Quantifying Raindrop Evaporation Deficit in General Circulation Models from Observed and Model Rain Isotope Ratios on the West Coast of India

Raindrop evaporation is an important sub-cloud process that modifies rainfall amount and rainwater isotope values. Earlier studies have shown various general circulation models (GCMs) do not incorporate this properly during the simulation of water ratios (oxygen hydrogen). Our recent study has demonstrated inadequate estimation for Indian Summer Monsoon (ISM) results in significant biases (model-observed values) GCMs on a monthly scale. However, quantitative was lacking. The magnitude raindrop depends upon ambient humidity temperature, which vary considerably ISM. Consequently, would also over time scales. present aims to investigate scale variation simulations its causal connection with corresponding biases. Towards this, we compare 11-year-long (1997–2007) dataset rain (both oxygen hydrogen) from station, Kozhikode (Kerala), obtained under Global Network Isotopes Precipitation (GNIP) programme International Atomic Energy Agency (IAEA) outputs two isotope-enabled nudged GCMs—ISOGSM LMDZ4. fractions are estimated 44 ISM months (June–September) period using Stewart (1975) formalism. Using simple condensation–accretion model based equilibrium fractionation vapour, adopted vapour profiles, estimate liquid at cloud base. Considering as initial rain, observed hydrogen surface samples. show strong positive correlations (R2 = 0.60 0.66). This suggests lower estimates could be responsible these GCMs.