THE CHANGING FREQUENCY OF DUST STORMS 

THROUGH TIME 

A. S. GOUDIE and N. J. MIDDLETON 

Environmental Change Unit, School of Geography, University of Oxford, Mansfield Road, Oxford 

OX1 3TB, England 

Abstract. Dust storms are major, but under-studied actors in the world's drylands. 

Not only are they an important manifestation of desertification and land degradation, but they also have a whole suite of important environmental impacts, including possible rainfall suppression (Maley, 1982), fertilization of offshore areas, and 

disturbance to satellite communications. It is therefore important to ascertain 

whether their frequency and extent is changing. An increasing dust-storm incidence could be both a manifestation of and a contributor to global change. 

By analysing long-term meteorological records for a large number of areas (the 

Great Plains of the USA, the USSR, Morocco, The Arabian Gulf, Australia, the 

Sahel-Sudan zone of Africa, China, Mongolia and Mexico) certain conclusions 

can be drawn. The first of these is that there is no one global pattern of dust-storm 

frequency trend. Some stations (e.g. in the Sahel) show a clear upward trend of 

great severity, others show a downward trend (e.g. Mexico City), while others 

show a more cyclical pattern. In many cases it is evident that essentially natural 

processes (precipitation totals, snow cover, wind strength) determine the frequency of dust events in any one year. It has also been possible to show the importance 

of runs of drought years (e.g. in the High Plains in the 1930s, and in the Sahel zone 

of Africa in the 1970s and 1980s). Elsewhere, however, various human activities 

have been significant in determining dust-storm frequency variations: the introduction of centre-pivot irrigation in the High Plains, the abstraction of water from 

the Owens and Mono basins in California, the disruption of surfaces by construction activity and vehicle use (e.g. in Ulan Bator, Mongolia), and the deliberate 

stabilisation of susceptible surfaces (e.g. the Lake Texcoco scheme in Mexico). 

Introduction 

Dust storms have often been regarded as one of the most important manifestations 

of deserfification, and interest in this phenomenon has increased in recent years 

(see Pye, 1987, for a review). As McTainsh (1986) has pointed out, it is important 

to monitor dust-storm events if one is to appreciate the extent of desert degradation. As Table I indicates, dust storms have many environmental consequences, a 

large number of which are adverse. These encompass possible changes at the global 

scale, including suppression of rainfall and substantial nutrient addition to offshore 

areas. 

There are a variety of methods for monitoring dust-storm events, including 

satellite imagery (Middleton et al., 1986), archival information (Bucher, 1986) and 

the analysis of meteorological data (e.g. Goudie, 1983). This last method forms the 

basis of this paper, since it provides the most complete geographical coverage at the 

global scale. Locations are listed in Table II. 

Climatic Change 20: 197-225, 1992. 

9 1992 KluwerAcademic Publishers. Printed in the Netherlands. 
198 A.S. Goudie and N. J. Middleton 

TABLE I: Some environmental consequences and hazards to human populations caused by dust 

storms 

Consequence Example 

A. Environmental 

Soil erosion 

Soil nutrient gain 

Plant nutrient gain 

Salt deposition and groundwater salinisation 

Playa formation and relief inversion 

Sediment input to streams 

Case hardening of rock 

Stone pavement formation 

Desert varnish formation 

Loess formation 

Silcrete development 

Calcrete development 

Climatic change 

Ocean sedimentation 

Glacier Mass budget alteration 

Ventifact sculpture 

Rock polish 

Radiation 

B. Human-related 

Transport disruption 

Disease transmission (human) 

Disease transmission (plants) 

Radioactive-dust transport 

DDT transport 

Air pollution 

Radio communication problems 

Animal suffocation 

Animal madness 

Rainfall acid neutralisation 

Machinery problems 

Warfare 

Closing of business 

Reduction of property values 

Reduction of solar power potential 

Car-ignition failure 

Drinking-water contamination 

Electrical-insulator failure 

Kalma et al. (1988) 

Syers et al. (1969) 

Das (1988) 

Logan (1974) 

Khalaf et al. (1982) 

Goudie (1978) 

Conca and Rossman (1982) 

McFadden et al. (1987) 

Dorn (1986) 

Liu et al. (1981) 

Summerfield (1983) 

Coud~-Gaussen and Rognon (1988) 

Maley (1982) 

Rea and Leinen (1988) 

Davitaya (1969) 

Whitney and Dietrich (1973) 

Lancaster (1984) 

Coakley and Cess (1985) 

Houseman (1961) 

Leathers (1981) 

Clafin et aL (1973) 

Becket (1986) 

Riesborough et aL (1968) 

Hagen and Woodruff (1973) 

Martin (1937) 

Choun (1936) 

Saint-Amand et aL (1986) 

L6ye-Pilot et al. (1986) 

Hilling (1969) 

Agence France Press (1985) 

Gillette (1981) 

Gillette (1981) 

Reinking et aL (1975) 

Clements et al. (1963) 

Clements et al. (1963) 

Kes (1983) 

The following terms can be used to define the miscellaneous types of dust event 

caused by aeolian processes: 

a. Dust storms are the result of turbulent wind systems entraining particles of 

dust into the air, so that visibility is reduced to below 1000 m. Examination of 

humidity data may differentiate visibility reduction resulting from wind from that 

resulting from fog. 

Climatic Change March 1992 
The Changing Frequency of Dust Storms Through Time 199 

