Moisture sources over Indian Sub-continent: Insights from Precipitation Water Isotopes

Singh, Nandan (2023) Moisture sources over Indian Sub-continent: Insights from Precipitation Water Isotopes. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Nandan Singh (18MS039)) Thesis_18MS039.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

The isotopic signature of the precipitation is largely connected to the various sources of moistures responsible for the precipitation. It can also be used to trace the effects of moisture sources and mechanism around it, by analysing the seasonal changes in the compositions of stable isotopes of water. Precipitation in Indian sub-continent occurs throughout the year but the main precipitation event is the Indian Summer Monsoon (ISM). There are two broad sources of moisture responsible for this precipitation, Oceanic and the Continental Sources. Oceanic moisture sources include the moisture contributions from ARAB (Arabian Sea, Red Sea, Gulf of Oman), BoB (Bay of Bengal), the Indian Ocean (IO) and the Western Pacific Ocean (PCO). Continental moisture sources include the transpiration, open water evaporation. bare soil evaporation and canopy interception loss. Together they cause monsoonal as well as non-monsoonal precipitation in the whole Sub-continent. The precipitation event has been divided into three different seasons namely, Pre-Monsoon (PM), Monsoon (M) and Post- Monsoon (PoM). During the PM season, the precipitation contains more heavier isotopes whereas during M season it decreases sharply and regains to a certain extent during the PoM season. For d-excess, the values hit its lowest in PM season, nearly constant (but low) during the M-season and highest during the PoM season. Since we know already that d-excess will be high whenever the of continental moisture contribution is higher than the Oceanic Moisture source, hence it is highest in PM season and then decreases out continuously in M and PoM season. Continental sources have its contributions highest in PoM season as the d-excess values are highest in this period. For most of the stations there is negative correlation of δ¹⁸O and dexcess values during PM and PoM season respectively except for Falakata and Kolkata which means that here, the effect of local Raindrop Reevaporation (RR) dominates over upwind Evapotranspiration (ET) whereas for sites like Kozhikode and Hyderabad, negative correlation can be seen in all the three season which signifies the inverse.

Actions (login required)

View Item