Drought Atlases and Water Supplies: Past Impacts for Future Consideration

Drought Atlases and Water Supplies: Past Impacts for Future Consideration

Ed Cook and Brendan Buckley take a core sample from a tree in Nepal.

Trees provide a history of climate variation in their rings as they grow. Pencil-thin core samples allow scientists to study the changes.

Ed Cook and colleagues develop tree rings chronologies that tell the story of changing drought conditions across wide expanses of the globe. Their first three drought atlases – covering North America, Monsoon Asia, and Europe and the Mediterranean – provide a new view of historic droughts and extreme precipitation across the Northern Hemisphere going back thousands of years that can be used to better understand weather patterns and forecast risks ahead.

The development of continental-scale drought atlases from long tree-ring records has fundamentally altered our understanding of how variable and long lasting changes in drought and wetness have been in the past and could be in the future.

The first of these drought atlases was produced for North America in 2004. The North American Drought Atlas (NADA) revealed the occurrence of megadroughts lasting several decades or more during medieval times in the American West. These megadroughts include one that led to the abandonment of the Mesa Verde cliff dwellings by the Anasazi Indians by around 1300 AD. The second drought atlas was produced for Asia in 2010. The Monsoon Asia Drought Atlas (MADA) also revealed megadroughts, including a span that is believed to have contributed to the demise of the Khmer civilization at Angkor in present day Cambodia.

The Northern Hemisphere drought atlases provide a larger picture of climate variability. The bottom maps show two opposite extremes from the Old World Drought Atlas. (Cook, et al. 2015)

The Northern Hemisphere drought atlases provide a larger picture of climate variability through time. (Cook, et al. 2015)

The newest drought atlas was produced for Europe, the Middle East, and North Africa in 2015. The Old World Drought Atlas (OWDA) also provides evidence of unusual megadroughts over parts of Europe during medieval and later times. The figure at right shows the locations of the three Northern Hemisphere drought atlases and two annual maps of wetness and dryness extracted from the Old World Drought Atlas. Extreme wetness in 1315 led to wide spread famine in western Europe because it was too wet to plant and harvest crops. Extreme drought in 1540 lead to severe water shortages in central Europe.

The causes of these and other extreme events in the drought atlases can be investigated using climate models. Doing so will enable us to better understand the likelihood that similar variability will occur in the future. This has clear societal implications. In the future, the drought atlases will be extended across unrepresented area in Asia and also down to the Southern Hemisphere to provide a comprehensive evaluation of past drought and wetness there, as well.  — Ed Cook