Academy of Scientific and Innovative Research (AcSIR)
CSIR-FOURTH PARADIGM INSTITUTE (CSIR-4PI)
NAL Belur Campus, Wind Tunnel Road, Bangalore-560037
PhD Thesis Oral Examination/Viva-Voce
TITLE: Impact of resolution and deep convection scheme on simulation of Indian summer monsoon and its projection under multiple RCPs using multiforcing ensembles
Stella Jes Varghese
(AcSIR Enrol. No. 10PP14A45002)
DATE & TIME: 25th May 2021 (Tuesday) at 11:00 AM
VENUE: Google Meet (Join with https://meet.google.com/dif-nrvx-vca )
Advanced climate models help to achieve improved phase relationship and teleconnection between tropical convection and sea surface temperature variation in the tropical Indian and Pacific Oceans. Still, Indian summer monsoon (ISM) rainfall and its variability remain a challenging feature to simulate due to the large gap in understanding its dynamics and associated physical processes. Skilful simulation of mean ISM is mandatory for reliable ISM projection which is imperative for policy decisions and efficient resource management. The skill of the current state-of-the-art climate models and NCEP CFSv2, the National Monsoon Mission Model of MoES, GoI, is assessed and found to be deficient in simulating important features of ISM rainfall. Multiphysics ensemble simulations are made using MRI global climate model at very high resolutions to identify the right combination of spatial resolution and deep convection parameterization for the representation of ISM rainfall. Higher resolution and incorporation of the most suitable deep convection scheme, are found to yield improved simulation of regional and local scale features of ISM rainfall particularly over the orographic regions.
This MRI global model climate at 60-km horizontal resolution is then used for obtaining multiforcing ensemble projections of ISM under 4 climate change scenarios known as the Representative Concentration Pathways (RCPs) of RCP2.6, RCP4.5, RCP6.0 and RCP8.5. Projected changes show overall increase in surface air temperature (~1°C, ~2°C, ~2.5°C and ~4°C respectively) as well as rainfall (~0.12mm/day, ~0.43mm/day, ~0.67mm/day and ~1mm/day respectively) averaged over India during the summer monsoon season. The mechanisms behind the projected change in ISM rainfall are also investigated. A combination of increased water vapour in the atmosphere along with increased low-level moisture transport into the subcontinent are the major contributing factors towards future enhancement of rainfall under RCP scenarios. However, the changes in monsoon rainfall over India, are not as uniform as those in temperature, with significant reduction in rainfall projected over the Western Ghats. High-resolution projection enables us to study the projected changes in extreme rainfall and temperature events over India as well as over different homogeneous zones. Warm nights are projected to increase much larger than warm days in the future. Maximum increase in surface air temperature and rainfall are projected over Western Himalaya and Northeast hilly regions respectively.
The projected changes in ISM can have large implications on various sectors of the economy such as agricultural management, water resource management and fisheries. Using the projected climate change information, future change in rice yield over a representative agricultural station in the state of Kerala is also investigated. Consistent increase in maximum and minimum temperatures along with decrease in rainfall is projected for the station. Resultantly, in future, the rice crop is found to attain early physical maturity due to the accumulated heat which ultimately reduces the rice yield. Delayed planting date is found to give more yield in future in the central zone of Kerala. Short duration, temperature tolerant varieties are suggested for better water efficiency in future.
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