Climatic factors include rainfall, temperature, humidity, frost and so on.
Rainfall data available in the Central State Farm, Aralam, which is just adjoining to the sanctuary area has been analysed.
Major source of moisture in the tract is in the form of rainfall. The total annual rainfall seldom falls below 4000 mm.
The maximum annual value for the nine years data available is 5052.60 mm and the minimum is 3745.50 mm.
In specialised localities, in the higher reaches (where there are no rain gauges), the rainfall even goes as high as over 6000mm.
Lion share (more than 70 %) of the rainfall is obtained during the southwest monsoon in June, July and August months.
The retreating monsoon though less pronounced, is an important source of moisture in October, November and December months, which constitutes 14% of the total. Summer rains vary widely and is not dependable.
It is a well-known fact that in the Peninsular India the vegetation type and growing period are determined by the extent of dry period rather than by the amount of rainfall.
The spread of rainy days across time (around the year) is a crucial determining factor in the plant growth. The dry period in the area varies between 3 to 4 months when the monthly rainfall is below 50 mm, and the number of rainy days varies from 100-120. Variation is observed in the quantity of rainfall as the altitude changes to higher levels.
The temperature at the foothills varies from 110c to 400c. The diurnal variations are moderate. As the altitude increases the variation is comparatively minimal which is between 80c and 250c. The hottest months are April and May. December to February is relatively cool.
At the foothills the humidity varies from 60 to 100%.
Regular winds lash the area during the southwest monsoon period. Strong winds of dry nature blow from September to April, causing dryness in the locality. With the result there is fire hazard, especially in the deciduous forests.
Locations where very high rainfall and peculiar soil conditions in the folds of the hills bring in specialised microclimatic situations leading to a peculiar habitat, which support relatively specialised vegetation. Such portions are found here and there on the higher reaches.