Water Isotopes In The Hydrological Cycle

The heavy oxygen concentration (δ18O) and the heavy hydrogen concentration (δ2H) are the most important stable water isotopes in the hydrological cycle which are considered to be practical tracers to study the processes in water fluxes. Their abundance in water fluxes replicate features of physical phase change and controlling factors of variation with time and space. The fluctuation of precipitation isotopes in time and space in particular location reflect the complex atmospheric behavior affected water to be fractionated. Many observation programmes on stable isotopes in precipitation have been carried out since 1964 (Danssgard, 1964), and a variety of models are used to explain the observed precipitation isotopes (Gat, 1991; Yoshimura et

Partitioning or fractionation of isotopes of water (oxygen isotopes 16O and 18O, hydrogen isotopes 1H and 2H) occurs during condensation of vapour and evaporation of water in land surface and chemical transformations (e.g. vapor to liquid, liquid to solid). In the hydrological cycle, the repeated fractionation is particularly evident where repeated episodes of evaporation and condensation produce dramatic variations in the relative abundance of heavy (18O and 2H) and light isotopes (16O and 1H) in precipitation, surface water and ground water across the continents. During evaporation and condensation, the concentration of oxygen and hydrogen isotopes in water undergoes small changes. Therefore, water is naturally tagged with isotopic fingerprints, which vary according to the history of a particular body of water and its route through the hydrologic cycle. When water evaporates from the ocean, the heavier isotopes will condense first and fall as rain before the lighter ones. Thus, the further rainfalls from the coast, the fewer heavy isotopes it contains. At each stage of the hydrological cycle, there is a small change registered by a difference in the concentration of oxygen and hydrogen isotopes in water

The spatial and temporal fluctuation of water fluxes and their respective isotopes was discussed in the mesoscale of the Basin locations using the isotope enabled land surface simulation by IsoMATTRIP, the observed sample of stable water isotopes in precipitation, vapour, and surface and groundwater observation in the year 2014 rainy season. The variation of simulated annual average of mesoscale water budget, energy budget and isotopic fluxes in the year 2014 was compared in eight mesoscale locations of equal area (0.1250x0.1250) or 205.4 km2. The spin up run simulation of river discharge was reproduced for the year (1999-2009). The model simulation of river flow was evaluated with observational river discharge data from ministry of water resources of Ethiopia for 1999 to