Question

under what circumstances can the salaries and allowances of the judges of a High Court be reduced?

Answer 1

The salaries and allowances of any Judge, be it of High Court or Supreme Court, can only be reduced during a Financial Emergency. Since their salaries are drawn on the Consolidated Fund of that state, they are not subject to vote in the Assemblies. 

Answer 2

Financial Emergency when the state doesn't have adequate funds to run the government.