TABLE II: Locations of meteorological stations for which long-term 

dust-event records are presented 

Dodge City (Kansas, USA) 37 ~ 42'N 100 ~ 0'W 

Big Spring (Texas, USA) 32 ~ 10'N 101 ~ 25'W 

Lubbock (Texas, USA) 33 ~ 40'N 101 ~ 53'W 

Mexico City (Mexico) 19 ~ 20'N 99 ~ 10'W 

Ouarzazate (Morocco) 30 ~ 55'N 6 ~ 50'W 

Marrakech (Morocco) 31~ 9'N 8 ~ 0' W 

Potsikum (Nigeria) 11~ 39' N 11~ 2' E 

Maiduguri (Nigeria) 12 ~ 0"N 13 ~ 20'E 

Sokoto (Nigeria) 13~ 2' N 5~ 15" E 

Nouakchott (Mauritania) 18 ~ 9"N 15 ~ 58'W 

Dakar (Senegal) 14 ~ 34' N 17 ~ 29' W 

E1 Fasher (Sudan) 13 ~ 33'N 25 ~ 26'E 

E10beid (Sudan) 13 ~ 8'N 30 ~ 10'E 

Khartoum (Sudan) 15 ~ 31'N 32 ~ 35'E 

Kuwait 29 ~ 30"N 47 ~ 30'E 

Bahrain 26 ~ 0'N 50 ~ 35'E 

Doha 25 ~ 15'N 51 ~ 35'E 

Aqaba (Jordan) 29 ~ 13'N 35 ~ 0'E 

Ma'an (Jordan 30 ~ 12'N 35 ~ 44'E 

H4 (Jordan) 32 ~ 30'N 38 ~ 12'E 

H5 (Jordan) 32 ~ 12'N 37 ~ 8"E 

Shobak (Jordan) 30 ~ 32'N 35 ~ 33'E 

Hotien (China) 37 ~ 25'N 79 ~ 55'E 

Minqin (China) 38 ~ 41'N 103 ~ ll'E 

Ulan Bator (Mongolia) 47 ~ 54"N 106 ~ 52'E 

Zamiin-Und (Mongolia) 43 ~ 44' N 111 ~ 54' E 

Choibalsan (Mongolia) 48 ~ 04'N 114 ~ 30'E 

Onslow (Australia) 21 ~ 40' S 115 ~ 12'E 

Alice Springs (Australia) 23 ~ 40'S 133 ~ 50'E 

Mildura (Australia) 34 ~ 13'S 142 ~ 9'E 

b. Dust haze consists of aeolian dust particles suspended in the air, which are 

not actively being entrained and which have been raised from the ground by a dust 

event that occurred prior to the time of observation or at a considerable distance 

away. Visibility may sometimes be reduced to less than 1000 m, but is frequently 

more than that. 

c. Blowing dust is the state where dust is raised above the ground locally, but 

does not reduce visibility at eye level to less than 1000 m. 

d. Dust devils or dust whirls are local, spatially limited, columns of dust that 

neither travel far nor last long. 

The Great Plains of the USA 

The Dust Bowl of the 1930s is perhaps the best-known and most oft-quoted example of large-scale wind erosion and dust-storm activity anywhere in the world. The 

core of the dust bowl area comprised the western third of Kansas, south-east 

Colorado, the Oklahoma Panhandle, the northern two-thirds of the Texas PanClimatic Change March 1992 
200 A.S. Goudie and N. J. Middleton 

handle and north-east New Mexico, although most of the Great Plains experienced 

dust-bowl conditions at some time during the 1930s. Indeed some of the worst 

conditions were found as far north as Wyoming, Nebraska and the Dakotas. 

The most severe dust storms ('black blizzards') occurred in the Dust Bowl between 1933 and 1938, with activity being at a maximum during the spring of these 

years. At Amarillo, Texas, at the height of the period, one month had 23 days with 

at least ten hours of airborne dust, and one in five storms had zero visibility 

(Choun, 1936). For comparison, the long-term average for this part of Texas is just 

six dust storms a year (Changery, 1983). 

The reasons for this most dramatic of ecological disasters have been widely discussed, and blame has largely been laid at the feet of the pioneering farmers and 

'sod busters' who ploughed up the plains for cultivation. For although dust storms 

are frequent in the area during dry years, and the 1930s was a period of drought, 

the scale and extent of the 1930s events were unprecedented (Figure l(a)). 

The waves of settlers that arrived in the area from 1914 to 1930, in conjunction 

with the inceasing use of mechanised agriculture, catalysed by high wheat prices, 

led to exceptionally large-scale wind erosion when drought hit the plains in 1931. 

In 1937 the US Soil Conservation Service estimated that 43% of a 6.5 million ha 

area in the heart of the Dust Bowl had been seriously damaged by wind erosion. 

One event, which raised material in Montana and Wyoming on 9 May, 1934, carried an estimated 350 million tons of soil eastward, depositing dust in Boston and 

New York in the morning of 11 May, and on ships' decks 500 km out in the Atlantic during the next day or so (Worster, 1979). 

An approximate 22-yr drought cycle has been identified in the Western United 

States (Mitchell et al., 1979). Major droughts have occurred in the Great Plains in 

the 1890s, 1910s, 1930s, 1950s and 1970s, and these droughts are normally 

periods of exaggerated dust-storm activity (Figure l(b)). Soil loss in the 1970s was 

on a scale comparable to that of the 1930s (Lockeretz, 1978). This is significant for, 

as Gillette and Hanson (1989) observe, the early 1970s was not a period when 

cumulative departures from normal rainfall were as marked as they had been in the 

1930s and 1950s in the Great Plains. Thus other factors such as the occurrence of 

strong, erosive wind storms may be as important a causative factor as simple lack of 

rainfall. 

Above all, in the 1970s the consequences of a new phase of inappropriate cultivation practices became apparent. Perhaps the worst single dust storm occurred 

after two years of drought, in the Portales Valley area of eastern New Mexico, as a 

low pressure frontal system moved eastwards across the Great Plains on 23 

February, 1977. In the Portales Valley dryland wheat farming had moved onto marginal land as a result of economic factors and high-technology land-use practices. 

In addition, certain government policies reduced the disincentives to cultivate marginal land - the Wheat Disaster Assistance Program compensated farmers for loss 

of crops to wind erosion. Thus, cultivation of wheat took place on marginal lands, 

some of which were highly susceptible relict Holocene or late Pleistocene dune 

Climatic Change March 1992 
The Changing Frequency of Dust Storms Through Time 201 

s 

120 

100 

80 

60 

2O 

0 

I 

1920 1930 

[3 Dodge City 

O Big Spring 

I 1940 l&O 1960' 19'70 

Year 

b 500 - 

400 

.~ 300 

"5 

o 200 

J= 

lOO 

i [ i i i i i i r , , i i i i i i i i i i i i i i i i i i i i i i i i i i 

1950-51 1960-61 1970-71 1980-81 

Fig. 1.(a) Frequency of dust-storm days at Dodge City, Kansas (1922-61), and for Big Spring, Texas 

(1953-70) (after Gillette and Hanson, 1989). (b) Yearly total hours of blowing dust for Lubbock, 

Texas (summing August through July of the following year, after Wigner and Peterson, 1987). 

fields and loess. This extension of the agricultural area was encouraged by the high 

prices that followed export sales of great quantities of wheat to the USSR in 1975. 

These crops were irrigated by center-pivot irrigation, which requires the removal of 

linear wind breaks made up of trees planted since the Dust Bowl era to help prevent wind erosion (McCauley et al., 1981). Some farmers ploughed their fields 

parallel to rather than transverse to the erosive wind direction, and some had failed 

Climatic Change March 1992 
202 A.S. Goudie and N. J. Middleton 

to leave a protective cover of stubble mulch on their fields. The dust palls from Portales Valley and an area in eastern Colorado/western Kansas were tracked on 

SMS-2 and GOES-1 satellite imagery southeastwards, obscuring 400 000 km 2 of 

ground surface in the south central USA and out over the mid-Atlantic Ocean 

(Breed and McCauley, 1986). 

Other Areas of the USA 

One area in the USA where allegedly increasing dust-storm activity is occurring 

and causing concern is in the Owens and Mono valleys of California. Here local 

consumption of water and longer distance inter-basin transfers are desiccating 

Owens and Mono lakes (Cahill, 1984). Dust storms deflate saline materials from 

the drying lake floors. 

