Manas National Park and Barnadi Wildlife sanctuary are located at the foothills of the Bhutan Himalayas in Baksa, Chirang, and Udalguri districts of Assam. The geology consists of tract zone with sandy loam soil with granite and igneous as bedrocks. There is a well marked Bhabhar tract of rocky soil towards the boundary of the National Park which contains sandstone, limestone and shale, and have very little moisture retaining capacity. The Bhabhar tract generally remains drier. It is characterized by maximum relief, dissection, and drainage density within it.
List of rivers and nallahs inside Manas National Park:-
- Dhonbeel/Rupahi/Bangale hat-dhuwa/Pahumara
- Pota (Dry during the winter season)
- Hakuwa river
- Mora Manas
- Jiya pagla
- Lafasari nala
- Kanyasanti nala
- Artificial waterbodies.
It is moist tropical with an annual rainfall between 3000 mm to 4000 mm. The climate can be divided into four distinct seasons based on the variation in the rainfall, temperature, and winds. These are as follows:-
- Winter (December – February): Characterized by cool weather and fog. The temperature remains 20°C + 5°C. January is the coldest month. Average total rainfall is 114 mm with the relative humidity of 77% + 5.
- Pre-monsoon (March-May): It is a transitional period between relatively dry winter and hot summer and is characterized by a rapid rise in temperature. As the season advances, the amount and frequency of rainfall increases due to frequent thundershowers with hailstorms. Average total rainfall during the season is 518.70 mm. The season is marked progressively by a greater number of cloudy days. Average temperature and humidity in this season are 23°C + 5°C and 70% + 5 respectively.
- Monsoon (June-September): It is the characteristic major rainy season of the year. The average monthly rainfall is 2860 mm. The average temperature during this season is 27.17°C with an average diurnal range of over 6°C. The humidity increases to 82% + 5. August is the hottest month.
- Retreating monsoon (October-November): Towards the end of September, the monsoon weakens with an abrupt retreat followed by fair weather. With the advancing of the season, the temperature falls and moving mist and fog appears. The average temperature is 27°C + 2. The average monthly rainfall is 1400 mm and the rainy days become fewer. Relative humidity is 82% + 5.