On the sensitivity of Craig and Gordon model for the estimation of the isotopic composition of lake evaporates

Abstract

The effect of errors in the estimated isotopic composition of atmospheric moisture by δ(a) - δ(p) equilibrium assumption method on the isotopic ComPosition of lake evaporate (δ(E)) estimated using the Craig and Gordon linear resistance model has been studied. It has been found that the propagated error in estimated δ(E) increases with normalized relative humidity (h) but is less significant for h up to 0.5. The propagated error becomes unrealistic for h above 0.8. Since h is the major factor influencing the propagated error, an error in h would result in large uncertainty in the estimated δ(E). Simple analytical expressions for determining the propagated errors have been presented. The study also reveals that for the isotopic enrichment of a water body to continue, the difference between its isotopic composition and that of atmospheric air (Δ(la)) should be greater than the equilibrium enrichment factor (ε*). Using the relationship between Δ(la) and ε*, the maximum isotopic enrichment that a water body can achieve at different temperatures can be deduced.