A variety of factors operate to cause local increases in dustiness in other parts of 

the American south west. Nakata et al. (1981) documented numerous ways in 

which human activity had destroyed the stability of desert surfaces, producing dust 

plumes when Santa Ana winds blew in January 1973. Such activities included road 

building, agriculture, urban development, stream channel modification and offroad-vehicle use. In Arizona, where dust storms cause numerous road accidents 

along interstate routes 8 and 10, cool-air downdrafts from summer thunderstorms 

raise loose material largely from abandoned, sparsely vegetated farm fields (Hyers 

and Marcus, 1981). 

Mexico 

A study by Jauregui (1960) of dust storms at Tacubaya in Mexico City over the 

period 1923-58 shows a marked interannual variability in frequency, but with no 

trend over the period. Jauregui points out in another paper (1969) that dust-storm 

intensities are generally lower at Tacubaya than at the airport on the northeast edge 

of the urban area, but as Jauregui's data (1960) for Tacubaya have no apparent visibility limit itis impossible to compare his frequencies with those taken from the airport. Nevertheless, he found no trend in dust-storm frequency from 1923 to 1958, 

whereas a marked downward trend in frequency is apparent for all visibility classes 

used in the data from the airport over the period 1952-83 (Figure 2). This decrease in frequency can be explained with reference to three major factors. 

1. Rainfall 

A gradual increase in rainfall in Mexico City over the data period (Figure 2) is 

shown for precipitation figures from Tacubaya. A similar steady increase has been 

noted for the station at San Juan Aragon, about 7 km north-north-west of the airport and on the same side of the urban area, annual rainfall totals here being of the 

order of 200 mm less than those at Tacubaya (Janregui and Klaus, 1982). Jauregui 

Climatic Change March 1992 
The Changing Frequency of Dust Storms Through Time 203 

Rainfall 

..... Dust days (visibility < 5OOOrn) 

...... Dust days (visibility < 1600m) 

-- Dust days (visibility < lO00m) 

1200 - 

- A^ 1000 - 

wVVW 

600 - I ' ' ' ' " " - 60 V, Y ! -: ,%: 

4oo4'--, I \ ?,; \ -4o 

>, [ '~ ,, ~ l l ! 9 $ 

2O0-] z'~ /\ -x ,/'~ -20 .~ 

~\. 

1952 1955 1960 1965 1970 1975 1980 1984 

Fig. 2. Annual rainfall totals and dust-day frequencies for Mexico International Airport (1952-84). 

(1960) found little correlation between one or two year's rainfall and the following 

year's dust-storm frequency, so that a year or two of low rainfall did not necessarily 

result in a high number of dust storms the following year. For the data period 

analysed at the airport correlations with antecedent annual rainfall were also poor. 

Comparing annual dust-event frequency (visibility <5000 m) with the previous 

year's rainfall produced a Spearman's rank correlation coefficient of -0.14 (56% 

probability of a relationship)and a correlation with the average annual rainfall over 

the preceeding three years was also poor: r= -0.22 with 23% probability. Nevertheless, a gradual increase in rainfall can reasonably be expected to hffve had some 

effect on a concomitant decline in dust-storm frequency over the same period when 

considered with the other factors outlined below. 

2. Urban Development 

The growth and spread of the urban area around the airport may also have had 

some impact on dust-storm activity. Although perhaps in the short term urban 

sprawl may act to further destabilize dust sources during phases of construction, 

the encroachment of the urban area around the airport that has occurred since the 

1950s will have acted to protect susceptible soil surfaces after the initial stages 

(Jauregui, 1989). 

3. Proyecto Lago Texcoco 

The identification of the dried bed of Lake Texcoco as a major source of dust 

storms resulted in the initiation of a project in 1972 that aimed to stabilize this area. 

Lake Texcoco, at low levels during dry years, has been a source of dust storms over 

Climatic Change March 1992 
204 A.S. Goudie and N. J. Middleton 

Mexico City for at least 100 years (Jauregui, 1960), but drainage for industry, agriculture and human use resulted in the lake's complete desiccation in the early 

1950s. During this decade the lake, situated immediately north-east of the present 

airport, became a major source of dust storms over the airport itself and the city. 

The project has planted pastures of zacate salado (Distichlis spicata), irrigated with 

recycled urban waste water (agua negra) and constructed a number of reservoirs on 

the former lake bed. In 1971 the area accounted for 40% of Mexico City's dust 

storms (SARH 1985); that percentage was reduced to zero by 1984. 

It is interesting to note that the average annual number of dust-storm days occurring at Mexico City shown in the present study is very much less than that quoted 

by Jauregui (1973) and subsequently referred to in a number of more general texts 

on dust storms (e.g. Goudie, 1978; Coudt-Gaussen, 1984a). The value used here is 

4.5 days a year. Jauregui's (1973) value of 68 is quoted from a previous paper 

(Jauregui, 1960), which, as noted above, uses no visibility limit in the dust-storm 

data. Further, Jauregui (1973) uses the value 68 as the average number of dust 

storms, whereas in the original paper (1960) he shows an average 68 dust-storm 

days. This example serves as a useful illustration of the problems and dangers of 

definition and data usage. 

Morocco 

Discussion of dust data for this country is based on new analysis of information 

provided by the Direction de la Mtttorologie Nationale, Royaume du Maroc. Data 

for Ouarzazate, situated on the headwaters of the Dra, south-east of the High Atlas 

in an area of Miocene deposits, show an annual average of 4.1 dust-storm days with 

annual average rainfall of 119 nun (Figure 3(a)). The annual variation in frequency 

of dust-storm days from 1951 to 1980 shows a distinct peak in activity from 1970 

to 1975. Although rainfall was below average in 1971, 1973, 1974 and 1975, other 

periods Of below-average rainfall in the 1960s produced less-remarkable peaks in 

dust-storm activity. The reasons for the generally weak relationship between rainfall and dust-raising in this area are unclear and need further investigation. 

North of the High Atlas, Marrakech is the only other Moroccan station for 

which recent data are available where significant dust-raising occurs (Figure 3(b)). 

The annual average number of days is 5.0. The interannual variation (1951-80) 

shows a distinct peak from 1952 to 1955, reflecting low rainfall in the period 

1951-55. A minor peak in dust-storm activity in 1961/62 seems to be related to 

rainfall of about half the annual average in 1961, and a decreasing trend in rainfall 

from 1972 to 1980 is mirrored to an extent by a minor rise in dust storms over the 

same period after generally higher rainfall and minimal dust storm activity from 

1963 to 1971. 

