Dry event trends and frequencies in the south central United States

In this study, dry spells in the southern United States are analyzed. Dry spells are defined as consecutive days with no recorded rainfall. Seventy (70) weather stations are researched in Texas, Oklahoma, Louisiana, Arkansas, Mississippi, and Tennessee. Daily precipitation for each station identifies potential trends in consecutive dry days. Stations were selected for their completeness, longevity, and their proximity to one another. Only stations with five percent or less missing data were allowed. All 70 stations will be analyzed from 1950-2008. Twenty-four stations possess over 100 years of data and will be analyzed. The best geographical indicator for consecutive dry days across this region is longitude, where dry spells have longer durations at westernmost stations. Longitude is a good indicator of changes in frequencies across the study area due to natural climatological controls. Continental tropical (cT) airmasses that exist mainly over Mexico and the southwestern United States compared to the maritime tropical (mT) airmass over the Gulf of Mexico influence precipitation in this area. Moving west from 95°W, there is a steep gradient in dryness of the selected stations. This is the point in which the maritime tropical airmasses lose its influence over the region. Annual average dry spells are calculated. Results from this analysis illustrate more positive tendencies than negative for the years 1908-2008. Annual maximum dry spells are also determined, which show a tendency toward shorter duration events overtime (71.4% of stations). Longer annual maximum dry spells also occur in the west. These tendencies support the idea of climate change, increasing temperatures, and therefore more rain days. Return periods for these events are also presented to further analyze the climatology of dry spells in this region for the 2-, 5-, 10-, 25-, 50-, and 100-year events. Steep gradients are discovered in the western half of the study area. From near 95°W eastward, the gradient is much less evident. Results from this research should assist those in the agriculture industry, water resource management, and the many others who depend on high-quality forecasts of precipitation. This analysis also aims to benefit decision and policy-makers in all levels of government