Seeing Drought in Real Time

My friend Malcolm, who lives in Sydney, has some fascinating observations today on how hard it is to see drought as it is happening, something he (interestingly) noticed after returning to Sydney following a visit to a wetter place:

When you live in an area that changes by degrees month to month and year to year, you don’t automatically realise how large the accumulated change is. Particularly when it’s “home” and one’s reference point for “normal”. Looking around in the few days since I’ve been back, the signs of low rainfall are everywhere. Things don’t look any different than they did before, but having been exposed to the alternative for a while, it’s interesting to look with fresh eyes and notice the accumulated effect.


  1. Semi-OT, FYI:

    “Millennial-scale dynamics of valley fills over the past 12,000 14C yr in northeastern New Mexico, USA

    “Daniel H. Mann, Institute of Arctic Biology and Alaska Quaternary Center, University of Alaska, Fairbanks, Alaska 99775, USA; and David J. Meltzer, Department of Anthropology, Southern Methodist University, Dallas, TX 75275, USA. Pages 1433-1448.

    “The moisture regime of the western United States is the result of annual-to decadal-scale climate fluctuations embedded in millennial-scale ones that have occurred since at least the end of the last ice age. Mann and Meltzer used radiocarbon-dated charcoal to describe the timing of cycles of valley incision and aggradation in northeastern New Mexico over the past 12,000 years. Their results show that nine periods of valley aggradation separated by incision episodes occurred during this interval. Changes in precipitation tied to the strength of the North American monsoon system probably drive these cycles of aggradation and incision. When the monsoon is strong, more frequent summer thunderstorms cause increased flooding in small watersheds. Wetter summers spanning from decades to centuries allow forest vegetation to spread, which reduces sediment input from hill slopes at the same time floods are eroding away valley fills. Aggradation of valley fills probably occurs when summer thunderstorms are less frequent and large floods are correspondingly rare. Prolonged summer drought reduces forest cover, which increases erosion from slopes and causes sediment to accumulate in valleys. The geomorphic cycles Mann and Meltzer describe reflect a previously unrecognized, millennial-scale climate oscillation important in shaping the landscapes of the southern Great Plains. Depending on the phase of this millennial oscillation, human-caused changes in the environment may be dampened or enhanced. The millennial cycle is currently in its moist, incision phase, but in the past such incision phases have been short-lived compared to the dry phases.”

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