Climatic Change March 1992 
~- ~E~,~ 

0 = 

"7 

~'= 

tm 

~ 

o o 

/I 

(// 

( 

~. \ ~ I 

......... year per days storm Dust ~'- 

0m 

.< 

,m < 

-- (mm} year per Rainfall 

Mh 

I 

Do ~ 

('3 

........ year per days storm Dust ~ 

Q o o 

I I I I I 

i I 

~ ~ o 

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~\\ - > 

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.......... Days Storm Dust 

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....... days Duststorm 

~ ,aU!.6UU~IJ e.~ a~'UdnL, y.u U ~n 3, ~ua.~u~ ~l,aHu.4q~L eu~!j~ bOG 
206 A.S. Goudie and~N. J. Middleton 

Sahel-Sudan Zone 

Bertrand et al. (1979) show the variation in annual numbers of days with dust haze 

from 1947 to 1978 at Bilma, Zinder and Niamey, although no visibility limit is indicated for their data. At Bilma the number of hazy days rose steadily from 20-30 in 

1955 to more than 200 in 1973. At Zinder and Niamey a rising trend is discernable from the mid-1960s. A't all three stations a significant rise is indicated in 

1968/69. Investigation of rainfall at Niamey, Zinder and Agadez shows that the 

period of significantly increased dust haze accompanies a period of pluviometric 

shortage. The linear correlation coefficient between rainfall at Agadez and days 

with dust haze at Bilma is -0.65; this becomes -0.88 if dust haze is correlated with 

the rainfall of the preceding three years. 

These stations are in the area affected by the Harmattan dust haze. Further 

south and west the evolution of dust haze at Bobo-Dioulasso (Burkina) and 

Bouak6 (Ivory Coast) is estimated by the number of hours of visibility reduced to 

less than 5 km and 10 km for two periods: 1957-69 and 1970-74. At BoboDioulasso the average number of hours of dust haze at these visibilities increased 

by a factor of between 3.0 and 4.5 between the two periods, and between 2.0 and 

2.5 at Bouakt. The seasonality of dust haze was also modified. Dust haze tended to 

appear earlier in the season and finish later, and the months of maximum activity 

changed from February at Bobo-Dioulasso for 1957-69 to December in 1970-74. 

Further evidence from Niger is presented by Heusch (1980). At Tahoua, in the 

AderDutchi massif, the mean annual number of hazy days for the period 1965-74 

was 54, but the frequency varied from nine days in 1965 to an average of 82 days a 

year from 1971 to 1973. 

In northern Nigeria, hazy days with visibility <3000 m at Samaru generally 

increased as rainfall declined from 1962 to 1973 (Adetunji et aL, 1979), and observations of severe dust haze (visibility < 1000 m) at three-hourly intervals at four 

stations during the period 1970-76 showed a marked increase in frequency in 

1972 and 1973 when the drought was particularly severe (Kalu, 1982). Also in 

Nigeria, Adefolalu (1984) shows that the highest numbers of cases of respiratory 

problems associated with dust were recorded during the drought spell 1970-75, 

and the effects of Harmattan dust on human health in Nigeria has been on the 

increase since 1976, and may become serious in the immediate future in southern 

parts of the country which have hitherto been little affected. 

The unusual strength of the Harmattan in recent years is also suggested by 

reports that in 1983 dust reached Libreville, the capital of Gabon, a few kilometres 

north of the Equator, for the first time in 25 years (Morrison 1983). More detailed 

analysis of the transport and Harmattan wind strength needs to be undertaken. 

The above evidence from the literature on the Sahel drought refers to the part of 

the region affected by the dust source of the Chad Basin. 

Data for Nigeria were obtained from the Nigerian Meteorological Department 

for eight stations mainly in the north of the country. These data, which are shown in 

Climatic Change March 1992 
I 

z~ 

~o 

o. o 

0 

s 

v' 

"-4 

E~ 

0 

s 

= 

~ 5 

0 

0.., 

u~Hj aHr, qU ,~our, H~ 1 6(~0 

lO00m) < (visibility 

CO to ~ 0 

I I I 

I 

d I 1 I tl_ 

"4 

~ "22 ; 

ol 

haze dust thick with days of Number 

year per lO00m) 9 Ivisibility 

lO00m) < (visibility 

I ~ I >. 

O" 

> 

o o o o o 

I I I I I 

I L -'-':'- 

~,- = ,= z ~ -,-- 

haze dust thick with days of Number 

year per lO00m) < ',visibility 

~O00m)" < IvJ$ibility 

7 : >~ 

li J : 

ii ii{ 

~o 

haze dust thick with days of Number 

year per lO00m) < (visibility 
208 A.S. Goudie and N. J. Middleton 

Figure 4, indicate the variation in annual totals of severe dust haze days (visibility 

< 1000 m) and rainfall for the period 1955-79 and the average monthly dust day 

totals for two periods: 1955-65 and 1969-79, with the change in average annual 

rainfall between the two periods. Several stations are lacking data for 1966, 1967 

and 1968, when civil war disrupted normal life in Nigeria (Figure 4). 

All stations show a period of decreased rainfall at some time during the late 

1960s/early 1970s, a relative recovery in rainfall totals in 1974 and 1975, with 

some stations experiencing a second low rainfall period in 1976 and 1977. At 

Sokoto this rainfall pattern is mirrored by an upward phase in the number of dust 

days recorded, that falls off again as rainfall rose in 1974/75. At this station the 

average monthly totals of dust days for the two periods do not greatly differ, 

although average rainfall totals were significantly lower during the second, or 

drought, period (1969-79). 

The pattern is somewhat different at Maiduguri to the east of the country. An 

increase in the number of dust days during the early 1970s is clear, and the frequency of dust haze remains generally high after this time despite the relative 

recovery in rainfall totals during the mid-1970s. Thus, for Maiduguri the average 

number of dust days during 1969-79 is significantly greater than in 1955-65, by a 

factor of two for the maximum month. 

At Potiskum, high dust-haze day frequencies for 1970-76 do not show any 

obvious correlations with corresponding annual rainfall, and dust frequency falls 

sharply in 1978/79. Thus, average monthly dust-haze days are just slightly increased during 1969-79 as compared to 1955-65. 

It should be noted that since the dust haze at Nigerian stations is caused by 

material entrained to the north-east and blown by the Harmattan, the local rainfall 

totals are not directly related to dust haze, except by the amount of wash-out they 

represent. Thus, the relationship between dust haze and local rainfall is not a simple one, and although the general deficiency in rainfall totals from about 1968 

occurred throughout the Sahel, the station in Nigeria furthest from the dust source 

- Potiskum - does not show such obvious pluviometric control on the number of 

dust-haze days. At Sokoto and Maiduguri the year-to-year variations in rainfall are 

more closely related to the variation in days with dust haze. Although the relationship between rainfall deficiency and dust-haze frequency is not always obvious or 

consistent at stations in Nigeria, all stations analysed show some degree of increased dust-haze frequency during the period of the first ten years or so of the 

1970s Sahel drought. Another interesting aspect of Nigerian dust-storm activity at 

both Potiskum and Sokoto is that in the later period dust storms tend to occur earlier in the season. 

