Conditions for the Dust Bowl to Happen Again

Was the Grit Bowl predictable?

Richard Seager
Lamont-Doherty Earth Observatory of Columbia Academy

"Dust Basin" by Alexandre Hogue (Missouri, 1898 - 1994)

Contempo modeling work (Schubert et al. 2004a,b, Seager et al. 2005) has claimed that the Dust Bowl drought of the 1930s was forced by small changes in tropical SSTs, substantially several persistent years of La Niña-like weather in the Pacific and a warm subtropical North Atlantic Sea, both of which are assumed to have had natural origins. If this is so then it means that, had the SSTs been known in accelerate, it would have been possible to predict that the drought was to occur and, possibly, the environmental and social catastrophe of the Dust Basin could have been ameliorated.

Fundamentally that would accept depended on being able to predict the SSTs and nosotros currently do not know if tropical SSTs are predictable to whatsoever useful caste beyond the interannual timescale with but a few studies having looked into this (Karspeck et al. 2004, Seager et al. 2004). Here we take a different tack and place ourselves in 1929 and ask the more limited question: If the SSTs in the 1930s were foreknown could the drought take been predicted? The paper (Seager et al. 2007) appeared in the Journal of Climate.

Using ensembles of atmosphere model simulations to assess predictability

To answer this we compare 16 member ensembles of model simulations of the 1930s forced by historical SSTs variously imposed globally, in the tropical Pacific lone and in the tropical Atlantic lonely. These simulations are compared with another ensemble which starts with the atmosphere and country initial conditions in January 1929 (taken from the global SST forced simulations) and integrates forward to 1940 but with the SST climatology of 1856-1928 imposed. This latter ensemble therefore ignores the influence of SST variations in the 1930s and looks to see if some combination of the atmosphere and state initial conditions and internal atmosphere-land variability could have produced a virtually decade-long drought.

Effigy i shows maps of the ensemble mean precipitation anomaly averaged over 1932 to 1939 relative to the precipitation climatology for that ensemble for 1856-1928. The observed atmospheric precipitation anomaly 1932-1939 minus 1856-1928 is too shown. The observed precipitation reduction covered most of the United States and was centered in the northern and central Plains. Unlike most historical droughts it as well impacted the northern Rocky Mountains states and the Pacific Northwest. The modeled drought with global SST forcing (GOGA) has the right magnitude merely was centered and extended too far south and did not impact the Pacific Northwest. The modeled drought was forced by both the tropical Pacific (POGA-ML ensemble) and tropical Atlantic (TAGA ensemble). In contrast, the ensemble with climatological SSTs (COGA) produces largely breathless and weak precipitation anomalies emphasizing that the real drought was in big function SST-forced. Hence, advance noesis of SSTs would accept led (with this model) to a prediction of a serious drought but i that extended too far due south and did not impact the Northwest.

Figure i. The observed (top left) and modeled precipitation anomalies during the Dust Basin (1932 to 1939) relative to a 1856 to 1928 climatology. Observations are from GHCN. The modeled values are ensemble means from the ensembles with global SST forcing (GOGA), tropical Pacific forcing (POGA), tropical Pacific forcing and a mixed layer ocean elsewhere (POGA-ML), tropical Atlantic forcing (TAGA) and with land and temper initialized in January 1929 from the GOGA run and integrated forrard with the 1856-1928 climatological SST (COGA). Units are mm per month.

Figure 2 shows statistics for the ensemble spread, ensemble hateful and observed precipitation averaged over the Great Plains, the Southwest and the entire West (see explanation for details). The ensemble with climatological SSTs produced precipitation anomalies that are not separated from climatology. In contrast the ensembles with SST forcing produce droughts that are well separated from climatology though clearly likewise strong in the Southwest and not strong enough in the West every bit a whole. Both Pacific and Atlantic SSTs contributed.

Figure 2. The lower quartile, median and upper quartile (shown by the box) and the lower and upper ranges (shown by the whiskers extending below and above the boxes) of the model ensembles for GOGA, COGA, POGA and TAGA for the Great Plains region (elevation), the Southwest (centre) and entire West (lesser). The observed value is shown as an asterisk. Units are mm per month.

Figure 3 shows maps for the surface air temperature anomaly. All the model simulations miss the remarkable extent and strength of warm anomalies in the 1930s. The observed warm pattern closely follows the design of precipitation reduction and is most likely a response to it. Thus the temperature prediction error follows from the precipitation prediction error. (As support for this, during the 1950s drought the model simulated quite realistic patterns of both precipitation reduction and temperature increase and over again their patterns coincide.)

Figure three. Same as Figure one simply for temperature. Units are Kelvin.

The curious spatial pattern of the Dust Bowl drought

No model ensemble member produced a spatial pattern of drought akin to that observed during the Dust Basin. That is, no mix of SST-forcing and internal variability was able to produce a Dust Bowl-like drought. Instead the model produces droughts centered in the Southwest and the southern and cardinal Plains. These are the regions most connected, via atmospheric circulation, to tropical Pacific and Atlantic SST anomalies. That pattern of teleconnections is quite similar to what tin can be deduced from observations and, hence, the northern and northwestern parts of the Dust Basin drought are hard to explain in terms of SST forcing solitary. Other models (NSIPP, GISS, GFDL), to the all-time of our noesis (since only one is published), also produced Dust Bowl droughts centered too far south. The 1950s drought is one that was centered in the regions of strongest teleconnection to tropical SSTs.

