The Hydrogen ( delta D) and Oxygen ( delta super(18)O) Isotopic Composition of Yemen's Rainwater

The isotope composition delta super(18)O and delta D of 214 rainwater samples collected from 2008 to 2010 from different geographic regions in Yemen was used to construct two regression lines considered as local meteoric water lines (LMWL). The two derived equations represent the first published LMWL's based on direct precipitation for any location in the country. One line was constructed for the highland region with slope 7.1 (n = 126). It differs slightly from the global slope 8.0 and was named as Yemen Highland's meteoric water line (YHMWL) defined by the equation: delta D = 7.1 x delta super(18)O + 8.2%. The other one was derived for the coastal regions named Coastal meteoric water line (Coastal MWL) for Yemen with slope 4.9 (n = 88) which is typical for evaporated water and defined by the equation: delta D = 4.9 x delta super(18) + 7.2%. The most important factors affecting the isotopic composition in Yemen's rainwater are the altitude, temperature, rainfall amount and the humidity. The rainfall events falling on the coastal plain are characterized by their content of the heavier isotope composition delta super(18)O and delta D. The slope of the line 4.9 indicates that these samples are strongly affected by evaporation due to the higher temperature and humidity in this region. In contrast, the rainwater in Yemen's highland is depleted in the heavier isotope composition and the samples are little affected by the evaporation due to the low temperature associated with the increase in the altitude and rainfall amount.