Geology and Climate Relating to Archaeological Water Management in Jordan- Juniper Publishers
Archaeology & Anthropology- Juniper Publishers
Abstract
All questions concerning water management in Jordan
through time must begin with the ways in which water becomes naturally
available in the environment, and this depends crucially on the two
interlinked factors of geology and climate. Although these are natural
factors, they may also be affected by human activity, to produce changes
that are both planned and unplanned. It must be said that studies which
consider anthropogenic impacts on, for example, soils in Jordan are
just at the beginning. To date it is still hard to separate out
long-term, short-term and medium-term changes and to ascribe these with
certainty to either natural fluctuations or human activities. In many
cases the way the landscape has changed at a micro-regional level must
be to do with a complex interplay of natural and cultural factors. This
paper presents an overview of the geology of Jordan as currently
understood, a description of the modern climatic regime, a summary of
the limited amount of paleoclimatic data we have and concludes with a
discussion of the implications for research on the archaeology of water
management.
Introduction
Much of the principal evidence in this research
involves the identification and interpretation of obvious interventions
into hard geology, taking the form of excavated wells, cisterns and
channels. At a local level, it is also possible to see how walls, by
damming up or slowing down rainwater, have influenced slope wash and
thus the way soils have been eroded or sedimented up. Geology plays an
important role in whether wells can be dug and where; it is also crucial
for determining whether a well can be dug relatively shallowly or needs
to be extremely deep (the deepest prehistoric well in the overall
region being the probably Bronze Age example at Lachish in Palestine at
76m: Withe & Shqiarat [1,2]. In short, geology, therefore, is more
likely to account for differences in the number of wells in a locality
than any personal preference or technical skill when different
settlements and urban centres are compared [3-5].
Basic Geological Structure
The modern state of Jordan covers an area of
approximately 90,000 km2 and is located at the north-western edge of the
Nubo-Arabian plate. It has a predominantly limestone geology, with
surface flint pebbles, but this gives way to basalt in the north and
granite in the south. The south also includes the distinctive canyoned
sandstone zone in which the famous archaeological remains of the
Nabataean city of Petra are found. Topographically, the western border
with Palestine is
formed by the rift valley of the river Jordan, the Wadi Araba and the
Dead Sea. This rift is bounded to the east by the long line of the Jabal
As-Sarah Mountains. Beyond this is a broad plateau which eventually
gives way to the desert bordering Iraq in the northeast and slopes
gently down toward the synclinal depression of Saudi Arabia in the east
and south. Rivers in this region are seasonal wadi systems, which
contain water only in winter. The central limestone region is karstic
and displays a typical changeability in relation to the locations of
active springs and streams as the underlying geology is actively
remodelled. The climate is predominantly East Mediterranean in nature.
The north of the country receives adequate rainfall, while the south has
a more arid regime. Soils are varied and Jordan can be divided into
four main vegetation zones. It is impossible to understand water
management issues in Jordan in the past or present without a detailed
understanding of geology, soils and climate, and how aspects of these
may have changed over time, in response to long-term natural
environmental fluctuations, the constant volatility of the karst zone,
and medium and short term anthropogenic impacts [6].
Many geologists have worked on the geology of Jordan,
such as Blankenhorn, Quennell, Burden, Wetzel & Morton, Bender
& [7-10]. The Natural Resources Authority (NRA) is currently
carrying out a detailed map of Jordan on a scale of 1:50000 and tables
shows the stratigraphical sub divisions of Jordan, which covers the age
from Precambrian to recent times. The geological
structure of Jordan is well known as a result of work by Bender,
Quennel, Burden & Parker [7,9,11,12] and others. Although
more recent investigation and drilling has assisted in defining
and revealed significant new structural trends which were not
identified by the earlier studies, such mapping in not generally
available. It has thus not been possible to map the major casestudy
sites discussed in this thesis against a detailed geological
background. Figure 1 reproduces Bender’s general scheme with
the major case study sites superimposed.
