Jet Propulsion Laboratory (JPL); GRACE-assimilated terrestrial water storage daily data from the Catchment Land Surface Model (CLSM) of the Global Land Data Assimilation System (GLDAS) v2.2 (used for gap filling).

Main Results

• Terrestrial Water Storage Anomaly (TWSA) shows a significant decline across the entire Ganga-Brahmaputra Basin (GBB) from 2002-2022. The Upper Ganga Basin (UGB) and Yamuna-Chambal Basin (YCB) experienced the sharpest declines at -2.622 cm/year and -2.116 cm/year, respectively, primarily due to groundwater extraction and climate variability.
• The Lower Ganga Basin (LGB) and Brahmaputra Basin (BB) showed slower TWSA declines of -0.840 cm/year and -1.065 cm/year, respectively.
• The Combined Climatologic Deviation Index (CCDI) revealed that UGB and YCB experienced fewer but more intense and prolonged droughts, while LGB and BB had more frequent, shorter, and less severe droughts.
• Relative importance analysis indicated that TWSA is the dominant contributor to CCDI and drought severity in UGB and YCB (over 90% contribution in upper regions), whereas both TWSA and precipitation anomaly (PA) significantly influence BB and parts of LGB.
• Seasonally, TWSA's contribution to CCDI is highest during the dry post-monsoon rabi (January-March) and pre-monsoon (April-June) seasons, and lowest during the monsoon (July-September).
• Drought propagation times (catchment response to precipitation deficit) vary: UGB and YCB show rapid responses (5–6 months), LGB has a slower response (6–7 months), and BB exhibits the shortest response (2–3 months) due to high rainfall.
• Detrending the CCDI time series to remove anthropogenic influences significantly improved its correlation with the Standardized Precipitation Index (SPI, increasing maximum correlation values from a range of -0.21 to 0.72 to 0.42 to 0.79.

Contributions

• Provides the first spatially distributed drought characteristics for the Ganga-Brahmaputra Basin (GBB) using the Combined Climatologic Deviation Index (CCDI).
• Quantifies the spatially and seasonally varying relative contributions of Terrestrial Water Storage Anomaly (TWSA) and precipitation anomaly (PA) to drought occurrence, identifying the dominant drivers in different sub-basins.
• Introduces a novel approach of detrending the CCDI time series to remove anthropogenic influences before analyzing drought propagation, leading to improved understanding of natural catchment responses.
• Offers crucial insights into hydrological drought dynamics and catchment response times, informing regional water resource management and mitigation strategies for a vital, agriculturally intensive basin.

Funding

No specific funding was received for this study.

Citation

@article{Nandi2026Combined,
  author = {Nandi, Subimal and Aon, Suvro and Sen, Shoubhik and Biswas, Sujata},
  title = {Combined hydro-meteorological drought assessment of Ganga-Brahmaputra Basin: insights of the control of total water storage anomaly in drought occurrence},
  journal = {Environmental Earth Sciences},
  year = {2026},
  doi = {10.1007/s12665-026-12891-8},
  url = {https://doi.org/10.1007/s12665-026-12891-8}
}