Arunachal’s climate varies with the elevation. The climate varies from hot and humid in the lower altitude to heavy rainfall in the Shivalik range. It become cold as one moves northwards to higher altitudes. Summers are not very hot, temperature ranges from 25oC to 35oC. Winters are cold, the temperature remains between 1oC to 15oC. Arunachal Pradesh observes heavy rainfall, average rainfall recorded is 3,300 cms.

Due to the great variety in topography, climatic conditions change within short distances. The southern part of the state has hot and humid sub-tropical climate. In the central areas, the climate is cooler, and in the inner or higher reaches, the climate is alpine. The rainfall too, though an almost year-round feature, is uneven. The best time to visit this state is October to April.

The climate is highly hot and humid at the lower altitudes and in the valleys covered by swampy dense forests particularly in the eastern section, while it becomes exceedingly cold in the higher altitudes.

The rainfall is amongst the heaviest in the country. The annual average rainfall in Arunachal Pradesh is more than 300 cm! The rainfall varies from 450 cm in the foothill areas to 80 cm in the upper reaches.

As can be expected, the vegetation of the whole of Arunachal varies gently in relation to the elevation of the different regions. It ranges from a wide belt of swampy rain forests along the foothills and the low lying areas to tropical and sub tropical. There's a great variety of plantation to be found. There are climbers, and an abundance of cane, bamboo and orchids. The lower altitudes are remarkable for their deciduous forests with patches of ever green tropical vegetation.

The forests of the state are its most important wealth. A huge revenue is earned from them each year. Over 22 million wood sleepers used by the Indian Railways in all the three gauges were supplied by the state.

Leasing of the tribal owned forest land to the forest department of the government is a unique system in the state. In the jungles of Arunachal, a large variety of medicinal plants are also available.

The natives utilize these plants for treatment and cure of a large number of diseases. Despite the fact that modern medicine is quite easily available now, the use of herbal medicines is still in vogue. Some of these herbal medicines are really quite effective.