Regionally, the structure of the study area is affected by
the presence of the Nubo-Arabian Shield and the formation of
the Wadi Araba-Jordan Rift. The southern part of Jordan is the
northern rim of the Nubo-Arabian Shield, which is built up of
crystalline rocks representing the base to the Precambrian age.
The crystalline rocks represent the base of the sedimentary
formation of the Arabian Peninsula [9]. The Wadi Araba-
Jordan Rift forms a 360km long section of the East Africa-North
Syrian Fault system. A system is recognisable over 6000km.
The structural pattern, as seen in exposures on the east side of
the rift, and the morphology of the surface of the Precambrian
Basement complex suggest that a structural zone of weakness
(geosuture) already existed at the end of the Precambrian
periods. The occurrences of late Proterozoic Cambrian quartz
porphyry volcanism in the southern Wadi Araba, the thickness
and facies changes in the sedimentary successions from Araba, and the thickness and facies changes in the sedimentary
successions from the Cambrian to the Lower Tertiary, indicate
the continued tectonic activity of the geosuture. However, the
Nubo-Arabian Shield in Southern Jordan plunges regionally to
the north and north-east. Epi-erogenic movements affected
the Palaeozoic strata in southern Jordan, resulting in the
gentle regional dip of these strata to the north and northeast.
The Palaesozoic formations were, in part, eroded before the
deposition of lower cretaceous clastic rocks. Therefore, from
west to east in south Jordan, the lower cretaceous rocks overlie,
with angular unconformity, progressively younger Palaeozoic
rock units that range in age from Cambrian in the west to upper
Silurian in the east.
The taphrogenic structural movements that initiated the
formation of the present rift apparently occurred along the preexisting
geosuture and started during the late Eocene-Oligocene
periods. In the late Oligocene-Miocene periods, the Jordan block
was subjected to uplifting movements resulting in continental
erosion and locally continental deposition of syntectonic
conglomerates in some places in the southern part of the rift.
Major Taphrogenic movements restarted in the Pliocene-
Pleistocene periods and continued during several intra-
Plesistocene phases associated with the wide-spread basalt
volcanism of the Middle Pleistocene age. The post Oligocene
taphrogenic structural movements were mostly of dip slip type.
Only minor local movements of tangential compression and
lateral displacement have been observed. Quennell and Freund
believed that major strike slip displacement had occurred along
the rift of the order of 70km to more than 100km, but this idea
was not supported by Bender & Madler [13].
Taphrogenic movement in the rift strongly affected the area
bordering the rift, chiefly along north-west, north-northeast
striking normal faults, antithetic and flexures of minor
displacements occur in the area. A few small anticlines in Central
and Southern Jordan, such as at Thunah, northwest of Ma’an can
be explained by tangential compression. The pattern of dominant
block faults in central and southern Jordan gradually changes
northwards into another structural pattern in north Jordan,
where up warping and tilting becomes a common feature with
faulting. However, the relatively thin and dominantly competent
beds in the south, reacted to structural stresses by fracturing
and faulting, whereas the thicker and more incompetent beds
in the north reacted to the same stresses by arching, tilting and
flexuring, for example, the northwest striking anticlinal trend of
Jabal Safra, southeast of Amman, the uplift of Suweileh northwest
of Amman, and the up warp of Ajlun.
