Sarat et al. (2026) The subseasonal evolution of Indian rainfall dipole and its local impact in recent decades

Identification

• Journal: Climate Dynamics
• Year: 2026
• Date: 2026-01-13
• Authors: C. Sarat, Vuruputur Venugopal, Sekhar Muddu
• DOI: 10.1007/s00382-025-07955-7

Research Groups

• Interdisciplinary Centre for Water Research, Indian Institute of Science, Bangalore, India
• Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India
• Divecha Centre for Climate Change, Indian Institute of Science, Bangalore, India
• Department of Civil Engineering, Indian Institute of Science, Bangalore, India

Short Summary

This study categorizes Indian summer monsoon droughts into two types (widespread Type-1 and localized Type-2 in Bundelkhand) and investigates the subseasonal evolution and atmospheric drivers of the localized Type-2 droughts, revealing a distinct rainfall dipole pattern and its significant hydrological impacts.

Objective

• To analyze the interannual and subseasonal evolution of the Indian Summer Monsoon Rainfall (ISMR) dipole, particularly focusing on localized (Type-2) droughts in the Bundelkhand region.
• To perform a diagnostic analysis of upper-level atmospheric circulation to identify potential local and remote drivers of the observed subseasonal variability leading to the rainfall dipole pattern.
• To assess the downstream hydrological impacts, specifically on soil moisture and groundwater, in the Bundelkhand region during these drought events.

Study Configuration

• Spatial Scale: India, with a specific focus on Bundelkhand (approximately 22–27° N, 78–83° E), West India (17–25° N, 69–78° E), Indo-Gangetic Plains, central India, northeast India, peninsular India, Tibetan Plateau, western North Pacific, and South China Sea.
• Temporal Scale: Long-term analysis of rainfall from 1901 to 2023 (June-September, JJAS). Soil moisture data from 2003 to 2023. Groundwater data from 1995 to 2019. Subseasonal evolution within the JJAS period is a key focus.

Methodology and Data

• Models used: Global Land Data Assimilation System (GLDAS) Catchment Land Surface Model (CLSM) for soil moisture.
• Data sources:
  • Observed Rainfall: Indian Meteorological Department (IMD) daily gridded rainfall at 1° resolution (1901–2023).
  • All India Summer Monsoon Rainfall (AISMR): Indian Institute of Tropical Meteorology (IITM) homogeneous rainfall record from 306 rain gauges.
  • Atmospheric Reanalysis: ERA5 (European Centre for Medium-Range Weather Forecasts) daily reanalysis fields (zonal wind, meridional wind, vertical pressure velocity, Geopotential Height, vorticity, vertically integrated moisture divergence) at 0.25° resolution (1970–2023).
  • Soil Moisture: GLDAS Catchment Land Surface Model (CLSM) daily profile in kg/m² at 0.25° resolution (2003–2023).
  • Groundwater: Depth to groundwater level (DGWL) data from Central Groundwater Board (CGWB) wells in Bundelkhand (1995–2019).
  • Methodology: Daily and j-day anomaly calculations, drought classification based on IMD criteria (percentage deviation from long-term mean), Empirical Orthogonal Function (EOF) analysis, composite analysis, and diagnostic analysis of atmospheric circulation.

Main Results

• Drought Categorization: Two distinct drought types were identified in Bundelkhand: Type-1 (coinciding with large-scale Indian monsoon droughts) and Type-2 (localized to Bundelkhand).
• Rainfall Dipole: Type-2 droughts exhibit a prominent subseasonal rainfall dipole, characterized by decreased rainfall over Bundelkhand (east-central India) and concurrently increased rainfall over western and southern India. This dipole is most pronounced from mid-July to early September.
• Subseasonal Evolution: In Type-2 droughts, rainfall deficit initially develops over northeast India and Bundelkhand around mid-July. The deficit (excess) peaks in Bundelkhand (western and peninsular India) during early August and persists until early September. The end-of-season rainfall deficit in Bundelkhand reaches approximately 300 mm (30–40% of seasonal accumulation) for both drought types.
• Atmospheric Circulation (Type-2):
  • July-August: A midlatitude stationary Rossby wave induces an anomalous anticyclone over the western North Pacific, driving easterlies into east-central India, reducing regional moisture influx and causing subsidence. Simultaneously, it induces an anomalous cyclonic circulation over northwest India and Pakistan, enhancing moisture convergence from the Arabian Sea and increasing convection over western India.
  • Late August-Early September: The anticyclonic cell over the Tibetan Plateau migrates southward into central India, strengthening subsidence. This leads to a distinct east-west dipole in vorticity, driving the observed rainfall asymmetry.
  • Vertical Circulation: Anomalous descending motion (subsidence) is observed in east-central India (75–100° E) and ascending motion (convection) to the west of 75° E (western India) during early August.
• Hydrological Impacts:
  • Soil Moisture: Type-1 droughts result in widespread soil moisture deficit across central and peninsular India. Type-2 droughts show a more localized soil moisture deficit confined to Bundelkhand, while western and peninsular India experience increased soil moisture.
  • Groundwater: Frequent meteorological droughts (both Type-1 and Type-2) contribute to sustained groundwater depletion in Bundelkhand. Post-monsoon average depth to groundwater level in northern Bundelkhand decreased from 5 m before 2005 to almost 10 m by the end of 2008, compounded by human intervention.

Contributions

• Provides the first detailed subseasonal analysis of the Indian Summer Monsoon Rainfall (ISMR) dipole, particularly for localized (Type-2) droughts, through a comprehensive composite analysis across years.
• Identifies distinct atmospheric circulation mechanisms, including the role of midlatitude Rossby waves, the western North Pacific anticyclone, and the southward migration of the Tibetan Plateau anticyclone, in driving the subseasonal evolution of Type-2 drought patterns, differentiating them from canonical ENSO-driven droughts.
• Offers a holistic framework by analyzing the downstream hydrological impacts (soil moisture and groundwater) of both drought types, highlighting the localized and persistent soil moisture deficit in Bundelkhand and its contribution to groundwater depletion.
• Emphasizes the critical implications for drought management strategies in Bundelkhand and the Indo-Gangetic Plains, advocating for consideration of these distinct drought categories.

Funding

• Prime Minister’s Research Fellowship (PMRF), Government of India (C. Sarat)
• Science and Engineering Research Board (SERB), Department of Science and Technology, Govt. of India (grant number CRG/2021/002441) (V. Venugopal)
• Ministry of Earth Sciences (MoES), Govt. of India (IITM/MM-III/2024/IND-10, as part of Monsoon Mission Phase III) (V. Venugopal)

Citation

@article{Sarat2026subseasonal,
  author = {Sarat, C. and Venugopal, Vuruputur and Muddu, Sekhar},
  title = {The subseasonal evolution of Indian rainfall dipole and its local impact in recent decades},
  journal = {Climate Dynamics},
  year = {2026},
  doi = {10.1007/s00382-025-07955-7},
  url = {https://doi.org/10.1007/s00382-025-07955-7}
}