Assam - Climate
Assam has four well defined seasons in a year namely, winter, summer, monsoon and spring. The state has tropical rainstorm atmosphere. It witnesses substantial precipitation and the summer temperature stays inside 38 degree Celsius. There is a distinct monsoon season in which a large part of the annual rainfall is concentrated. There are also two months of cyclonic activity preceding the monsoon, and rainfall at other times of the year as well. The topography and the warm and humid climate are conducive to plant and vegetation growth. Assam is home to 51 forest and sub-forest types, and the confluence of diverse patterns of vegetation.
Assam consists of two hill districts and twenty one plain districts. The climate of the hills is generally salubrious while that of the plains is comparatively warm in summer but cool in winter. Accordingly, the climate of Assam is characterised by alternate cool and warm periods with a highly humidity, especially from May to November. Between March and May at the time when precipitation in Northern India is at the minimum, Assam gets some amount of rainfall from the Norwesters which keep the temperature low in the season of spring. In the plains of Assam, the maximum temperature does not go beyond 90°F or 32°C and in winter the plains of Assam have a minimum temperature of about 8°C or about 47°F.
The climate of the plains and the sub-montane region becomes unpleasant,especially in the summer season. It happens to be so because of the extreme humidity which comes with the monsoon. In the plains of Assam, including the district of Cachar the temperatures in summer may be only about 32°C. But the humidity may be so high that one will perspire and feel very uneasy, especially during the period between two bouts of rainfall.
The humidity that is brought into Assam by the southwest monsoons, shower an average annual rainfall of 120 inches or more on the Brahmaputra valley and the surrounding region. The monsoons are Assam's lifeline; creating a bio-diversity that can compete with the equatorial rain-forests. Assam lying in the eastern Himalays is blessed with fertile soil and a moist tropical climate enabling it to have a treasure trove of biodiversity. This region‘s lowland and montane moist to wet tropical evergreen forests are considered to be the northernmost limit of true tropical rainforests in the world.
With the "Tropical Monsoon Rainforest Climate", Assam is temperate (summer max.at 35–39°C and winter min. at 5–8 °C) and experiences heavy rainfall and highhumidity. The climate is characterized by heavy monsoon downpours, which reducesummer temperatures, enable formation of foggy nights and mornings in winters. Spring (Mar–Apr) and autumn (Sept–Oct) are usually pleasant with moderate rainfalland temperature.
Though long term analysis is not picking up any trends in increase in extreme rainfall events but two extremely intense cloud bursts of unprecedented intensity - one in thewestern Meghalaya hills and Western Arunachal Pradesh in 2004 produced two devastating flash floods in the Goalpara and Sonitpur districts of Assam bordering Meghalaya and Arunachal respectively causing hundreds of deaths and enormous loss to the animals and agriculture.
Severe events occurredduring the monsoon season on June 14th, 2008 due to heavy rainfall on the hills of Arunachal Pradesh north of Lakhimpur District causing flash floods in the rivers of Ranganadi, Singara, Dikrong and Kakoi that killed at least 20 people and inundated more than 50 villages leading to displacement of more than 10,000 people. The other that occurred in the post monsoon season on October 26 affected a long strip of area of northern Assam valley adjoining foothills of Bhutan and Arunachal Pradesh causing flash flooding in four major rivers (all are tributaries of the river Brahmaputra) and a number of smaller rivers.
The southern part of Nagaon district in central Assam valley and adjoining parts of Karbi Anglong form a rain-shadow zone where annual rainfall is as low as 800-1200mm. Water scarcities are a potential constraint for the people living in this rainshadow zone and absence of effective irrigation systems or water harvesting practices adds to the vulnerability of the people. But what is of immediate concernis that rainfall in this zone is decreasing slowly. As a result water crisis might aggravate in this region in the coming years.
District level climate projections are available across Assam for the period 2021–2050. Temperatures continue to rise and may increase by 1.7-2.0°C over baseline. Only the western part of the State will experience slight decrease in rainfall, but the rest of Assam is projected to have increase in rainfall. There is likely to be increase in extreme rain fall event by 5 to 38% over the base line. Droughts weeks are going to rise, with Southern districts showing marginal reduction in drought weeks but the rest of the district show an increase by more than 75% wrt BL. As regards floods, they are going to rise by more than 25% in the southern parts of Assam.
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