Structural Features in Jordan
The main structural features in Jordan are the Jordan valley,
the Wadi Araba Rift Valley, and the folds and synsedimentary
structures in the Sirhan and Azraq basins. The faults in Jordan
are normal and extend northwest (e.g. the El-Hasa and El Karak
faults). The main structure is the Wadi Shueib structure which
extends north east folds and converts to flexure in the Baq’a
area [14]. The Amman Hallabat fold structure appears north
of Na’ur and extends eastwards passing, the southern part of
Amman [15]. The southern part of Jordan is considered part
of the Gulf of Aqaba-Dead Sea transform fault system, and as a
complex structural feature, which comprises the Gulf of Aqaba,
the Wadi Araba, the Dead Sea and the Jordan valley [16]. The Gulf
of Aqaba-Dead Sea structure, however, is described in terms of
plate tectonic theory as a transform type of fault where sinistral
movement took place between the Arabian Plate and the Sinai-
Palestine Plate [17]. A sinistral movement along the Gulf of
Aqaba-Dead Sea transform took place during several phases of
movement in the Neogene age [18].
The total thickness of all post-Proterozoic sedimentary rock
is generally 2000-3000m. The Nubo-Arabian shield, which is
of Precambrian date is exposed in south-western Jordan and
extends under most of Africa and the Arabian Peninsula. It is
characterised by Precambrian plutonic and metamorphic rocks
and some minor occurrences of Upper Proterozoic sedimentary
rocks, which is known as the Precambrian basement complex.
The Precambrian basement complex has repeatedly moved
up and down during epillarsogenic activities ranging in age
from Cambrian to early Tertiary. These movements resulted in
several marine transgressions and regressions of the Tethys
Sea, which lay to the west and northwest, over part, or all of
Jordan. The basement complex produced the material from
which, during certain periods, continental sediments were
deposited in the Tethys Sea. During the transgressions, marine
sediments of considerable thickness were laid down. Inland of
the transgression coastlines, and during intervals of regression,
terrestrial deposits accumulated: these consist mainly of
sandstone of the Nubian facies with no or few fossils. This
pattern of regressions and transgressions explains the pattern
of the different lithofacies-marine calcareous, marine sandy
and continental sandy- of Cambrian, Ordovician and Silurian
sandstone and shale of continental and marine origin, which,
unconformably overlie the rocks of the Precambrian basement
complex. The rock units, gently dipping towards the north and
northeast become overlain by a succession of younger marine
sediments, which are mostly made of carbonate of Upper
Cretaceous to Eocene in age.
Regionally, the marine influences on the deposition increase
toward the north and west during the transgressive intervals
of the Middle Cambrian, Early Ordovician, Early and Middle
Triassic, Middle Jurassic and Middle Cretaceous to Oligocene
times. Different shorelines have been formed due to these
successive transgressions. The sedimentary belt in Jordan,
results from the sepillarsogenetic movement that was repeated
several times from Cambrian to tertiary times and resulted in
a series of marine transgressions and regressions of shallow,
Sepicontinental Sea (Tethys Sea). The sedimentary rocks cover
wide areas of Jordan.
Soil and Vegetation Cover
Soils
Investigations of Jordanian soils, carried out by many
workers, have been summarised by Bender & Aresvik [19], but it
has unfortunately not been possible to locate a map showing the
spatial distribution of Jordanian soils from any published sources
known to the present author. gives a description of soil types as
summarised by them. Red Mediterranean soil covers extensive
areas along the high lands east of the rift from Ajlun, via Madaba,
Karak and Tafliah, as far as Shawbak. It has been noticed in the
eastern part of Tafliah sheet and is used for agriculture. The soil
is red to brown in colour as a result of the iron oxide content. The
thickness of the soil ranges from 0.7m to 1.5m and is Holocene
(recent) in age [2].
Soil and vegetation cover are indicators of the quantity of
precipitation, temperature and altitude. They change from
grey lowland desertic soil, with perennial shrubs developed
in areas with less than 150mm mean annual rainfall, to brown
soils with a complete cover of perennial shrubs and grasses in
areas having a mean annual rainfall of 150-300mm. Further to
the west and along the Western Highlands, as the altitude and
precipitation increases and temperatures decrease, red and
yellow Mediterranean soils with mountain forest are developed
in areas where the mean annual rainfall exceeds 300mm. Other
smaller biotic communities grow where hydrologic conditions
are favourable. The most prevalent is the dense growth of
phreaphytes commonly found along perennial and intermittent
stream courses. In some areas, azonal soils are developed, such
as the weathered basalt in the northeast, the saline soils in the
topographic depressions (in Azraq, Hasa and Jafer), alluvial soils
and regosols formed from recently deposited detrital materials,
and lithosols - thinly covered consolidated rocks such as basalt
flows.