Data from Mauritania were supplied by the Service M~tdorologique, Nouakchott, and for Senegal by the Agence pour la Sdcurit6 de la Navigation Aerienne en 

Afrique et h Madagascar (ASECNA), Dakar. The variation in frequency of annual 

dust-storm days and annual rainfall totals for Nouakchott is shown in Figure 5. The 

increase in dust-storm days after 1968 is dramatic. Low rainfall totals of 48.1 mm 

Climatic Change March 1992 
The Changing Frequency of Dust Storms Through Time 209 

g 

e~ 

o~ 

CE 

220 

200 

180 

160 

140 

120 

1 O0 

80 

60 

40 

20 

0 

1960 

I I I I 

1965 1970 

-- Rainfall 

.... Dust storm days 

~ ,,\ [-- 90 

- 80 

- 70 

- 60 

50 $ 

- 40 cl 

-30 -~ 

-20 E 

o 

-10 

0 rn 

1980 1985 1986 

J I 

1975 

Fig. 5. Annual frequency of dust-storm days and annual rainfall for Nouakchott, Mauritania, 

1960-86. 

in 1970 and 17.9 mm in 1971 represented just 32 and 12%, respectively, of the 

1949-67 average, and can be seen as the main onset of the drought. The number of 

dust-storm days increased markedly from 6 in 1970 to 65 in 1974 before a reasonably high annual rainfall of 190.6 mm in 1975; dust-storm activity declined to 

25 days in 1976 and 27 days in 1977. In 1977, however, the rainy season brought 

just 2.7 mm of precipitation, making it the driest year since records began in 1931, 

and dust-storm activity rose to 55 and 61 days in 1978 and 1979, respectively. The 

total dropped to 33 dust-storm days in 1980 after a relatively heavy rainfall in 

1979, but rose to an unprecendented 85 days in 1983 and remained at around 

80 days per year until 1986. 

At Nouakchott, further investigation of the dust storm/rainfall relationship has 

been undertaken using linear-correlation techniques (Middleton, 1987). The 

linear-correlation coefficient between dust-storm frequency and the previous year's 

rainfall (note that the dust-storm season at Nouakchott is primarily in the first six 

months of the year, before the onset of the rainy season) is -0.53 (28% explanation). The relationship between dust storms and antecedent rainfall is stronger, 

however, when annual dust-storm days are compared to the average annual rainfall 

over the previous three years (linear-correlation coefficient = -0.75, with 56% 

explanation). This fairly strong relationship is similar to that found by Bertrand et 

al. (1979) for Agadez and Bilma in Niger. 

In Senegal, dust haze from the more arid areas to the north and east is more 

common than dust storms generated locally. Data for annual frequencies of dust 

haze and rainfall at Dakar are shown in Figure 6. Fairly closely related trends in 

these two parameters are apparent. Low rainfall in 1968 marks the beginning of an 

increasing trend in the numbers of dust-haze days, peaking in 1970 and staying 

Climatic Change March 1992 
210 A.S. Goudie and N. J. Middleton 

60 

9oo 

8OO 7oo A 

600 -~ 

i 

400 -- 

3oo /~ 

! 

~ 200 ~ 

~ lOO 

9 ~0 I 

-- Rainfall 

------ Dust haze 

Data: ASECNA, Senegal 

I ~" ,,~ 

I \ 

, 

J 

II 50 

I I 

i I 

i I 

f I 

i I 

I I , 40 

I I / 

I |1 

f r 

I 30 

III 20 

z 

I I I I I I I I i I I 0 

1966 1968 1970 1972 1974 1976 19781979 

Fig. 6. Annual rainfall totals and frequency of dust-haze days at Dakar, Senegal (1966-79). 

high while rainfall was low, until a relative recovery in rainfall in the period 1973- 

75, during which time dust-haze days declined in frequency. After 1975 rainfall 

again declined, with a concomitant increase in dust haze. 

In Mali, where the River Niger sank to its lowest recorded level in 1984, data 

were unavailable, but reports in the newsmedia attest to the increase in dust haze 

and storms that has occurred since the onset of the recent drought: 

... every hour of every day of the week I spent in Mall... a giant dust cloud hung in the air, covering the 

country. It was Mali's precious topsoil, turning into its shroud. (Lean, 1985, p. 14) 

Data from the Sudan were taken from the Sudan Meteorological Department 

Annual Meteorological Reports, with some additional material supplied direct 

from the department itself. The data refer to five stations across the Sudanese 

Sahel. Data in the yearbooks are given as monthly frequencies of dust storms 

recorded at 0600, 1200 and 1800 GMT, so that a record of an event at 0600 and at 

1200 may refer to a single storm that lasted for six hours or more, or to two 

separate events. Thus, the graphs in Figure 7 show annual rainfall totals with 

annual totals of recorded dust events (i.e. the summation of frequencies for 0600, 

1200 and 1800 GMT). From 1975 most Sudanese stations started making an extra 

visibility reading at 0000 GMT, and some of the data presented below have been 

published without taking this additional observation into account (see Middleton, 

Climatic Change March 1992 
The Changing Frequency of Dust Storms Through Time 211 

a EL FASHER 

700 

680 

500 

488 / 

300 

~- 208 

g 

lOO - 

b EL OBEID 

700 ~ O 

1950 

680 

500 ~ Rainfall 

.... Dust storms 

300 

_ 

2DO " \,/ :',,i -4.~; !t) ~176 

-- Rainfall 

---- I Dust storms 

i 

I 

I 

I 

I / 

E.'~ I 

/ ~ V t 't/ 

I ~ II 

11 7 

10 

8 

I 

il 6 

5 

4 ~ 

3 

r Ill \~i i ~ #1 I i\" I t I I I 0 ~ 

1954 19158 19162 1968 1970 19174 19178 1882 1983 

-- Rainfall C KHARTOUM 

400 - ----~ Dust storms I\ 

I 

.o_ ^A '", / 

i 

~1oo ,~v i k!v W v ,.~ . 

I ~'- / % ~- / I 4 I I! I~' 

"# % / "7 I // % I I f 

8 , "~ ', , r ,~ , 4 ........ 

1956 1954 1958 1962 1966 1970 1974 1978 1982 

Fig. 7. Annual rainfall totals and dust-storm frequencies for Sudan: (a) E1 Fasher (1950-83); 

Obeid (1950-78); and (c) Khartoum (1950-83). 

