Chapter 3 - Isotopic Variations in Precipitation

Abstract

This chapter provides an overview of precipitation. It is probably the most important source of water to catchment basins. The stable isotopic composition of precipitation has been shown to be highly variable on temporal scales from intra-storm to years and, depending on type and mode of precipitation, on geographic scales as little as kilometers and less. Any isotopic study at the catchment basin scale must start with an understanding of the formation of precipitation, and the specific temporal and geographic variations in the stable isotopic ratios of precipitation. The stable isotopic composition of precipitation is a function of various parameters, most of which indeed act at the catchment scale. Understanding these parameters and their effect on the stable isotopic ratios of precipitation yields information concerning the hydrology of catchments. Precipitation is of major interest in the hydrologic cycle as it is the ultimate source of water to catchments. The terrestrial portion of the hydrologic cycle to the hydrologist begins when precipitation reaches the ground. Therefore, an understanding of the formation of precipitation, and knowledge of temporal and geographic variations in the amount and mode of precipitation are important to hydrologists and critical for basin-widewater balance studies.