by Stella Jes Varghese, Sajani Surendran, Kavirajan Rajendran and Akio Kitoh
Abstract: Present-day simulations (1983–2003) of a global climate model of 60-km resolution with three deep convection schemes are analysed to find the best scheme for simulation of mean Indian summer monsoon rainfall (ISMR) and its variability. Multiforcing ensemble projections with the best scheme are carried out under multiple Representative Concentration Pathways (RCPs) (based on various socio-economic and technological development at the end of the century), viz. RCP2.6, RCP4.5, RCP6.0 and RCP8.5, forced with four patterns of future sea surface temperature (SST) change for each scenario; one with mean SST changes projected by 28 Coupled Model Intercomparison Project Phase-5 (CMIP5) models and the rest obtained from subgroups of CMIP5 models grouped through cluster analysis of tropical SST changes. These are analysed for future (2079–2099) changes in surface air temperature (Ts ) and rainfall which show overall increase over India except for rainfall reduction over Western Ghats. We find that combination of enhanced atmospheric water vapour content and increased vertically integrated low level moisture transport into the subcontinent as the major contributing factors for future intensification of ISMR. Extreme events show increase in warm days with significant increase in warm nights. Percentage of grid points showing increased extreme rainfall increases from low to high emission scenario. The high-resolution model enables to study projected changes over India at homogeneous zones level. The maximum increase in Ts and rainfall occurs over Western Himalaya and Northeast hilly region respectively. Consistent with future increase in Ts and rainfall, their extreme events also increase over all the homogeneous zones.
by C. DeMets, S. Merkouriev and S. Jade
We reconstruct the movement of the India Plate relative to Eurasia at ≈1-Myr intervals from 20 Ma to the present from GPS site velocities and high-resolution sequences of rotations from the India–Somalia Antarctic–Nubia–North America–Eurasia Plate circuit. The plate circuit rotations, which are all estimated using the same data fitting functions, magnetic reversal sampling points, calibrations for magnetic reversal outward displacement, and noise mitigation methods, include new India–Somalia rotations estimated from numerous Carlsberg and northern Central Indian ridge plate kinematic data and high-resolution rotations from the Southwest Indian Ridge that account for slow motion between the Nubia and Somalia plates. Our new rotations indicate that India–Somalia plate motion slowed down by 25–30 per cent from 19.7 to 12.5–11.1 Ma, but remained steady since at least 9.8 Ma and possibly 12.5 Ma. Our new India–Eurasia rotations predict a relatively simple plate motion history, consisting of NNE-directed interplate convergence since 19 Ma, a ≈50 per cent convergence rate decrease from 19.7 to 12.5–11.1 Ma, and steady or nearly steady plate motion since 12.5–11.1 Ma. Instantaneous convergence rates estimated with our new India–Eurasia GPS angular velocity are 16 per cent slower than our reconstructed plate kinematic convergence rates for times since 2.6 Ma, implying either a rapid, recent slowdown in the convergence rate or larger than expected errors in our geodetic and/or plate kinematic estimates. During an acceleration of seafloor faulting within the wide India–Capricorn oceanic boundary at 8– 7.5 Ma, our new rotations indicate that the motions of the India Plate relative to Somalia and Eurasia remained steady. We infer that forces acting on the Capricorn rather than the India Plate were responsible for the accelerated seafloor deformation, in accord with a previous study. India–Eurasia displacements that are predicted with our new, well-constrained rotations are fit poorly by a recently proposed model that attributes the post-60-Ma slowdown in India–Eurasia convergence rates to the steady resistance of a strong lithospheric mantle below Tibet.