Each state agrees that, when authorized by the legislature pursuant to the constitutional processes, it will from time to time make available to the board such funds as may be required for the expenses of the board as authorized under the terms of this compact. The contribution of each state for this purpose shall be in the proportion that its population bears to the total combined population of the states who are parties hereto as shown from time to time by the most recent official published report of the Bureau of the Census of the United States of America, unless the board shall adopt another basis in making its recommendation for appropriation to the compacting states.