Abstract
An analysis of the possible differences among various rainfall parameters during drought and nondrought periods was undertaken for 12 Texas stations. The division of monthly rainfall amounts into quintiles served as the rainfall classification. The Palmer Drought Index (PDI) proved to be inadequate as a classification because of its heavy emphasis on antecedent precipitation. Rainfall amounts, frequencies, and intensities were calculated for each quintile for four thresholds of rainfall 0.0254 cm, 0.2540 cm, 0.5080 cm, and 1.2700 cm. The thresholds were applied on a daily and hourly basis. Rainfall frequency in Very Dry periods proved to be less than 100% of normal at low rainfall thresholds in all cases except at Port Arthur in January (rain days at the lowest threshold were 127% of normal). This suggests that the opportunities for rainfall enhancement in Texas via cloud seeding are very limited. The possible differences in persistence of rainfall between Very Dry and Very Wet periods were examined by calculating runs of rain hours for the 0.0254 cm threshold. Medians of runs of rain hours in Very Dry periods were found to be less than those in Very Wet periods except at Corpus Christi in April and at Waco in February. Probabilities that a run of rain hours would extend to a given length were determined. During Very Dry periods a probability greater than 0.5 that a rain will extend into a second hour during a month of key importance to agriculture (June, July, and August) occurs only at Amarillo, Lovelady, Port Arthur, and Waco. The probability that a rain will extend into a third hour is never above 0.5 during the key months in Very Dry periods for any of the stations studied. This suggests that during Very Dry periods, attempts at seeding clouds already producing rain and efforts to cut irrigation costs by shutting down equipment during a rain would not be successful over most of the state.
Flynn, Michael Steven (1977). Variations in precipitation parameters between drought and nondrought periods in Texas. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -629747.