Publication Name

Extreme rainfall events – Brahmaputra

Differences in highest rainfall baseline 1961–1990




-50 -25 -5 0 5 25 50

Differences in rainfall intensity baseline 1961–1990



Millimetres per day

-5.0 -2.5 -0.5 0 0.5 2.5 5.0

Rainfall distribution varies considerably between the southern and northern parts of the basin. The lower Brahmaputra basin receives approximately 2,216 mm of rain annually, which is over three times more than the upper basin. There are approximately 164 rainy days a year in the upper Brahmaputra and 214 in the lower Brahmaputra basin. No specific trend of change in the amount of rainfall has been observed between the baseline period of 1951–1980 and 1981–2007. Extreme rainfall appears to be decreasing in the north, but increasing over eastern portions of the basin. Rainfall intensity (mm/day) has increased slightly over eastern portions of the basin. Temperature Over the past decades and across the basin, temperatures are changing over time and showing

mixed trends across the seasons and in different areas of the basin. Overall, increasing trends are seen in average winter minimum temperatures, as well as in night-time temperatures. The average maximum temperature in the Brahmaputra basin is 19.6°C in the summer and approximately 9.2°C in the winter. The average minimum temperature is –0.3 °C in winter and 18.3°C in summer (these figures are seasonal averages for June, July, August and September for summer and December, January and February for winter). Minimum temperatures are showing an increasing trend: there has been a significant rise of 0.5°C in average minimum winter temperature across the basin. Within the pre-monsoon and post- monsoon, the rise is 0.3°C and 0.4°C, respectively. The temperature in the summer (monsoon) has not changed. Average summer maximums are showing

a slight increase, but it is not significant. However, night-time temperature shows a highly significant warming trend for winter as well as summer. Extreme high temperatures (highest maximum temperature) are increasing over the northern parts of the basin (the Tibetan plateau), but decreasing east and southwards. Extreme minimum temperatures are decreasing (getting colder) in the centre of the basin.


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