Climate, Rainfall and Temperature :

Assam at present 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 90oF.or 32oC and in winter the plains of Assam have a minimum temperature of about 8oC or about 47oF.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 32oC. But the humidity may be so high that one will perspire and feel very uneasy, especially during the period between two bouts of rainfall.


 

From the climatic point of view the year in Assam can broadly be divided in two, the cold season and the rainy season. However,there are two other short seasons namely spring and autumn representing the transition between cold and rainy seasons and that between rainy and cold seasons respectively.


 

From the middle of November to the middle of February the cold season prevails with the sky becoming clear and temperature going down below 15oC. Fogs also appear during these months, especially in the morning and evening but they disappear during the daytime. From March temperature begins to rise,dust,storms begin ti blow in western Assam and occasional Northwesters visit with thunderstroms. The showers of this period prevent the temperatures from rising and they settle down the unwanted dusts which appear in the air. Besides, they also help to make the vegetation green after the dry winter. After the short spring the south west monsoon bursts in the third week of June and rains continue to pour with short spells of drought. The atmosphere there becomes sultry and temperature stands at 30oC to 35o C. Towards late September,the rains peter out and temperature also decreases and the short autumn sets in,while the sky begins to become clear mists appear in the horizon. With the farther fall of temperature, winter sets in from late November.

There is a slight variation of climate from region to region within the State. For instance, the climate of the region covering Kamrup, Nalbari and Barpeta in west-central Assam is characterised by plentiful rains and foggy winter. The cold season in this region is from December to February and this is followed by the sand-storms and thunderstorms from March to May. The rainy season,

as in rest of Assam begins in late June and continues upto late September. October and November constitute the post-monsoon period. In western Assam comprising the districts of Goalpara, Bongaigaon, Kokrajhar and Dhubri,the climate is intermediate between that of the North Bengal Plains and the west-central Assam Valley. In this region,the day temperatures in April and May are nearly the same as in the monsoon months. The climate of the Barak Valley districts is characterised by abundant rainfall, moderate temperatures and high humidity. The year may be divided into four seasons and the cold season is identical with Goalpara and Kamrup. The climate of the east central Assam comprising Darrang, Sonitpur, Marigaon and Nagaon is characterised by the absence of a dry hot summer season,the highest temperature being experienced during the period of south west monsoon along with abundant rains and a humid atmosphere throughout the year. The climate of the eastern Assam districts (Golaghat, Jorhat, Sibsagar, Tinsukia ,Dibrugarh, Dhemaji and Lakhimpur)is somewhat identical to Darrang and Nagaon with temperature remaining slightly lower than in the latter.


 

Humidity : In most of the plain districts of Assam the air is highly humid throughout the year. In Kamrup district,during the months of January to April relative humidities are comparatively less being only 50 to 60%.The same condition holds good in case of Goalpara district where humidities are less,especially in the afternoon,when they are between 50 to 65 per cent. During February and March in the district of Cachar,the air is comparatively less humid,the afternoon humidities being less than 60 per cent. In Darrang too, the air is highly humid throughout the year,except during the period February to April when the relative humidity is comparatively less,particularly in the afternoon(less than 70 per cent).But in the Lakhimpur and Dhemaji districts and in Majuli sub-division of Jorhat district,the air is very humid throughout the year,the relative humidity being usually over 70 %.In Nagaon district, during the period February to April relative humidity is comparatively low,especially in the afternoon when it stands between 55% to 65%.In Golaghat, Jorhat and Sibsagar too, the atmosphere is highly humid throughout the year. The two hills districts of Assam,namely Karbi Anglong and North Cachar Hills, have also almost similar humidity with the rest of Assam particularly so during the period of south west monsoon season when the relative humidities are above 80%.The period from February to April is comparatively drier here with the relative humidities are in the afternoon between 50 to 60 per cent.


 

Rainfall-Assam receives typical monsoon rains. The south-west monsoon rains starts from the third week of June and they continue up to the middle of September. The State receives during this period about 180 cm of rainfall on the average. This constitutes about 80% of the average rainfall of the State while


 

the remaining 20% come in the form of occasional rains in January (as a result of the extension of the westerlies that come to the north-western India causing rainfall in Panjab, Haryana and western Uttar Pradesh and snowfall in Jammu and Kashmir, Himachal and the Himalayan region and in March-April (nor'westers or Bordoichila).There is however . religion variation in the rainfall pattern. It is found that as the Maghalaya .Plateau stands on the way of the main branch of the rain -bearing south-west monsoon winds .the southern portion of the Brahmaputra Plains skirting the Plateau fall in the rainshadow zone . Hence the south-eastern part of Kamrup district from Guwahati eastward. Southern part of Nagaon district .northern part of Hamren sub-division and the eastern foothills of Karbi -Rengma hills receive less rainfall than the other parts of the Brahmaputra Plains. In fact, the Lanka-Lumding receives hardly 100 cm of average annual rainfall. Similarly, the Diphu-Nambar region also receives a small quantity of rain. In other parts of the Bhrahmaputra Plains, rainfall increases as one goes to the east or north or west. The heaviest rainfall exceeding 200 cm is received in Tinsukia, Dibrugarh, Dhemaji and Lakhimpur districts and along the Himalayan foothill region. The average annual rainfall is around 200cm all over the middle part of the Brahmaputra Valley from the east to the west. While the western part Of Karbi Anglong receives 200cm of average annual rainfall. North Cachar Hills and the Barak plains receive more than 200cm.

The tables below show the monthly data of rainfall, temperature and relative humidity of different stations of Assam.

 

Source-Meteorological Centre,Calcutta.A.P.-Air Port

 

Source – Meteorological Centre,Calcutta.

 

Source- Meteorological centre,Guwahati N.A.-Not Available

 

Source-Meteorological Centre,Guwahati.* Annual normal rainfall N.A.-Not Available A.P.-Air Port

 

 

 

Source: Meteorological Centre,Calcutta,N.A-Not Available

 

NB: not reported

(1)-Total of less than 10 days reports 00-Nil tr-rainfall 0.1 to 0.4 mm

Source:-Directorate of Economics & Statistics,Assam;Statistical Hand Book,Assam,1987.

 

Source-Statistical Hand Book,Assam,1991,p-28-31

 

Source-Statistical Hand Book,Assam,1993,p-50-53.

 

Source:Meteorological Centre,Guwahati.

 

Source: Statistical Hand Book,Assam,1982,p-54-5.

 

Source-Statistical Hand Book,Assam,1993,p-46-7.

 

 

Source : Meteorological Centre. Guwahati

 

 

Source -Staistical hand Book,Assam,1982,p-56 and 1987,p-44