The inability to correctly model the spatial pattern of the Dust Bowl drought, and its deviation from the typical pattern of tropical SST-forced drought, makes u.s.a. wonder how unusual the Dust Bowl design was. Analyses of instrumental data since the mid nineteenth century - shows that none of the other v multiyear droughts in this interval (1856-65, 1870-77, 1890-96, 1948-57 and post 1998) had a similar pattern. For a longer record nosotros examined the updated version of the gridded tree ring records within the Due north American Drought Atlas. Computation of the spatial correlation between the Dust Bowl pattern and six year low laissez passer filtered data revealed just three prior droughts that had an anomaly correlation exceeding 0.4 (Figure 4). All were in the Medieval catamenia. No other droughts had an Air-conditioning exceeding 0.31 presenting a clear separation between Dust Bowl type droughts and the more commonly occurring blueprint with a center in the Southwest and southern and central Plains.

Figure 4. The tree ring reconstructed summer Palmer Drought Severity Index for the Dust Bowl drought and three prior droughts in the concluding millennium that had similar northern-centered patterns and without strong drought in the Southwest or Mexico. The information is from the updated version of the North American Drought Atlas of Cook and Krusic (2004).

Summary

1. SSTs during the 1930s forced a severe multiyear drought in Due north America.
2. Both tropical Pacific and tropical North Atlantic SSTs were involved in forcing the model drought
3. The model drought is statistically significantly distinct from annihilation that can happen in the presence of climatological SSTs.
4. The modeled Dust Basin drought was farther south than that observed and was non accompanied past the well-nigh-continental scale warming of the observed drought
5. The observed drought had a pattern that has non been seen since Medieval times when 3 droughts with this pattern occurred.

Clearly aspects of the Dust Basin drought could have been predicted in 1929 had advance cognition of SSTs been bachelor. This motivates increased effort to extend the predictability of tropical SSTs beyond the interannual timescale. The detail pattern of the Dust Bowl drought deserves special attending - including the possible role of the widespread devegetation and land surface degradation and dust aerosol loading during that decade, run across our Dust Bowl folio and the reference Cook et al., 2008. As well, Ben Cook has created an interesting pic of the dust loading in the GISS simulations of April to August 1934. View Movie. Information technology is notable that the last time droughts with that design occurred (during the Medieval period) at that place is also evidence of devegetation and dune mobilization (Forman et al. 2001).

Picture from Worster (1979) 'Dust Bowl; The Southern Plains in the 1930s', Oxford University Press. The 'they' refers to the Dalhart (TX) Chamber of Commerce which thought the Grit Bowl series of paintings by fellow southerner, Hogue, defamed the Due south and tried to buy this painting to burn down on the streets of Dalhart.

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References:

• Cook, B.I., R.L. Miller and R. Seager, 2008: Dust and bounding main surface temperature forcing of the 1930's 'Dust Bowl' drought. Geophysical Research Letters, Vol. 35, L08710, doi:x.1029/2008GL033486. PDF
• R. Seager, Y. Kushnir, Chiliad.F. Ting, M. Cane, N. Naik and J. Velez, 2008. Would advance cognition of 1930s SSTs have allowed prediction of the Dust Basin drought? Journal of Climate, 21, p. 3261-3281. DOI: 10.1175/2007JCLI2134.1. PDF
• Seager, R., Y. Kushnir, C. Herweijer, N. Naik, and J. Velez: 2005. Modeling of tropical forcing of persistent droughts and pluvials over western North America: 1856-2000. J. Climate, 18, 40684091. PDF
• Cook, E. R. and P. J. Krusic: 2004. North American Summer PDSI Reconstructions. Technical Report 2004-045, IGBP PAGES/World Data Heart for Paleoclimatology Data Contribution Serial, Bedrock, CO, USA.
• Karspeck, A., R. Seager, and K. A. Pikestaff: 2004. Predictability of tropical Pacific decadal variability in an intermediate model. J. Climate, 17, 28422850. PDF
• Schubert, Southward. D., M. J. Suarez, P. J. Region, R. D. Koster, and J. T. Bacmeister: 2004a. Causes of long-term drought in the United States Cracking Plains. J. Climate, 17, 485503.
• Schubert, S. D., One thousand. J. Suarez, P. J. Region, R. D. Koster, and J. T. Bacmeister: 2004b. On the cause of the 1930s Grit Bowl. Science, 303, 18551859.
• Seager, R., A. Karspeck, M. Cane, Y. Kushnir, A. Giannini, A. Kaplan, B. Kerman, and J. Velez: 2004. Predicting Pacific Decadal Variability. Globe Climate: The ocean-atmosphere interaction , C. Wang and Due south.-P. Xie and J. A. Carton, ed., American Geo-physical Union, Washington, DC, 115130. PDF
• Forman, S., R. Oglesby, and R. S. Webb: 2001, Temporal and spatial patterns of Holocene dune activity on the Cracking Plains of Due north America: megadroughts and climate links. Glob. Planet. Change, 29, 129.

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Source: http://ocp.ldeo.columbia.edu/res/div/ocp/drought/dustbowl.shtml

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