Reasons for 2022 deficient Indian summer monsoon rainfall over Gangetic Plain

Abstract

The variability of Indian summer monsoon rainfall (ISMR) has a socioeconomic impact on India. The profound relationship between ISMR and El Nino southern oscillation (ENSO) is getting weaker, due to which the impact of other climate modes has increased. Mid-latitude interaction with the monsoonal flow has increased in recent decades. Azores high, a high-pressure cell over the north Atlantic, modulates the mid-latitude wave pattern over the Eurasian region, consequently affecting Asian jet and Tibetan High. Accordingly, the repositioning of Tibetan High has shifted the ISMR band westward, causing above-normal rainfall in west and central India and below-normal rainfall in east and northeast India. The ISMR has significantly decreased over the Gangetic Plain, adversely affecting this region. This case study for the year 2022 summer monsoon has reflected one of the pieces of evidence of subdued rainfall over Gangetic Plain of India. The situation is unique because normal to above-normal rainfall was observed over the rest of the country. After analyzing various parameters, it is observed that the surface pressure anomaly over north India is against climatology, suggesting a rise in surface pressure and hence, weakening of the monsoon trough over the Gangetic Plain. This weak monsoon trough over the Gangetic Plain has reduced the monsoonal flow towards this region. Also, the strengthened Azore’s High impact through midlatitude waves reinforced the large deficit of ISMR over the Gangetic Plain during 2022.