To build an earth systems model (ESM) appropriate for detection, attribution and projection of changes in the South Asian monsoon, the state-of-the-art climate forecast system (CFS) model has been transformed to a climate model suitable for extended climate simulations at the Centre for Climate Change Research (CCCR), Indian Institute of Tropical Meteorology (IITM), Pune.
The development of IITM-ESM was achieved by incorporating a new ocean component, including marine biogeochemistry and ecosystem modules, in the CFS global coupled model. The IITM-ESM simulations produce more realistic distribution of sea surface temperature (SST) as compared to the CFS model which had a prominent cold SST bias. Incorporation of more realistic ocean processes in the IITM-ESM, compared to the CFS model, leads to alleviation of the cold SST bias by nearly 0.8oC in the global mean SST. Besides this, the incorporation of realistic tropical convection and flux exchanges across the atmosphere-ocean-land-ice components in the ESM have resulted in improved simulation of the South Asian monsoon rainfall, dominant modes of climate variability and ENSO-Monsoon teleconnections.
Further improvements in the IITM-ESM model since January 2015 to obtain a radiatively-balanced global climate modelling framework enables reliable long term climate projections.
In the latest version (ESM2.0), the net energy imbalance at the top of the atmosphere is less than 1 Wm2 and incomparable with state-of-the-art climate models from around the world. More recently, scientists have also incorporated aerosol forcing (natural and anthropogenic) in the IITM-ESM which would enable the model to understand the radiative effects of aerosols on the global climate, and monsoon in particular. Also the IITM-ESM takes into account interactive ocean biogeochemical processes, and provides an excellent opportunity to understand the impacts of climate change on the regional monsoon precipitation and wind patterns and the primary productivity and chlorophyll variability of the Indian Ocean. The IITM-ESM will be participating in the next Intergovernmental Panel for Climate Change (IPCC) Coupled Model Intercomparison Project phase six experiments—this is a first for an Indian climate model.
CORDEX South Asia
IITM-Pune’s CCCR is also leading the Coordinated Regional Downscaling Experiment (CORDEX) for the South Asian region. CORDEX is an international programme under the World Climate Research Programme (WCRP) which aims at advancing and coordinating the science and application of regional climate downscaling through global partnerships, to help local and national climate adaptation strategies.
The regional modelling activities of CORDEX South Asia are focused on providing reliable projections in much greater detail (than global climate models), with more accurate representation of localised extreme events over the South Asian region, through:
- Development of high-resolution (50 km) multi-model ensemble projections of regional climate change scenarios for South Asia. These projections are generated by CCCR-IITM and various international partner institutions;
- Development of an earth system grid (ESG) node at CCCR-IITM for archiving, management and dissemination of CORDEX South Asia datasets;
- Evaluation of regional climate projections over South Asia for reliable climate change information for effective harnessing of science based information on vulnerability, impact, and adaptation of communities; and,
- Development of regional capacity for assessing regional climate change.
As part of this activity, high-resolution simulations of 20th century climatic variations and climate projections for the future (21st century) have been developed at CCCR-IITM, using a global climate model with telescopic zooming over the South Asian region (~35 km in longitude x 35 km in latitude). These high-resolution simulations offer improved opportunities to understand several key regional scientific issues concerning climate change over South Asia—e.g., monsoons, precipitation extremes, heat waves, droughts and floods, changes in cyclonic weather systems, and hydrological cycles. A variable resolution global modelling framework, based on the Laboratorie Dynamique Meteorologie (LMD, France) atmospheric general circulation model (GCM), has been employed for this purpose under a scientific collaboration between CCCR-IITM and LMD, aimed towards contributing to the IPCC AR6 assessment. The high resolution climate projections for India (2006-2095) were released at the Sixth National Workshop on Climate Change organised at INCOIS, Hyderabad in September , 2014.
The IITM’s CORDEX programme is not only helping better understanding of South Asian climate variations, but aiming to disseminate scientific information on vulnerability and adaptation strategies adopted by communities. This can help India cope with the worst effects of climate change.