During the last decade, eastern Australia, South Africa and the Southwest of the USA have all experienced prolonged drought. The impacts on water supply are so severe that some townships have had to plan for ‘day zero’, where town water is no longer accessible. However, it is not the first time that such droughts have impacted geographically discrete regions.  Indeed, a study by Verdon-Kidd and Kiem (2014) identified periods of drought synchronicity across the southern hemisphere since 1900. Droughts are, and always will be, part of the hydroclimate and it is impossible to prevent these natural disasters from occurring. Improved quantification of the frequency, magnitude and duration, as well as a better understanding of the mechanisms that cause enhanced risk periods are essential to effectively manage and minimize the damage associated with droughts when they occur. With the development of continental “tree-ring drought atlases” spanning centuries (gridded drought reconstruction developed from primarily tree ring records), we now have the ability to study spatial phasing of drought over a greatly extended time period. In this study we apply various statistical techniques (wavelet, clustering and hotspot analysis) to identify the temporal and spatial characteristics of drought across five regions (Australia/New Zealand, Mexico, Monsoon Asia, North America and Europe). Further, we identify trends in drought occurrence over the last five centuries and highlight regions where contemporary drought frequency exhibits deviance from the long term trends. We also examine these drought atlases for evidence of global drought synchronicity over the past 500 years.

Verdon-Kidd DC, Kiem AS, 'Synchronicity of historical dry spells in the Southern Hemisphere', Hydrology and Earth System Sciences, 18 2257-2264 (2014)

Drought atlas: http://drought.memphis.edu/