Besides the influence by its locations around the latitudes just north of the Tropic of Cancer, the climate of the state is governed by the relief of land and the rain bearing winds viz. the South-West Monsoon in summer and the North-East Monsoon and the Mediterranean winds in Winter. The eastern lowlands along the Indo-Burma border and the Western Assam Manipur border lowlands fall between the altitudes 30-100 m above m.s.l. and thus reigned by a tropical climate. The Manipur Valley at a height of 780-800 m. above m.s.l. has sub-tropical climate while the higher reaches of the mountains surrounding the valley have a temperate climate.
Referring to latitude of 24oN, Manipur valley at an average height of 790 m. above m.s.l. receives direct and diffuse solar insolation as follows.
Total radiationÂ Â Â = 290.36-780.86 cal/day/sq.m.
Visible radiation = 113.37-295.37 cal/day/sq.m.
The minimum values are recorded towards the winter months -Â a peak in June. Duration of bright sunshine has a variation of 3 hrs/day in July and 9 hrs/day in January. The surface level pressure ranges between 900 mb and 930 mb. Five seasons are distinct in the state viz; Summer (May-June), Rainy (Monsoon) (July-Sept), Autumn (Oct.-Nov), Cold winter (Dec.-Feb) and Spring (March-April). Since the onset, duration and amount of precipitation of the monsoon rain are erratic, this season classification may not hold good for a particular year and thus serves for general reference. The temperature ranges from 2oC to 36oC. Annual rainfall is sometimes as low as 975 mm and sometimes as high as 2,646 mm. Average relative humidity is between 36% and 100%. Rate of evaporation at the level of Imphal valley is between 1.8 mm in January and 4 mm in May.