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Recent Scientific Papers

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A Long View of Southern California Water Supply: Perfect Droughts Revisited

[[1]]

C.A. Woodhouse D.M. Meko E.R. Bigio First published: 08 January 2020
Journal of the American Water Resources Association

Abstract

The impact of drought on water resources in arid and semiarid regions can be buffered by water supplies from different source regions. Simultaneous drought in all major source regions — or perfect drought — poses the most serious challenge to water management. We examine perfect droughts relevant to Southern California (SoCal) water resources with instrumental records and tree‐ring reconstructions for the Sacramento and Colorado Rivers, and SoCal. Perfect droughts have occurred five times since 1906, lasting two to three years, except for the most recent event, 2012–2015. This number and duration of perfect droughts is not unusual in the context of the past six centuries. The modern period stands out for the relatively even distribution of perfect droughts and lacks the clusters of perfect drought documented in prior centuries. In comparison, perfect droughts of the 12th Century were both longer (up to nine years) and more widespread. Perfect droughts of the 20th and 21st Centuries have occurred under different oceanic/atmospheric patterns, zonal and meridional flow, and ENSO or non‐ENSO conditions. Multidecadal coherence across the three regions exists, but it has varied over the past six centuries, resulting in irregular intervals of perfect drought. Although the causes of perfect droughts are not clear, given the long‐term natural variability along with projected changes in climate, it is reasonable to expect more frequent and longer perfect droughts in the future.

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Bias correction of paleoclimatic reconstructions: A new look at 1200+ years of Upper Colorado River flow

[[2]]

Scott M. Robeson, Justin T. Maxwell, Darren L. Ficklin
Geophysical Research Letters

Key points

1. Bias correction makes paleoclimatic models more comparable to observations
2. After bias correction, the 1100s Colorado River megadrought became more extreme
3. The early 1600s Colorado River pluvial rivals that of the early 20th century after bias correction

Plain Language Summary

To study past climates, scientists use indicators such as tree‐ring widths that are related to temperature, precipitation, or streamflow. While these indicators usually are very reliable, they sometimes do not perform as well with extreme events such as intense droughts and wet periods. Here, we adopt a method that can correct for these limitations and apply it to a 1,200+year record of streamflow for the Upper Colorado River, a critical source of water for much of the southwestern United States. After using our method, we find that several extreme events from the tree‐ring record of streamflow were even more intense than formerly thought. In particular, the largest drought in the record that occurred during the 1100s was drier and longer lasting after our correction. During the 56‐year duration of the 1100s drought, our correction makes the flow in the river lower by nearly 52 × 109 m3 of water, which is the equivalent of 1.45 times the capacity of Lake Mead (the largest reservoir in the United States). And, while it was known that the early 1900s was among the wettest periods in the last 1,200+ years, we identify a period in the early 1600s that matches it.

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