Drought in the Near East

Regardless of the degree of aridity, precipitation variability is considerable in the Near East. Figure 16.2 shows the annual rainfall variations for three stations in different moisture regimes across a considerable annual precipitation gradient (150-1000 mm). It is evident from figure 16.2 that high rainfall variability is not confined to the low rainfall areas of the region. The large amplitude of the variations is typical for the region and predisposes it to drought. The patterns of drought in the region are extremely variable in their spatial and temporal dimensions. Some droughts are severe enough to affect the entire region from Morocco to Iran, and well beyond, into Afghanistan and Tajikistan.

Although droughts can have a regional scale, their effects can be very local. In Syria the drought of 1999 initiated a severe decline in the productivity of the rangelands and barley areas at the steppe margins, which continued for several years. However, the drought had comparatively little effect on the production of wheat and tree crops in the higher rainfall areas, which recovered from 2000 onward. This variability of drought patterns at

Year

Figure 16.2 Precipitation for three stations in Syria and Turkey located in different moisture zones.

Year

Figure 16.2 Precipitation for three stations in Syria and Turkey located in different moisture zones.

the local level is illustrated in figure 16.3. It shows the cumulative rainfall deviations for Aleppo, Damascus, and Palmyra in Syria, three locations less than 200 km apart but with different patterns of longer term positive or negative anomalies.

Throughout the region, drought can strike at any time of the growing season. Early-season, mid-season, and late-season droughts are all possible. Table 16.3 shows the occurrences of severe and mild droughts within the growing season at Tel Hadya, Syria, for the 1978-2001 period. For this particular example, a severe drought is defined as a precipitation total of less than 50% of the long-term average, and a mild drought as 50-70% of the long-term average. The periods considered are November-December (the early season), January-February (the mid-season), and March-April (the late season).

Causes of Drought Occurrence

The causes of drought in the Near East are complex, attributed to the geographical extent and exposure to different oceanic/continental influences and the wind systems in the western versus eastern parts of the region.

In North Africa, climate is still poorly understood. According to Ward et al. (1999), most of the precipitation is generated as a result of depressions, which are steered southward from the North Atlantic during soo soo

•300 -,-1---,-,-1-1-.-1-r—i-1-1-1-.-1-1-1-1-1-------.-1-1-!-.-.-

1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1961 1963 1965

Figure 16.3 Cumulative deviations of annual precipitation for three locations in Syria.

•300 -,-1---,-,-1-1-.-1-r—i-1-1-1-.-1-1-1-1-1-------.-1-1-!-.-.-

1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1961 1963 1965

Figure 16.3 Cumulative deviations of annual precipitation for three locations in Syria.

blocking episodes by mid-latitude high-pressure cells. The strength of the blocking is, to a large extent, linked with the North Atlantic Oscillation (NAO; Lamb and Peppler, 1987), a large-scale mode of climate variability in the Northern Hemisphere at monthly, seasonal, interannual, and decadal timescales. According to Hurrell (1995), the NAO is the dominant mode of interannual-decadal climate variability for the Atlantic sector, accounting for 20-60% of the variance over the last 150 years. A simple index of the NAO is the sea-level air pressure difference between the Azores, an island group in the Atlantic Ocean at about 38° northern latitude, and Iceland. A positive NAO phase is characterized by the strengthened westerly winds across the mid-latitude North Atlantic, leading to mild and relatively wet winters in northern Europe (van Loon and Rogers, 1978) but to anomalously dry conditions in the Iberian Peninsula (Zorita et al., 1992) and the Maghreb countries (Lamb and Peppler, 1987). A negative NAO tends to be linked with moist air in the Mediterranean and cold air in northern Europe. The NAO index varies from year to year but tends to remain in one phase for intervals lasting several years. Since the late 1970s, the winter NAO index tends to be positive (Hurrell, 1995), while precipitation in subtropical northwestern Africa and the Iberian Peninsula is on a declining trend (Ward et al., 1999).

In the eastern Mediterranean, both the Atlantic Ocean and the Mediterranean Sea are the primary source regions for the formation of winter precipitation in the form of mid-latitude cyclones (Turkes, 1996). These migratory low-pressure systems have four primary cyclonic centers near Crete, Cyprus, southern Italy, and the Gulf of Genoa. Cullen and de-Menocal (2000) found a physical link between precipitation in the eastern

AGRICULTURAL DROUGHT IN THE NEAR EAST 213 Table 16.3 Intraseasonal droughts at Tel Hadya, Syriaa

Early season Mid-season Late season

1978-79

1979-80

1980-81

1981-82

1982-83

1983-84

1984-85

1985-86

1986-87

1987-88

1988-89

1989-90

1990-91

1991-92

1992-93

1993-94

1994-95

1995-96

1996-97

1997-98

1998-99

1999-00

2000-01

Note: 1: mild drought; 2: severe drought.

Mediterranean and the NAO and its impact on the stream flow of the Tigris and Euphrates. Their analysis indicates that during positive-NAO years, Turkey (and to a lesser extent northern Syria) become cooler and drier, whereas during negative-NAO years anomalous warmer and wetter conditions prevail. Both in the Maghreb countries, particularly Morocco, and in the eastern Mediterranean a link thus appears to exist with North Atlantic sources of climatic variability. The predictability of this phenomenon and its application in early warning systems will be explored further on.

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