FUTURE PROBLEMS OF DUST AND THE DUST HAZARD The estimation of future effects on the dust hazard in Arizona can only

be speculative at best. The possible natural influences may be discussed in terms of a signal of the climate system that is near-periodic or monotonic over time, such as the El Nino Southern Oscillation Index (ENSO) and CO2-induced climate changes. (The Southern Oscillation is a fluctuation of the inter-tropical general circulation while El Nino is an occasional warning of the western Pacific Ocean which can affect atmosphere conditions world-wide).

El Nino and the Southern Oscillation (ENSO) have been linked dynamically to alterations in climate of the south-west USA in two studies. In the first, Carleton (1987) states that no statistically significant relationship was found between the atmospheric circulation over the south-west USA and the coupled tropical sea surface temperature/ atmospheric index representative of the Southern Oscillation (SOI) for the period 1945–1984. Significant lag correlations were found between Carleton’s summer synoptic circulation index and Figure 7.15 (a) Winter (November-April) precipitation totals and mean PDSI, and (b) summer (May-September) precipitation totals and mean PDSI. These values are mean spatial values for a 51000km² area surrounding Phoenix, AZ:

the so-called South Central Climatic Division (modified after Brazel and Nickling, 1987).

Future problems of dust and the dust hazard

Blowing dust and highways 158

the SOI for 1945–1963 and 1964–1984. However, the south-west USA circulation-SOI teleconnections were deemed unstable over time, and thus not predictable. Brazel (in press) found insignificant correlations between Carleton’s summer synoptic index and dust-storm frequencies for central Arizona sites. However, Andrade and Sellers (1988) report a positive relationship between rainfall in Arizona (March-May and September-November) and moderate-to-strong El Nino events over the time period 1899–1983.

More study is needed to establish the nature of periodic circulation changes regionally and globally and their links to surface-climate changes in dust-prone environments of the south-west USA and Arizona. Strong El Nino generation is quasi-periodic, with periodicity of 11±5 years. There may be some predictability between El Nino trends and critical antecedent moisture that affects dust potential in central Arizona.

The clearest signal expected by the year 2065 is the doubled CO2 and trace-gas warming effect (NAS 1983). Based on prevailing scenarios from model output-gridded temperature and precipitation data of several global climate models, a scenario can be developed on the depletion/supply water ratios for Arizona. State projections on these ratios have been developed not accounting for climate change, but accounting for expected water-consumption changes by the year 2020 (Arizona Water Commission 1977) with high, medium, and low estimates for that year. The most probable ranges of the depletion/

supply ratios associated with the ensemble effects of CO2 warming/

drying anticipated for Arizona. In the absence of climate changes, water-use depletion/ supply ratios are anticipated to drop due to cutbacks of agricultural land in Arizona have been calculated. With future climate change (+2°C, –10% precipitation) due to CO2, the depletion/supply ratios could escalate to 1.23–2.06. Thus further stringent controls on water use may take place.

The implications for dust generation are staggering. Natural climate effects would act to reduce natural vegetative growth on desert surfaces and increase the frequency of drought conditions. Much more land may be retired from agriculture and remain idle. Increased recreational uses of land and construction activity pressures could mean a more severe blowing-dust hazard when wind storms occur. Unknown, of course, is how wind potentials and storm frequencies will vary due to climate change.

The dust hazard must be addressed more intensively in the future.

The dust problem is certainly complex and may be partially overcome with careful consideration of land-use planning. Strict air-quality regulations on particulates may in the future represent a negative feedback to the dust hazard in the coming years. However, land near

References 159 highways and in the surrounding region must be given special attention by federal, state, and local transportation officials and scientists in ordtfr to minimize potential adverse effects by future climate. The transportation planners, together with environmental scientists and highway meteorologists, must safeguard the highway systems against the vagaries of future climate changes.

7.6 REFERENCES

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Marcus, M.G. (ed.) (1976). Evaluations of Highway Dust Hazards Along Interstate Route 10 in the Casa Grande-Eloy Region, Final Report, Arizona Dept. of Transportation and Research Paper No. 3, Center for Environmental Studies, A.S.U., Tempe, AZ.

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Nickling, W.G. and Gillies, J.A. (1986). Evaluation of Aerosol Production Potential of Type Surfaces in Arizona, EPA Contract No. 68–02–388, MND Associates, 84pp.

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