Precipitation is partitioned at the earth's surface into surface runoff, infiltration into the ground (and subsequent groundwater recharge) and a return flux to the atmosphere by evapotranspiration. These processes modify the isotopic composition of precipitation as a result of the isotope fractionation which accompanies evaporative processes, and also as a result of selective utilization of rainfalls of different duration and intensities, and during different seasons, in runoff generation and groundwater recharge. The changes in the isotopic composition between the precipitation input and the output in the form of groundwaters and surface runoff results from processes on a wide range of temporal and spatial scales. Some take place during (or closely following) the rain on or above ground surface, e.g. on the vegetation canopy or on rock exposures. Others involve the soil moisture or shallow water reservoirs. Large lakes and the groundwater aquifers, at the other extreme, pool the inputs from large areas and over extended periods of time. Obviously for these different situations one needs to consider the isotope variability of the precipitation on quite different time scales, so that data from the Global Network of Isotopes in Precipitation (GNIP) must be reinforced by more detailed sampling campaigns. The difference in the isotopic composition between precipitation and the runoff or groundwater recharge is controlled by the interaction between the characteristics of the precipitation and nature of the terrain and in particular by the vegetation as of climatic change.
|Title of host publication||Isotope techniques in the study of environmental change. Proceedings of a symposium, Vienna, April 1997.|
|Publisher||International Atomic Energy Agency|
|Number of pages||12|
|State||Published - 1 Dec 1998|
ASJC Scopus subject areas
- Earth and Planetary Sciences (all)
- Environmental Science (all)