Vegetation
The distribution of vegetation in Jordan follows the
variations in the amount of precipitation. Where there are
enough precipitation forests exist. Where there is little rain there
is steppe and where there is no rain there is desert. The rain is
not the only factor controlling the distribution of the vegetation
cover: soil, geology, underground water and differences in
temperature play an important role. In the higher parts of the
upland regions, where the rainfall is more than 300mm, the
vegetation is of distinctly Mediterranean type, with forests of
pines and other varieties, for instance oak and bushes. Due to
overgrazing, agriculture and firewood cutting, the forest areas
have shrunk to a narrow discontinuous strip along the eastern
escarpment of the Rift Valley and, occasionally, to patches on
top of the highlands. This forest has been destroyed over the
centuries, for fuel, agriculture and grazing [20].
In the steppe region the climate is more continental than
Mediterranean. Rainfall varies between 150mm and 300mm
and, generally, the plant cover is grass and Artemisia, especially
where soils are relatively stable. In the desert region rainfall is
generally below 100mm. The vegetation is extremely poor in
both variety and density, except in wadi bottoms, channels and
depressions. In the sandy desert, such extensive bare surfaces
are not common but, in between the individual shrubs, the
grounds are quite bare of vegetation: occasionally a few short
annual grasses are found. Between the steppe and desert regions
there is a broad transitional zone, linked to steadily decreasing
precipitation levels [19].
Climatic Overview
Most writers agree that the general climatic conditions
prevalent in all parts of the Levant today emerged during the
Early Bronze Age II and III 3000-2400BC [21]. The climate in
Jordan can be divided into two major types: the Mediterranean
type on the Western Highlands and the semi-arid to arid type
on most of the Central Plateau and Eastern Desert. The climate
is characterised by cold winters and hot dry summers. January
is the coldest month and August is the hottest. Average annual
temperatures range from about 13 °C in some high mountainous
areas to about 18.7 °C in the lowlands and the extreme southeastern
area. Temperatures are subject to large daily and
seasonal fluctuations. Monthly temperatures vary between 5
and 25 °C. Large variations in temperature also occur within
short distances due to topography.
Rainfall is primarily controlled by the Eastern Europe and
Western Mediterranean cold fronts, which are drawn by the
Eastern Mediterranean low-pressure system. Rainfall in the study
area is seasonal, occurring in the period October to May with
the highest fall in December and January. Rainfall outside this
period would be an extremely rare event. Precipitation generally
decreases from west to east and from north to south. However,
this pattern changes locally in some areas owing to orographic
effects over the high elevations of the Western Highlands. The
mean annual precipitation decreases from about 600mm/a in
the northern Western Highlands to less than 50mm/a in the
south-eastern desert. However, in the eastern and south-eastern
deserts, extended periods of no rain and periods of flooding are
not unusual (Figure 2).
Latitude is the main determining factor of climatic zones.
The latitude of a place, together with its elevation and relation
to surrounding relief, determines the light and heat received
from the sun. In the tropics, the intensity of insulation is greater
than at other latitudes because the sun’s rays fall vertically on
the surface of the earth, so that a bundle of rays of a given wide
is spread over the minimum possible area and has the shortest
possible passage through the atmosphere. The inclination angle
of radiation, absorption and the long of night and day also vary
in relation to latitude, whereas inclination angle of radiation
decreases with latitude. Therefore, light and heat decrease
pole wards. In summer, the duration of sunlight increases with increasing latitude and decreases in winter. Thus, in summer, the
low intensity of insolation in high latitudes is partly offset by the
greater long of day up to 43 30 °N, where maximum insolation
is reached.
