Pacific sea surface temperature and precipitation in the Southern Great Plains

In the first part of this study, monthly and seasonal precipitation values for selected climate divisions in the Great Plains are compared with global atmospheric and oceanic circulation indices. The global indices include El Nino-Southern Oscillation indices, as well as other north Pacific, Atlantic and continental circulation indices. Simple and multiple correlation analyses between precipitation and global circulation indices have been conducted. The results of this analysis confirms findings of earlier studies that showed that the tropical Pacific Sea Surface Temperature (SST) is one of the most relevant indices, particularly for winter precipitation in the Southern Great Plains. Despite this relative importance of the tropical Pacific SST index compared to other global indices, its ability to explain monthly and seasonal variations in precipitation in the Great Plains remains weak with less than 50%, and in most of the case less than 30%, of the precipitation variance explained by the index.

In the second part of this study, decade scale variations of precipitation in the Great Plains and their relationship to tropical Pacific SST are investigated. At the decade time scale, monthly and seasonal cycles in the SST indices and related variations in precipitation are filtered out, and long term trends in SST and precipitation become apparent. Five regions within the Great Plains that have similar patterns in their precipitation variation have been identified. Three of these regions cover most of the states of Nebraska, Kansas, Missouri, Oklahoma, Arkansas, Louisiana and Texas. These three regions show a pronounced wet period during the last two decades and a gradual, yet significant, increase in precipitation since the 50's. Over the last several decades, a warming of the tropical Pacific SST has also been observed. The decade scale fluctuation of the precipitation of the three regions correlates well with the decade scale fluctuation of the tropical Pacific SST (r2 ~ 60% to 80%). This relation is stronger in the central part of the Great Plains than along the Texas gulf coast.

This study suggests that the tropical Pacific SST and precipitation in the Great Plains are linked in some indirect fashion. The correlation is strong when the data is analyzed on a temporal scale of decades, and it is weak when the data is analyzed on an annual time scale. From these results one may speculate that the tropical Pacific SST and precipitation in the Great Plains are strongly linked, but that on an annual time scale other factors obscure and weaken the relationship.