Articles written in Journal of Earth System Science

    • Stable isotope characteristics of precipitation of Pamba River basin, Kerala, India

      T R Resmi K V Sudharma A Shahul Hameed

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      Stable isotope composition of precipitation from Pamba River basin, Kerala, India, is evaluated to understand the role of spatial and temporal variations on rainwater isotope characteristics. Physiographically different locations in the basin showed strong spatial and temporal variations. δ18O varied from −7.63 to −1.75‰ in the lowlands; from −9.32 to −1.94‰ in the midlands and from −11.6 to −4.00‰ in thehighlands. Local meteoric water lines (LMWL) for the three regions were determined separately and an overall LMWL for the whole of the basin was found to be $\delta^2$H = 6.6 (±0.4) $\delta^{18}$O+10.4 (±2.0). Altitude effect was evident for the basin (0.1‰ for $\delta^{18}$O and 0.8‰ for $\delta^2$δ2H per 100 m elevation), while the amount effect was weak. The precipitation formed from the marine moisture supplied at a steady rate, without much isotopic evolution in this period may have masked the possible depletion of heavier isotopes with increasing rainfall. Consistently high d-excess values showed the influence of recycled vapour, despite the prevailing high relative humidity. The oceanic and continental vapour source origins for the south-west and north-east monsoons were clearly noted in the precipitation in the basin. Rayleigh distillation model showed about 30% rainout of the monsoon vapour mass in the basin.

    • Stable water isotope signatures of dual monsoon precipitation: A case study of Greater Cochin region, south-west coast of India


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      Precipitation samples of various spatio-temporal scales were collected from coastal, midland and urban regions of Greater Cochin, Ernakulam district, Kerala for a period of 1 yr (2015–2016). The collected samples were analysed for stable water isotopes (SWI) ($\delta\rm{D}$ and $\delta^{18}\rm{O}$), to understand these variations in the precipitation source and the factors governing its isotopic characteristics during precipitation. The $\delta^{18}O$ in rainwater varies from -8.73 per thousand to 0.29 per thousand in urban, -12.21 per thousand to 2.59 per thousand in midland and -9.99 per thousand to 0.97 per thousand in lowland regions. Spatio-temporal variations in SWI were observed in various regions, suggesting altitude and continental effect followed by the establishment of a regional overall local meteoric water line (LMWL) $\delta\rm{D}$ = $8.06 (\pm0.15)\delta^{18}O + 12.5 (\pm0.68)$. Among the coastal, midland and urban regions, the highest slope ($\sim8.3$) and intercept($\sim13.0$) were observed in the urban region, which designates the variations in temperature along spatial and different layers of the atmosphere in the urban region, resulting in the deviation of isotopic characteristics.The overall deuterium excess ($d$-excess) value is $\sim10$ per thousand during the south-west monsoon (June–September), suggesting a moisture source of marine origin. A $d$-excess of $\sim13$ per thousand is observed during the north-east monsoon, indicating a moisture source from the continental contribution (October–December). The results of the moisture source obtained from the $d$-excess value are also supported by back-trajectory analysis. Thus, the present study on isotopic characterisation of precipitation and its controlling factor may enhance our understanding of the Indian monsoon and its dynamics in the west coast region of India.

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