Rwanda is located within the equatorial belt, its climate is strictly not of the equatorial rainy type. It has a modified humid climate including rainy forest and Savannah types. The central and eastern part of the country is generally of semi-arid type owing to its position in the rainy shadow of the western highlands.
The rainfall characteristics for Rwanda are known to exhibit large temporal and spatial variation due to varied topography and existence of large water bodies near the country. However, two rainy seasons are generally distinguishable, one centered around March – May and the other around October – December. Temporal variability of the rainfall in some occasions has resulted in extreme events such as the floods of 1997/98 El-Niño phenomena and frequent droughts that have far reaching socio-economic impacts to the country.
The warmest annual average temperatures are found in the eastern low lying (20 - 21°C) and Bugarama Valley (23 - 24°C), and cooler temperatures in higher elevations of the central plateau (17.5 - 19°C) and highlands (less than 17°C). Temperatures vary little throughout the year.
Rwanda experiences a bimodal pattern of rainfall, which is driven primarily by the progression of the Inter-Tropical Convergence Zone (ITCZ). The ITCZ follows the annual progression of the sun as it goes to the Northern Summer when the sun crosses the equator around March 21, and the Southern Summer around September 23 each year.
The maximum rainfall seasons occurs over March, April and May (MAM) and in September, October, November and December (SOND).