At the beginning of each month during the fiscal year, the Mayor shall submit to the Council, data showing the relation between the estimated and actual income and expenses to date. If it shall appear that the income of the City is less than anticipated, the Council may reduce appropriations, except amounts required for debt and interest charges. At the end of each fiscal year, the unencumbered balance of any appropriation, except that for the payment of indebtedness, shall be deemed unappropriated.