|
Relying on tree-ring derived estimates of the summer Palmer Drought Severity Index (PDSI) presented by Cook et al. (1999), this document investigates drought frequency, intensity, and duration in the San Antonio area for a 280-year period between A.D. 1700 and 1979. The PDSI is a widely used index that is based on several variables and is designed to monitor soil moisture conditions. In most circumstances, the PDSI varies between 4.0 and -4.0, with an average year falling between 0.5 and -0.5. Here, I define drought as a value of -1.0 or less on the tree-ring derived PDSI. Using this definition, there were 40 droughts reflected in this 280-year stretch, with the average drought lasting 1.8 years. Long-term droughts, defined as droughts exceeding three years in duration, occurred four times in the available data, with three of these four being in the 1700s, and the fourth occurring in the early 1950s. This 1950s drought, covering a six-year period, was both the longest drought reflected in the available records as well as the most intensive of the four long-term droughts.
|