29 

1 

Ii 24 

II 

I I 22 

/ 16 

14 

8 

. ~g 

2 "~ o 

1983 

(b) El 

1985a, Hulme 1985; Middleton, 1985b). Some of these data, therefore, were inflated - those for E1 Fasher, E10beid and Khartoum - but those for Aroma and 

Tokar were unaffected by the extra reading. Nevertheless, the general trends indicated in Middleton (1985a) are still evident in the adjusted data used in Figure 7 

Climatic Change March 1992 
212 A.S. Goudie and N. J. Middleton 

(omitting the 0000 GMT reading, thus maintaining consistency before and after 

1975). 

The annual dust-storm frequency and annual rainfall totals for E1 Fasher, E1 

Obeid and Khartoum (Figure 7) show a marked rise in dust-storm activity dating 

from the late 1960s/early 1970s. Particularly low rainfall in 1972 and 1973 at E1 

Fasher, for example, was followed by a distinct rise in dust-storm frequency, 

peaking in 1974, falling in 1975 and 1976 after high rainfall in 1974, but remaining 

at increasing levels after that year as annual rainfall remained for the most part 

below 200 ram. The zero dust-storm reading for 1979 followed the wettest year in 

the central Sudan (1978) in the last 20-25 yr (Trilsbach and Hulme, 1984), 

although particularly high rainfall was not evident at E1 Fasher itself. 

The data that have been presented for the Sahel-Sudan belt of Africa show a 

considerable degree of homogeneity. In particular there is evidence for clear 

increases in frequency at many stations, and there is a relationship between this 

trend and a regional rainfall decline since the mid- and late 1960s. This increase in 

dust frequency led to increases in dust loadings in the Caribbean, as noted by Prospero and Nees (1977 and 1986). 

The Middle East 

Some data covering a sufficiently long period were available for three stations 

located in the area largely affected by the Shamal dust flow. Figure 8 shows the 

variation in annual numbers of days with visibility obscured to < 1000 m by dust at 

Kuwait (1962-84), Bahrain (1946-83) and Doha (1962-83). The graphs seem to 

indicate a gradual decline in frequency at Bahrain and Doha, though the length of 

record at Doha is inadequate for drawing firm conclusions. It should be remembered, however, that in these readings there is no distinction made between dust 

raised locally and that advected from other areas (largely from northern Saudi 

Arabia and southern Iraq in these two cases), so that it is impossible, from these 

data alone, to draw any conclusions as to possible decreasing dust-storm frequency 

on either the west coast of the Arabian Gulf or the lower Mesopotamian Plain. 

Indeed, at Kuwait, nearer to the northern sources, but also affected by local dustraising, no trend is discernable. Nevertheless, it is worth noting that in south-east 

Iraq some large areas on the Iranian border were flooded during the Iran/Iraq war, 

which may reduce Shamal dust loads in future. 

Data from five stations in the Hashemite Kingdom of Jordan (not previously 

published) showed few discernable trends for individual sites, but when annual 

totals of precipitation and dust or sand storms were summed for all five stations for 

the period 1965-1988 Figure 9 was produced. Deflation is strongest during spring 

and autumn months in this part of the Middle East, when frontal cyclones from the 

Mediterranean and North Africa track eastwards across the country (Middleton, 

1986). These systems are also the most important for bringing precipitation to 

Jordan, and this is borne out by the increasing trend of precipitation and deflational 

Climatic Change March 1992 
The Changing Frequency of Dust Storms Through Time 213 

vt 

x: 

@ 

"5 

40 i 

30-- 

20 

10 -- 

0 

1962 

KUWAIT INTERNATIONAL AIRPORT 

1962-1984 x = 27.0 

i F I I I I I p , n I J I I I I I I I 

1966 1970 1974 "f978 1982 1984 

.• 18 -- BAHRAIN INTERNATIONAL AIRPORT 

9 -~ 16 - 1946-1983 T~ = 5.5 

g 

o ~14 

v/ 

>, 12 

10- 'g 

xz 

6- 

@ 

"6 2- 

O i i i i , ~ t i t i i i i i i i i 

1946 1960 1960 1970 1980 i983 

-~ 18- A DOHA INTERNATIONAL AIRPORT, QATAR 

oE 16 - / I 1962-1983 ~ = 6.6 

o 14-- 

w 

12-- 

10-- 'T= 

8 

~, 4- 

"6 2- 

0 i r i i , i i i i i e i i i i i i i [ i i , i i i i r i 17 

1962 1970 1980 1983 

( ~" = Average numl)er of days per annum with visibility ~< lO00m in dust) 

Fig. 8. Annual frequencies of days with visibility less than 1000 m because of dust at Kuwait, Bahrain 

and Doha. 

Climatic Change March 1992 
214 A.S. Goudie and N. J. Middleton 

1000 - 

800 - 

600 - 

400- / 

E 

v ,t/",_/V 

t v ~ ~. /', iv "" ' \ +- \ \ / \ 200 ~ V ~l \ J 

& 10~ 1 tz 

~- I I i i i I i I i I I I i I I I I I I I 

-110 

- 100 

- 90 

- 8O I 

I 

# 

- 70 i 

- 60 

- 50 

- 40 

- 30 

-zo 

"5 

-10 

I 0 z 

65 70 75 80 85 90 

Year 

Fig. 9. Annual frequency of dust-storm days and mean annual rainfall for Jordan (1965-1983), based 

on data from Aqaba airport, Ma'an, H4, H5, and Shonbak. 

activity, as indicated by dust or sand storms from the mid-1970s. 

Another factor that has had an effect on atmospheric dust loads, particularly on 

the Arabian Peninsula, is the industrial development that has taken place since the 

mid-1970s. Development of industry and the concomitant expansion of urban 

areas destabilizes desert surfaces, producing increased local dust-raising during the 

construction phases, and once established, industrial pollutants contribute to 

atmospheric dust loadings locally (Behairy et aL, 1985). Although such activities 

are highly localised and often on a small scale with respect to the vast areas of 

desert unaffected by human activities, they become more significant when it is 

remembered that meteorological stations are, for the most part, situated within or 

on the outskirts of settlements. Thus, industrial and construction activities may take 

on a disproportional significance in their local effects on dust events as recorded by 

meteorological observers. 

The USSR 

Two examples of changing dust-storm frequencies can be given for the USSR, and 

both demonstrate the important role played by human activities. The first of these 

relates to the effects of the vegetation removal and ploughing in the 1950s as part 

of the Virgin Lands Scheme. As Table III shows, in the Omsk region dust-storm 

frequency went up on average by two and a half times when one compares the data 

for the period 1936-50 with those for 1951-62. 

