"The impaired asset ratio of the banking system will inch up to 12.5 per cent, including ARC receipts but excluding discom bonds, by FY17," the agency said in its report on banking sector outlook for the next fiscal.
Stressed assets in this fiscal is estimated to be at 12 per cent as compared with 10.8 per cent in FY 2014-15.
The report said the credit costs are likely to remain high at around 120 basis points, given the low provision coverage as well as the recent push by the RBI to recognise the stress from levered corporates.
Though schemes like 5:25, strategic debt restructuring and Uday are likely to help contain headline impaired asset ratio, the stress from highly levered corporates will persist over the next few years, it said.
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"Indian banks may need up to Rs 1 trillion over and above the Basel III capital requirements to manage the concentration risks arising out of their exposures to highly levered and large stressed corporates," the report said.
All these exposures are currently treated as performing and carry a minimal loan loss provision of 5 per cent or less.
RBI has already asked banks to recognise some of these deeply stressed assets as non-performing and to make prudent provisions for them.
The shortfall may significantly increase the government's equity injection requirement compared to the Rs 70,000 crore announced on July 31, 2015, it said.
Of this, Rs 1 trillion about Rs 450 billion is expected
to come as part of the remaining tranches under the mission Indradhanush, a plan to revamp PSBs.
"Government support remains critical for PSBs, given their low internal accruals, eroded equity valuations and risk of further slippage from levered corporates," it said.
Development of AT1 market would be critical in next fiscal, given the significant requirement and the burden of very weak market appetite in FY 2015-16, it said.
The report said assuming 14 per cent CAGR in RWA for large PSBs, the total incremental tier-1 capital requirement is Rs 1.4 trillion (50 per cent CET1, 50 per cent AT1) with a strong frontloaded requirement for AT1 bonds.
While most of these large five PSBs have been proactive in testing the AT1 market with a combined issuance of Rs 65 billion so far, the requirement by FY 2016-17 will be another Rs 250 billion.
The rating agency said most private sector banks continued to improve their funding profile while PSBs reported high ALM gaps in FY 2014-15 and continue to show similar trends as per latest data into FY 2015-16.
It believes that the refinancing capability of government banks' remains strong, based on the strengths of their granular deposit bases and funding franchises.
"Banks with large ALM gaps may however witness higher funding costs due to elevated refinancing pressure, compromising their capability to effectively transmit monetary easing," it said.