Because of the low angle of the sun between the latitudes
of 43 30° and 62 °N, the amount of insolation decreases to a
minimum at the latitude (62 °N), the length of day increases
rapidly until, at the Arctic Circle, it is 24 hours long. Beyond
the Arctic Circle to 23° 30° at the pole. Also, annual ranges of
temperature, radiation and the long of night and day increase
with increasing latitude. At the Equator the day is 12 hours long
throughout the year. Day long increases with increasing latitude
until, at the poles, there is six months of day followed by six
months of night. At the equator, the amount of insolation received
varies little throughout the year, for the range of the long of day
is close to zero. At midsummer, north and south of the equator,
insolation is greater both at the Tropics of Cancer and Capricorn
than it ever is at the equator, for the duration is longer and the
intensity is just as great, the sun being directly overhead [22].
Furthermore, in the Tropics there are fewer clouds than over the
equator on most days of the year. Therefore, zones at about 20°
north and south in summer receive the greatest insolation on
the earth [23] As a result; the extremely hot and dry deserts of
the world are within the tropical and sub-tropical zone. Cyclones
of mostly Mediterranean origin usually start affecting Jordan in
mid- October or early November and dominate the weather until
late April [24].
Jordan lies within the Mediterranean bioclimatic region
of semi-arid to arid type [25,26]. The essential features of this
climate are dry, hot summers and cool winters. The climate
regime is determined by the interaction of two major atmospheric
circulation patterns. During the winter, the temperate latitude
climatic belt prevails, and moist cool air moves eastward from
the Mediterranean. In the summer, the subtropical high-pressure
belt of dry air causes relatively high temperatures and no
rainfall. Weather parameters such as atmospheric temperature
variations, air pressure and relative humidity. Jordan is part
of the eastern Mediterranean weather system and has a
climate with distinct seasons in different areas of the country,
including wet and cool-to-cold, with occasional snowstorms.
In the highlands there are often temperatures several degrees
centigrade high than in the range of hills overlooking the valley
to the north. There are marked seasonal contrasts, however:
summers are dry and warm-to-hot and winters are wet and coolto-
cold, with occasional snowstorms. In the highlands, there are
often strong, cool breezes on summer nights and low-lying areas
enjoy pleasant, moderately cool winters.
January is the coldest month and, although belowfreezing
temperatures are not unknown, the average winter
temperature is above 7.2 °C. The hottest month is August, when
temperatures may reach 48.9 °C in the Jordan valley. In Amman,
the average summer temperature is a pleasant 25.6 °C. Rainfall
is mostly during the winter months and ranges from 660mm
in the northwest to less than 127mm in the east of the region
[24,27,28]. The climatic features of the area can be described by
considering north-south and west-east trends. The climate in
the northern and western mountainous areas is Mediterranean
but, moving eastward, there is a rapid change to semi-arid and
arid types, as the influence of the Mediterranean Sea is replaced
by that of the continental land mass, causing a decrease in
rainfall and an increase in the temperature range. Farther to the
southeast, in the El Jafr Basin, the climate has been classified
as arid or as a Mediterranean Saharian climate of the warm
variety [25]. Additionally, there is a marked secondary influence
of topography upon the climatic parameters throughout the
country.
The relative humidity in the Ghor varies from 70% in winter
to less than 50% in summer while, in the eastern plateau, the
variation is from 75% to 35%. Dew originates from the cooler
winds of the Mediterranean and occurs in summer, gives
beneficial moisture supplying to summer crops grown under dry
farming conditions [19]. In the Wadi Araba, there is no indication
that the climate has ever been other than semi-arid within recent
times, but it is reasonable to suppose some variation within the
semi-arid range, and that at different times the streams have
flowed more strongly, and further than at present. In the Wadi
Araba, the present rainfall is estimated at between 50mm in
a dry year and 150mm in wet year, a falling mainly between
November and April [29].
