Encumbrance for long term contracts at the stage of raising PR

Hi team,

Our requirement is like this. client is following advisory budgetory control. We have some long term contracts where at the time of creating PR we are raising PR with the full amount of the contract. But at the time of PO, we would issue PO for only that year budgeted amount. The disadvantage we are now having is at the time of PR it creates commitment for the full amount of contract where as the budget would be only for one year and there by the funds available will go into a negative variance.

Can we be helped to find a solution to manage these long term contracts maintaining the limits of budget for each year.