Over the past two decades, the summer monsoon rainfall has shown decreasing trends over central India, with the Indo-Gangetic plains showing the most prominent changes. In particular, Bundelkhand, a subregion in the Gangetic plains, has experienced an increase in the frequency and severity of meteorological droughts.
We analyse long-term rainfall data revealing two types of droughts in Bundelkhand: Type-1 droughts that coincide with the large-scale Indian monsoon droughts, and Type-2 droughts, which are localised to Bundelkhand. Our focus in this work is on the spatio-temporal evolution of rainfall during the latter category of droughts.
A preliminary empirical orthogonal functional (EOF) analysis of ISMR clearly illustrates the dipole.
Bundelkhand experienced 12 Type-1 and 8 Type-2 droughts during 1901-2023. Type-1 droughts are in fact a subset of the large-scale ISMR droughts that have been studied extensively, with a majority of these years linked to El Niño. Type-2 droughts appear to coincide with weak to moderate La Niña like conditions in equatorial Pacific.
This dipole pattern of decreased JJAS rainfall over Bundelkhand and concurrently increased rainfall over western and southern India is the primary distinguishing factor between Type-1 and Type-2 droughts.
During a Type-2 drought, while central India receives near-normal rainfall, the western and southern parts of India experience above-normal rainfall. The average build up of rainfall deficit highlights a gradual buildup over Bundelkhand while the west India region shows above normal rainfall with a rapid increase over mid-July to end-August.
Type-2 drought conditions reveal similar trends in rainfall between Bundelkhand and western India until early-to-mid July, followed by a divergence that leads to a seasonal shortfall approximating 220 mm.
During early June rainfall is near-normal over most of India, and the first indications of a rainfall dipole emerge between late June and early July when Bundelkhand and parts of northeast India experience decreased rainfall. The distinct dipole structure with concurrent excess rainfall over western India is most pronounced during a six to eight-week period from mid-July to early September.
The magnitude of rainfall deficit in Bundelkhand peaks during early August and sustains until early September, signifying the subseasonal nature of the observed dipole pattern.
A midlatitude stationary Rossby wavetrain induces an anomalous anticyclone over western North Pacific between late July and mid-August, driving easterlies over the South China Sea into east-central India and reducing the regional moisture influx from monsoon northwesterlies. During September, the high-pressure region over Tibetan Plateau migrates further southward into central India, increasing subsidence.
Apart from rainfall deficit, meteorological droughts also impact other critical variables within the local hydrological cycle at the downstream end. Type-2 droughts exhibit localised deficit in soil moisture confined to Bundelkhand, and the enhanced soil stress owing to reduced rain may have a role to play in the much-reported depletion of groundwater storage in northwest India and Bundelkhand in particular.
Further investigations into local groundwater flow, recharge, and evapotranspiration patterns are crucial. Drought mitigation strategies for Bundelkhand must be informed by the distinct vulnerabilities associated with both Type-1 and Type-2 droughts.