The Occurrence of Extreme Monthly Temperatures and Precipitation in Two Global Regions

There has been a lot of focus on the occurrence of extreme weather events and a possible connection to climate change and variability. Much of this work has been related to individual events, rather than for long periods of time. This work will examine the occurrence of extreme conditions in the monthly temperature and precipitation for two geographically disparate regions of the Northern Hemisphere. These regions are the central USA (cUSA), and the southwest region of Russia (swRUS). The data were provided by the Missouri Climate Center for a 125 year period and the Russian Hydrometeorological Center for a 72 year period. For this study, an extreme temperature event was defined as a month that was two monthly or three seasonal standard deviations from the period mean. Since precipitation is not normally distributed, the three (two) wettest and driest months were chosen for the cUSA (swRUS) region in order to provide for a data set that was of similar size to the temperature data set for each region. The initial results demonstrate that in cUSA, there was preference for the occurrence of warm anomalies during eras of mean regional temperature increase and vice versa. For swRUS, there was a preference for the occurrence of cold anomalies early in the data set, and warm anomalies in the later part, although this period is one of steadily increasing mean temperatures for the region. There was a strong tendency in both locations for occurrence of extreme months during a preferred phase of the El Niņo and Southern Oscillation (ENSO). In cUSA (swRUS), there were fewer (more) extreme monthly temperature occurrences in the La Niņa phase. However, for monthly precipitation extremes in cUSA (swRUS) favored the La Niņa (El Niņo) periods. In both regions, there was no signal in temperature as related to longer-term climatic cycles, while for precipitation there were weak relationships to the Pacific Decadal Oscillation and the North Atlantic Oscillation. In both regions, cold monthly anomalies were associated with persistent and strong upstream blocking events.