Review of Drought Worse Than Drought of Record Monitoring Methods for the Lower Colorado River in Texas

摘要

The State of Texas has issued water rights permits for Lakes Buchanan and Travis that allow the Lower Colorado River Authority to make water available to both firm and interruptible customers. Firm customers can be supplied in an amount up to the firm yield. Interruptible water may be available when firm demands are less than the firm yield, but interruptible supplies are cut off under drought conditions. The drought of record in this region of Texas occurred from 1947 to 1952, during a period of low inflow from 1946 through 1957. As a safeguard for firm customer supplies, the state permit requires that LCRA establish criteria to monitor for a drought worse than the drought of record and declare that a current drought is worse than the drought of record if conditions warrant. If a drought worse than the drought of record is declared, measures are taken to extend firm supplies. In this study, LCRA's current method for monitoring and declaring a drought worse than the drought of record and candidate replacement methods were evaluated. The study found that in addition to being difficult to communicate, the current method could overlook a moderate drought of extended duration. The study investigated Precipitation Indicators, Drought Indices, and regionally focused methods. Candidate methods were the Reservoir Deficit Index Method, a Revised LCRA Method and the Cumulative Runoff Deficit Method. Each of these would be an appropriate measure of drought intensity and would provide a legitimate determination of a drought worse than the drought of record. However, each has benefits and shortcomings that must be weighed against ease of communication and computation.