In the case of an emergency or disaster occurring after the time of making the annual estimate of costs, declared to be such by resolution of the board, the board of the district may incur additional obligations and issue valid warrants therefor in excess of such estimate, in the manner provided by law for issuance of warrants by districts and the servicing thereof. All such warrants so issued shall be valid and legal obligations of the district and its taxable lands and improvements as shown upon the then current roll of the district filed with the county treasurer.