The hydrology of humid tropical regions such as South-east Asia is strongly affected by climatic phenomena having important periodicities ranging from hours to decades. This papers describes how temporal climatic features influence canopy hydrology, runoff processes and water quality in the humid tropics. Emphasis is given to hydrologcal studies from South-east Asia, a region impacted by cyclonic, convective and stratiform rainfall, strong diurnal cycles in net radiation, and rainfall cycles resulting from monsoons and the El Nino - Southern Oscillation. Understanding how natural climate cycles affect hydrology is a necessary precursor to understanding how man-made climatic changes might influence tropical water resources.