More recently, great concern has been expressed about the increasing deflation 

of dust from the desiccating Aral Sea. As the inflow of water into the lake is 

reduced, so the lake floor is exposed and dries out, exposing areas of susceptible 

Climatic Change March 1992 
The Changing Frequency of Dust Storms Through Time 215 

TABLE III: The effects of the Virgin Lands schemes on frequency of dust-storm days in the Omsk 

region of the USSR (after Sapozhnikova, 1973) 

Station Mean annual number of dust-storm days Increase 

1936-1950 1951-1962 

Omsk steppe 7.0 16.0 x 2.3 

Isil'-Kul' 8.0 15.0 x 1.9 

Pokrov-Irtyshsk 4.0 22.0 x 5.5 

Poltavka 9.0 12.0 x 1.3 

Cherlak 6.0 19.0 x 3.2 

Mean 6.8 16.8 x2.5 

materials to deflational attack. These materials include an annual blowoff of 43 

million tonnes of salt (Sdasyuk, 1989). 

China 

Some of the earliest written records of dust-storm activity anywhere in the world 

are recorded in the ancient Chinese literature. They refer to dusffalls in northern 

China, and are variously known as 'dust rain', 'dust fog' or 'yellow fog', usually 

occurring in the spring months. The earliest known record of 'dust rain' was in 1150 

BC, and is found in a historical book: Zhu Shu Ji Nian (Chronicles Recorded on 

Bamboo Slips, quoted in Liu et al., 1981). 

Zhang (1985) used 1156 historical records to show the decadal frequency of 

dust-rain years in China for the period since 300 AD (Figure 10). The periods of 

frequent occurrence are 1060-1090 AD, 1160-1270AD, 1470-1560 AD, 1610- 

1700 AD, and 1820-1890 AD. Comparison of dust-rain years frequency with a 

winter-temperature index for the period 1470-1969 shows that they are in oppog 

10 

8 

2 

0 "~" I I I i i i I I I I 

o ~o ~o ~8 g g g 8 8 8 o ~8 o ~ o ~o ~

Year 

Fig. 10. The frequency curve of dust fall since 300 AD in China (after Zhang, 1985). 

I 

Climatic Change March 1992 
216 A.S. Goudic and N. J. Middleton 

HOTIEN 60 

100 

80 

60 

40 

~ 2o 

~ 0 

1954 

I~ A,, t. A 

I 1 I ~ / ~t / t. l i" 

I I I ~I ~I I ~. 

_l I l ~1 ~ I / ,,, / ~1 t | I 

I I I I I I I I I I I I I I I I I I I I I I I I I 

1960 

50 

40 

30 

.20 ~ 

-10 E 

0 a 

1965 1970 1975 1980 

MINQIN 

Rainfall 

.... Dust storm days 

60 

200 

160 

120 

.,'\/ 

\1 

8O 

40 - 

0 

1954 

I 

I 

! ' ,'~A ;'~ A 

I /~/\~/~ , 

I ,,.I ',1 V I~ I l~ 

/A ), / v '...,,' vV/ 

I ',,/~ 

I I I I I I I I I I I I I I I I I I I I I i I I I 

1960 

50 

40 

30 

2O 

10 E 

0 

0 o 

1965 1970 1975 1980 

Fig. 11. Annual rainfall totals and dust frequencies at (a) Hotien and (b) Minqin, China (1954-80). 

Climatic Changc March 1992 
The Changing Frequency of Dust Storms Through Time 217 

site phase. Although the data set is extensive it is not evident how homogeneous it 

is through time. 

Modern meteorological records for the latter half of this century show that 

Hotien (or Khotan) on the southern margin of the Taklimakan Desert records an 

average of 32.9 dust-storm days a year, with a mean annual rainfall of 35 ram. 

Large-scale dust-raising is caused by frontal passages moving westward, and local 

storms may be produced by katabatic wind flow. The dustiest months are from 

March to June, when 67% of storms occur. The diurnal variation in dust-storm frequency shows that activity occurs throughout the 24-hr period - many turn-of-thecentury travellers crossing the region describe storms lasting for several days - with 

a definite maximum around midday during the most active months. 

The annual variation in dust-storm frequency at Hotien from 1954 to 1980 is 

shown in Figure l l. The interannuai variation is not great (CV = 24%). A gradual 

decline in frequency over this period is discernable, but no increasing trend in rainfall is apparent, and correlations between dust-storm days and annual rainfall were 

found to be poor (linear-correlation coefficient = -0.03). 

The Gansu Corridor (sometimes referred to as the Kansu or Hexi Corridor) is a 

narrow belt of land extending along the northern piedmont of the Qilian Shan 

mountains and bordered to the north by the Longshou Shan mountains. The orientation of the corridor, WNW-ESE, is such that outbreaks of cold polar air, often 

associated with the passage of south-westerly moving frontal systems, are funnelled 

through the corridor causing large-scale dust storms. These 'black storms', which 

occur principally in the spring, cause widespread damage to property in the area. 

Xu et al. (1979) define the black storm in the Gansu Corridor as a gale with wind 

speed > 25 m/s, together with a visibility < 50 m. Dust storms caused by thunderstorm downdrafts may also occur in the corridor (G. L. Wells, pers. comm., 1985). 

The corridor is dry, receiving less than 300 mm of rainfall a year, and the surficial sediments comprise sandy loess in the belt along the south of the corridor and 

alluvial sediments to the north brought from the Longshou ranges. The station of 

Minqin is situated at the eastern end of the corridor and averages 37.3 dust-storm 

days a year, with an annual rainfall of 116 ram. Dust storms largely occur during the 

spring months (63% of all storms are recorded from March to July), while rainfall is 

largely concentrated later in the year, during the summer months. The annual variation in frequency from 1954 to 1980 (Figure 11) shows no particular trend, and the 

interannual variation is not large (CV= 27%). There seems to be a vague relationship between dust-storm frequency and the rainfall of the previous year, and this 

relationship was investigated in more detail but was found to be statistically insignificant. A test of annual dust-storm frequency against average rainfall over the previous three years also showed little relationship (r = -0.03). 

Further investigation of monthly data on dust-storm frequency, temperature and 

rainfall for 15 Chinese stations across the north of the country has been carried out 

by Littmann (in press) using spectral analysis. Spectral energy for these time series 

was mostly concentrated in the wavelength of seasonal variations, but supraClimatic Changc March 1992 
218 A.S. Goudie and N. J. Middleton 

seasonal signals were also identified indicating fluctuations in the range of ENSO 

variability between 3.6 and 5.5 yr with various phase dislocations. Littmann speculates that this interannual variability may be linked to shifts in circumpolar vortex 

dynamics. 

Mongolia 

Time-series data from three stations in the Mongolian People's Republic illustrate 

differing patterns of annual dust-storm frequency variation (Figure 12). 

A rising trend in frequency at Ulan Bator during the late 1970s and early 1980s 

mirrors a declining trend in precipitation totals. Human activity has also had an 

effect, for off-road vehicle use and intense construction activity around the meteorological station on the city's outskirts have had the effect of removing vegetation 

and destabilizing soil surfaces. 

