Abstract:
The study evaluates the water vapor isotopic compositions and its controls with special reference
to Indian Summer Monsoon (ISM) season at Roorkee, India. Precipitation is usually a discrete
event spatially and temporally in this part of the country, therefore, the information provided is
limited, while, the vapors have all time availability and have a significant contribution in the
hydrological cycle locally or over a regional scale. Hence for understanding the processes
altering the various sources, its isotopic signatures were studied. The Isotope Water Vapour Line
(Iso Val) was drawn together with the Global Meteoric Water Line (GMWL) and the best fit line
was δD= 5.42*δ18O+27.86. The precipitation samples were also collected during the study
period and were best fitted with δD= 8.20(±0.18)*δ18O+9.04(±1.16) in the Local Meteoric Water
Line (LMWL). From the back trajectory analysis of respective vapor samples, it is unambiguous
that three major sources viz; local vapor, western disturbance and monsoon vapor are controlling
the fate of moisture over Roorkee. The d-excess in ground-level vapor (GLV) reveals the supply
of recycled moisture from continental water bodies and evapo-transpiration as additional
moisture sources to the study area. The intensive depletion in isotopic ratios was associated with
the large-scale convective activity and low-pressure/cyclonic/depression systems formed over
Bay of Bengal.