Climatic Zones
Jordan can be divided into three physiographic regions, each
with a distinct climate
a. The highlands comprise mountainous and hilly regions
that run through Jordan from north to south. Several valleys
and riverbeds intersect the highlands, such as Wadi Mujib,
Wadi Hassa and Wadi Zarqa, all of which eventually flow
into the Jordan River, the Rift valley or the Dead Sea. The
highlands are by no means uniform. Their altitude varies
from 600 to 1600 metres (1969-5249 feet) above sea level
and the climate, although generally wet and cool, also varies
from one area to another. It is in the highlands that we find
the major remains of ancient civilisation in the cities of Petra,
Jerash, Philadelphia (Amman), Madaba, Gadara (Umm Qais)
and Karak. For much the same reasons, abundance of water
and strategic location, the highlands are the most densely
populated areas today.
b. West of the highlands is the Jordan Rift Valley, which
runs along the entire length of Jordan. The Rift Valley plunges
to over 400m (1312 feet) below sea level at the Dead Sea,
becoming the lowest spot on earth, and reaches a minimum
wide of 15 kilometres. The Rift Valley encompasses the
Jordan (the Ghor in Arabic), the Dead Sea, Wadi Araba and
Aqaba. The Rift Valley is rich in water resources, including
thermal mineral water. Therapeutic treatment is available at
Zarqa Mai’n, a deep gorge close to the Dead Sea with over 60
mineral springs. The Valley is rich in agricultural land and is
warm throughout the year.
c. The desert region in east Jordan is an extension of the
Arabian Desert; it is a semi-arid, steppe-like region in which
small plants survive in winter and spring.
There is extreme variation in the climate of the desert
between day and night, and between summer and winter.
Summer temperatures can exceed 40 degrees Celsius, while
winter nights can be bitterly cold, dry and windy [28].
Effects of Water Bodies
Next to the variation of insulation with latitude, the
distribution of land water on the earth is the most important
factor affecting climate. Water conserves more heat than land:
being slower to warm up and slower to cool down it has a
moderating influence on temperature [22]. So, temperature
ranges in Jordan increase with increasing distance inland, in
parallel with increasing continentality. The nearest large body
of water which affects the climate of Jordan is the Mediterranean
Sea. Both land masses and water bodies affect the climate of
the Jordan, but the landmasses have a much bigger influence
than the water bodies. Consequently, the climate of Jordan is
characteristically an arid, continental climate: it is dry and hot,
with a large temperature range between day and night, and between summer and winter, especially in the Jordan Valley, the
Aqaba Region, and wet and cool-to-cold in the highlands [30,31].
The most stable season in Jordan is summer. The following
major changes occur in the pressure fields over the eastern
Mediterranean due to the intensive heating of landmasses. First,
a centre of high-pressure forms over the Mediterranean. Then a
low-pressure region develops during the summer months and
extends from North Africa to Pakistan and India through the
Arabian Peninsula and Indian Oceans. This huge low-pressure
belt brings the eastern Mediterranean within the monsoon belt
of southern Asia and invites hot and dry northerly continental
tropical air masses from the high-pressure centres over
Mesopotamia, Asia Minor and the lowland around the Caspian
Sea. Two centres of low-pressure cut-off are formed over the
northern Red Sea and Saudi Arabia. The hot winds blow from the
Rub-al-Khali (the Empty Quarter, bringing occasional invasions
of very hot air masses, which raise the temperature to very high
levels and cause heat waves [24].
