Summer monsoon rainfall variability over North East regions of India and its association with Eurasian snow, Atlantic Sea Surface temperature and Arctic Oscillation

Abstract

Nepal and Bangladesh, is influenced by local and remote forces. In terms of geographical size, NE-India constitutes of about 8% of India's total size. Its population is approximately 40 million, which represents around 3.1% of the total Indian population. This region has a predominantly humid sub-tropical climate with hot, humid summers, severe monsoons and mild winters. Along with the west coast of India, this region has some of the Indian sub-continent's last remaining rain forests, which supports diverse flora and fauna and several crop species. Geographically, two-thirds of the area is a hilly terrain interspersed with valleys and plains. The mean summer monsoon rainfall over the NE-Indian region is around 1400 mm making for huge water and hydropower potential. However, this region has been exhibiting a declining trend in the summer monsoon rainfall since the last 4-5 decades (see Fig. 3, Fig. 4a in Preethi et al. 2016). Hence, it becomes imperative to examine the possible drivers of this variability.Significance for long-term prediction of summer monsoon, considering its massive socio-economic impacts, have been widely attributed to the slowly varying boundary conditions such as sea surface temperature (SST) and snow cover (Shukla 1998). In general, rainfall distribution pattern over different regions of India is inhomogeneous due to influence of several local and remote factors. For instance, over the central Indian plain region, monsoon trough and the Himalayas along with local and external factors play a dominant role in its interannual rainfall variability. Likewise, the northwest region is influenced by the dry climates of the Thar Desert and the Western Himalayas. Apparently from the geographical features as described above, the rain producing mechanism of NE rainfall is a complex phenomenon and is largely dominated by an elevated orography of the Eastern Himalayas and large forests. The NE sector may be considered as a separate macro-region within the Indian Abstract This observational study during the 29-year period from 1979 to 2007 evaluates the potential role of Eurasian snow in modulating the North East-Indian Summer Monsoon Rainfall with a lead time of almost 6 months. This link is manifested by the changes in high-latitude atmospheric winter snow variability over Eurasia associated with Arctic Oscillation (AO). Excessive wintertime Eurasian snow leads to an anomalous cooling of the overlying atmosphere and is associated with the negative mode of AO, inducing a meridional wave-train descending over the tropical north Atlantic and is associated with cooling of this region. Once the cold anomalies are established over the tropical Atlantic, it persists up to the following summer leading to an anomalous zonal wave-train further inducing a descending branch over NE-India resulting in weak summer monsoon rainfall.

Correlations Between Extreme Atmospheric Hazards and Global Teleconnections: Implications for Multihazard Resilience

“…A link between the negative mode of the AO and reduced northeast Indian summer monsoon rainfall has recently been suggested by Prabhu, Oh, et al (2016). Higher than average wintertime Eurasian snowfall, associated with the negative AO, induces a descending meridional wave train over the tropical north Atlantic, causing cooling in this region.…”

Influence of climatic indices (AMO, PDO, and ENSO) and temperature on rainfall in the Northeast Region of India

“…The increasing heaviest rainfall events during the monsoon season are some extent associated with the Madden-Julian oscillation [21]. However, the wintertime Eurasian snow variability associated with Arctic Oscillation has been suggested to play a significant role in modulating monsoon rainfall variability [39]. In the inter-annual timescale, this study noted ENSO's influence on rainfall variability with low average cross-wavelet power.…”

“…The NE region's rainfall variability on the temporal scale is the integrated effects of natural climate modes [21,39,54,58,60]. The seasonal rainfall variability over this region is mainly due to the Indian monsoon system.…”

“…In the context of the attendant effect of oceanic indices on the rainfall variability over the NE region, Prokop et al [21] reported that the Madden-Julian Oscillation (MJO) plays a potential role in modulating extreme rainfall events during monsoon rainfall over the Meghalaya Hills of the NE region. In another study, Prabhu et al [39] reported a teleconnection between decreasing trend in summer monsoon rainfall of the NE region with Eurasian snow variability.…”

Determination of the Order of a Markov Chain for Daily Rainfall Data of North East India: "Application AIC criterion"

“…(2016). The average annual rainfall in North East India ranges from 2000-4000 mm with a maximum of 11000 mm in Cherrapunjee (Deka et al, 2011, Prabhu et al, 2016. The summer monsoon influence this region from June to September contributing more than 80% of the annual rainfall (see, Deka (2013).…”