In the tropics, temperatures are usually high throughout the year. Rainfall is, therefore , the mist important climatic factor that affects the biotic community of a terrestrial habitats. For example , a mean annual rainfall of 1800 mm results in a luxuriant rain forest, while an unreliable annual rainfall below 250 mm results in barren deserts. This is because water is the main constituent of living organisms, and so is essential for life.
Rainfall is especially important to fresh water aquatic habitats like ponds and streams. Lack of rainfall causes these water bodies to dry up, thereby killing most of the plants and animals living in them. Only a few organisms like the lung fish can survive such dry periods.