In winter, meridional circulation of the upper air over the
eastern Mediterranean is related to the differential heating
between the warm waters of the Mediterranean and the cold
landmasses of southern Europe and the Atlas Mountains. Deep
upper air troughs are correlated with the invasion of the region
by cold polar air masses. When a sonal circulation prevails, waves
form over the Mediterranean and move rapidly toward the east
causing light rainfall and near average temperatures. The main
features of the pressure distribution during the winter are that,
over the Arabian Peninsula, Armenia, Turkey and northern Iraq,
high-pressure centres develop. The thermal difference between
the Mediterranean waters and the land masses lying to the north
and south then causes low pressure centres to develop over
the central and eastern Mediterranean, and the Azores highpressure
centre extends to the areas lying south of the Atlas
Mountains [24].
The eastern Mediterranean is invaded by different types
of air masses including cold arctic air masses and cold polar
air masses, which are usually associated with anticyclones or
ridges of high pressure. Especially in autumn and spring there
are continental tropical air masses, which come from North
Africa. In winter, the Mediterranean is occupied by one of the
normal frontal zones in which disturbances frequently develop
and move eastward. Frontogenesis relates to the sharp contrast
in temperature and humidity between continental tropical air
masses and the cold polar air masses. Short fluctuations of low
temperature which occur in Jordan during the winter are usually
associated with cold fronts, but severe outbreaks of cold weather
are caused by cold pools and cold lows.
The weather in Jordan and other eastern Mediterranean
countries is dominated in winter by a series of depressions, which
move along the Mediterranean front from west or southwest
to east and northeast. Most Mediterranean depressions form
as lee or wave depressions over the Mediterranean [24]. The
general conditions favouring cyclogenesis are the existence of a
baroclinic or frontal zone, air convergence on the leeward slopes
of the Alps and instability of air masses. The Mediterranean
depressions may be grouped according to their areas of formation
and include depressions of the western Mediterranean basin,
which are usually called ‘Genoa depressions’ and which do not
usually reach the eastern Mediterranean and therefore have no
effect upon the climate of Jordan. Khamasin depressions are
frequently called Saharan depressions because they form in the
area south of the Atlas Mountains and move along the southern
shores of the Mediterranean. Most of these depressions, which
account for 18 per cent of the Mediterranean depressions,
occur during the spring. Depressions of the central and eastern
Mediterranean sometimes form in the northern Ionian Sea, the
southern Aegean Sea and the region of Cyprus, but the formation
of new depressions in this area is rare and what is more common
is the rejuvenation of old weak depressions, especially in the
neighbourhood of Cyprus.
Most depressions in the eastern Mediterranean move along
three main tracks with an annual average of 10.5 depressions
moving to the northeast through northern Syria and southern
Turkey. Eleven depressions move annually to the east and a few
of them reach northern Iraq, with an average of 1.5 depressions
moving to the southeast. The decreasing number of cyclones
moving in southern tracks explains the decrease of annual
rainfall in Jordan from north to south [24]. In winter, the climate
of Jordan is influenced more by conditions in the Mediterranean.
The main sources of rainfall for the country are the Mediterranean
Sea in winter and the monsoon in summer. The influence of the
Mediterranean Sea on the climate of Jordan decreases towards
the south and north. Cyclones from the Mediterranean may bring
winter rains as far south as 20 N°.
Effects of Mountain Bodies
Mountain ranges are important climatic factors because
they interfere with the flow of air. A mountain range restricts
the influence of the seas, acting as a barrier to the inland
passage of moist air. There are differences in the annual
and diurnal variations of temperatures between maritimeinfluenced
regions, and regions on the lee of mountain barriers
which are sheltered from maritime influences. Furthermore,
it is known that temperature decreases, and rainfall increases
with increasing altitude. Therefore, the As-Sarah Mountains
(Shawbak, Ajlun and Negeb), which run parallel to the Red Sea,
are affected by maritime influences, which bring rain, much more
than the low areas located to the east and west of the mountain
ranges, or even the coastal plain which runs parallel between
the Dead Sea and As-Sarah mountains. At the same time, these
mountain ranges restrict marine influences on a short distance
from the coastline [32]. As a result, rainfall in the mountains
falls mainly on the As-Sarah Mountains, and little falls over the
northern plateau and the coastal plain, Also, the daily and yearly
temperature ranges, which give an indication of the degree of continentally of the climate in the northern plateau areas, are
larger than those in the mountain ranges and coastal plain.