The influence of precipitation totals is also clear at Zamiin-Uud on the Chinese 

border. Low totals in the early 1960s produced intense dust-storm activity culminating in 114 dust-storm events in 1966. The period since the early 1970s, by 

contrast, when precipitation has been relatively high, has reduced dust-storm frequencies to an average of around 20 events. The precipitation signature on annual 

dust-storm frequency at Choibalsan in the north-east is less marked. 

Australia 

The increase in dust-storm activity during dry years in Australia was noted by 

Loewe (1943) for the country as a whole and by Thompson (1982) at Broken Hill. 

This observation is partly confirmed by long-term dust-event frequency data from 

a number of stations from different parts of the country (e.g., Figures 13(a), (b) and 

(c). 

Heathcote (1983), however, suggests that the 1940s was a period of high duststorm activity, indicating that dust from the wind eroded wheatfields of southern 

Australia, coloured the sunsets of the eastern capitals and even reached the snowfields of New Zealand. 

Gibbs (i975) notes that 1973 and 1974 were years of extremely heavy rainfall 

over much of the country, and these years show minimal dust-storm frequencies at 

all stations. Bigg and Turvey (1978) studied the sources of atmospheric particles 

over Australia, sampling from aircraft in October 1974, November 1975 (years of 

high rainfall and low dust-storm activity) and May 1977 (although a drought year, 

during the season of generally low dust-storm activity). Largely as a result of the 

sampling periods, therefore, they concluded that 'the land surface itself is almost 

ineffective in generating particles' (Bigg and Turvey, 1978, p. 1649). 

The drought of 1977 is reflected by minor peaks in dust storms at Alice Springs 

and most of the stations to the south, but not to the north. 

The effect of antecedent rainfall on wet deposition dustfaUs has been studied 

Climatic Change March 1992 
F," 

C~ 

~43 

~3 

,-.~= 

I -- 

~ ~-- ~176176 

~ o, .~ 

~ , ~." 

~ "- 

"::.. 

~.~ ..... 

',~ ., 

~ o~ 

." 

%. 

~" ~. "" 

"~ O) 

.. 

o.,,~ 

I i i 

03{::3 I~ .1~ o} 

o~ Dust Storms per year 

I 

Precipitation per year (ram) 

o 

~ I L _l 

~,- 

o~ 

"w" ! ! , f 7 

0 o 

Dust Storms per year 

Precipitation per year (mm) 

s ~ o ~

o (:3 o 

o 

Cb 

c8 

o~ 

03 

Dus
220 a.s. Goudie and N..I. Middleton 

ONSLOW 

< Dust events 

I 

II 

It ~ I I 

IJ I I 

20 II I I 

I I I I 

1o ; t; 'i / ~ ill t 

,i' ,I" ,~ 

o i ,'G , , , i I i i i i i ! i i i i i ! 

" 1941 t950 1960 

\ 

Dust storms 9 

\ 

\ 1%. 1, \\1 "% 

, , (, v s , 

1970 1975 

AUCE SPRINGS 

< Dust events > < Dust storms 

70 ~ 1% . / /~ 

604 I \\ / 

/ .I \ I 9 I \ 

5o-I t ~ I A / \A 

4o4 x 4 ; t~/\ / "\ 

i ok^ t. ',,/7 t / \ 

i 10 k % 

1941 1950 1960 1970 

- 800 

600 

400 

- 200 

0 

1980 1962 

C MILDURA 

< 

30 

Dust events -- > Dust storms 9 

t 

4 

I I 

, \ 

I , ~ 

tO /'~\ ^ / \ l #~ / 

I. \ / / ~ I \ r',, t~' 1". / 

\ I %/ ~,/ \/; x_ / "~ ,_t ~! ~/" 

8 ('I ................... ~"~ ......... ~-w~. 

01947 1950 1960 1970 * ' ,'?~0 1"352 

Fig. 13. Frequency of dust clays in Australia: (a) Onslow (1941-74); (b) Alice Springs (1941-82); and 

(c) Mildur a (1947-82). 

Climatic Change March 1992 
7"he Changing Frequency of Dust Storms Through Time 

TABLE IV: Rainfall, wet-dust deposition and numbers of dust events at Merbein, 

Victoria (modified after Ht, tton 1980) 

221 

1954 1955 1956 1957 1958 1959 1960 

Rainfall (mm) 280 350 420 240 441) 190 310 

CaCO 3 (kg/ha) 24.5 23.8 i6.5 20.5 24.5 26.8 41.0 

Dust-event days 7 9 I 4 4 13 29 

over a period of six summers by Hutton (1980) at Merbein, just north of Mildura, 

Victoria. Calcium carbonate suspended in the atmosphere is derived from the fine 

calcite particles present in the soils of the area, and the amount deposited per hectare in rain during the summer Was found to be inversely related to the rainfall 

recorded during the two previous springs and winters. Hutton observes that the 

total annual weight of carbonate deposited appears to be independent of the 

amount of rain. However, when the annual totals of dust-event days are examined 

in conjtmction with Hutton's figures (Table IV) the situation becomes clearer. In 

1958, for example, when annual rainfall was at a maximum for the six-year period, 

deposited calcium was below average for the period, which seems to be related to 

the small number of dust-event days (4). In 1960, by contrast, although annual rainfall was over 100 mm lower, the number of dust-event days was much greater (29), 

and consequently the deposition rate was at a maximum for the study period. 

In Australia no simple trend in dust-storm frequencies is evident, and this may 

be the result of there being no clear trend in annual precipitation totals (see, for 

example, Hobbs, 1988). 

Conclusion 

The data which we have assembled in this paper demonstrate that there is no one 

global pattern of dust-storm frequency trend. Some stations show a clear upward 

trend (e.g. those in West Africa), others show a downward trend (e.g. Mexico City), 

while others show a more cyclical pattern. In many cases it is evident that essentially natural processes (precipitation totals, snow cover, wind strength) determine the 

frequency of dust events in any one year. It has also been possible to show the 

importance of runs of drought years (e.g. in the High Plains in the 1930s and in the 

Sahel zone of Africa in the 1970s and 1980s). Elsewhere, however, various human 

activities have been significant in determining dust-storm frequency variations: the 

introduction of centre-pivot irrigation in the High Plains, the abstraction of water 

from the Owens and Mono basins, the disruption of surfaces by construction activity and vehicle use (e.g. in Ulan Bator), and the deliberate stabilisation of susceptible surfaces (e.g. the Lake Texcoco scheme in Mexico). 

Further progress in understanding trends in dust-storm activity requires additional analyses to those presented here. In particular knowledge will be furthered 

Climatic Change March 1992 
222 A.S. Goudie and N. J. Middleton 

by a more thorough study of wind-strength effects and of the sources and paths of 

dust transport. 

Acknowledgements 

The authors would like to thank the following national meteorological agencies, 

who kindly provided data: Australia, Bahrain, China, Kuwait, Mauritania, Mexico, 

Mongolia, Morocco, Nigeria, Qatar and Senegal. 

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