Northeastern India (east of 88o E and North of 21o N) has distinct precipitation and drainage patterns due to its unique location and orography. Empirical Orthogonal Function (EOF) analysis of southwesterly monsoon rainfall over India shows that seasonal rainfall patterns over the Northeastern region contrasts to that over the rest of the country(Neelima A. Sontakke). Between March and May in Northeast India, thunderstorms contribute about 20% of annual rainfall totals. During the months of June to September, southwesterly monsoons supply 70% of the annual precipitation. Another 8% of annual rainfall between October and November is associated with northeasterly monsoons. During the southwesterly monsoon season, frequent floods responsible for both human casualties and property damage occur as the powerful Brahmaputra River flows are constricted through the narrow Assam valley, fed by torrential rains and snowmelt from Himalayan ranges and laden with silt from actively eroding steep headwater slopes.

Seasonal variation of rainfall is the most distinguishing feature of the monsoonal regions of the world. A major portion of the annual rainfall over most of the Asian domain occurs during the summer monsoon period (June – September). The year-to-year variability in the monsoon rainfall occasionally leads to extreme situations of droughts and floods affecting the agricultural output and the national economy. Hence the variations in seasonal monsoon rainfall may be considered a measure to examine climate variability/ change over the Asian monsoon domain.