Soils & Climate
The soils in the north of the Nouabalé-Ndoki National Park between the major rivers are reddish, sandy, ferric oxisols, over sandstones or sandstone- quartzites. The soils of much of the centre of the area are ferralitic, formed on the ancient alluvial deposits overlying the Bongoyo series, and towards the west, in the Sangha floodplain, are patches of poor red sandy soils of valleys, over sandstones. The swampy river valleys are underlain by very poor, sandy, leached hydromorphic mineral soils.
The climate of the Nouabalé-Ndoki National Park is transitional between the Congolo-Equatorial and sub-equatorial climatic zones. The average monthly temperatures and rainfall were recorded at Mbeli Bai within the National Park (8 years data); and at the NNNP HQ at Bomassa (4 years data, 30km west). The average annual rainfall at Mbeli Bai was 1273 mm, and at Bomassa 1499 mm. The rainy season has a bimodal distribution, with the main dry season from December to February, the main rainy season from August through November and a small rainy season in May; with between 100 and 120 rainy days per year. The average daily temperature is 26oC with little seasonal variation.