Comparison of Relationship Between the Concentrations of Water Isotopes in Precipitation in the Cities of Tehran (Iran) and New Delhi (India) - Management of Natural Resources in a Changing Environment - page 35

result, the isotopic composition of precipitation in cold environments is more
depleted compared to warm environments. It means that isotope concentration
decreases with decreasing temperature as confirmed in Fig. 2 . This figure also
shows a good correlation between ʴ 18 O and air temperature in the New Delhi sta-
tion, while the corresponding correlation is relatively weak in the Tehran station.
Conclusions
In this study, time-series of oxygen and hydrogen stable isotope of the precipitation
water collected monthly from 1961 to 1987 in the stations of Tehran and New Delhi
were analyzed. The concentrations of water isotopes (ʴ 18 O, ʴD) vary spatially and
temporally. These variations result from isotopic fractionation processes at each
phase change of water during its atmospheric cycle. The changes in concentration
of these isotopes are used to trace the movement of water in hydrological and mete-
orological processes. The slopes of the least-squares fitting lines range from 6.48
(Tehran) to 7.02 (New Delhi) in all seasons. The obtained LMWLs for these stations
show significantly lower intercept and slope values than the GMWL. This result
shows good agreement with the results reported in some recent works (Kumar et al.
2010a ; Vodila et al. 2011 ). The source of the moisture in Tehran and New Delhi are
different, however the humidity is the same in the both cities. Therefore, the inter-
cepts of the itted LMWL are the same. By plotting ʴ 18 O values versus air tempera-
ture data of Tehran and New Delhi stations, a good correlation between ʴ 18 O and air
temperature in the New Delhi station ( R 2 = 0.987) was obtained, while a relatively
weak correlation was observed between ʴ 18 O and air temperature in the Tehran sta-
tion ( R 2 = 0.331). The obtained results also showed that the maximum and minimum
values of ʴ 18 O are obtained during winter and summer, respectively. A linear rela-
tionship exists between monthly isotope data and meteorological parameters at each
station. These results are consistent with the findings of Argiriou and Lykoudis
( 2006 ) in Greece.
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