There are no other important mountain ranges in the country
that affect the climate. However, because the country is small,
some local variations occur, especially between the southern and
northern regions
The Biogeographical Regions in Jordan
Long [25] divided Jordan into nine bioclimatic regions, based
on the analysis of climatic data from twenty-four stations in
Eastern Jordan. Al-Eisawi [33] followed the same method as long.
The climatic, rainfall and temperature of data thirty-one stations
between 1966 and 1980 was analysed and the distribution of
the resulting bioclimatic zones. Among the studied stations are
Shawbak (close to Petra). This is considered to lie in a semi-arid
Mediterranean bioclimatic zone of cool variety.
Conclusion
The distribution of the archaeological sites in Jordan has
been affected by climate change throughout the history of the
area. The data obtained from the Jordan Antiquity Information
System (JADIS) demonstrates that the number of archaeological
sites in Jordan increased during wet periods but declined during
dry ones. Previous site occupation, soil fertility and proximity
to water are the physical characteristics of the reoccupied sites,
even during unfavourable climatic episodes. The prehistoric
people who inhabited Jordan responded to climate changes
through migration to these favourable sites.
In his chapter ‘Climatic Changes in Jordan through Time’ in
the Archaeology of Jordan volume (which he co-edited) Burton
MacDonald writes that: “A wetter phase is one of the explanations
for the occurrences of widespread silts from Qadesh Barnea in
the south to the central Shephela region in the north, during the
Byzantine and Early Islamic periods, that is, between roughly
1600 and 600 Bp [34,35]. The widespread silts, however,
could have been caused by the influence of human activity on
the landscape in the form, for example, of deforestation and
over-grazing. Archaeology supports the hypothesis of a wetter
climate since the area was densely occupied by large Byzantine
settlements. It is hard to envisage how such a large population
could survive under the regime of today’s arid conditions.
There is a circular element to this argument, and it could be
argued that MacDonald’s assumption is possible based on under
appreciation of the sophistication of Nabataean and Roman-
Byzantine water management systems. What is clear from this,
however, is that lack of good quality data on climate change
means that understanding changing water management patterns
fully remains difficult. MacDonald & Goldberg [34] recognizes
that independent verification of his hypothesis is needed using
techniques such as palynology. In general, it must be accepted
that the prehistoric people who inhabited Jordan responded to
climate changes through migration to more favourable areas
both within and outside what now constitute the borders of
modern-day Jordan. The Dead Sea levels, presented by Frumkin
[36] as indicators of paleoclimate in the area, match the number
and distribution of archaeological sites in Jordan during the same
periods. One could argue that site reoccupation in prehistory has
a positive relationship to moist climate conditions and could be
used as paleoclimatic indicators in the absence of chemical and
isotopic analyses. The variations in the local climate of Jordan
motivated early settlers to reside in, and occupy, the areas of
north and middle Jordan. Access to water resources was a major
factor in site distribution in Jordan and encouraged reoccupation
even in dry periods.
The study by Frumkin & Carmi [37] did not focus on seasonal
climate variations and human adaptation to such variations;
further studies in the area are needed in order to have a complete
picture of the seasonal climate throughout the prehistory of
Jordan. In the North African climate, following a wet phase from
40,000 and 20,000 BC, with the last major pluvial at 6,000 BC
and significant climatic change between 4,000-2,000 BC there
has not been substantial climatic change since 2,000 BC. In
general, we might expect that Jordan follows the North African
pattern, with no major climate changes during the period
under study here (later prehistoric through to present). It has
been postulated that the region experienced a slightly moister
environment at one or two points during the classical period
[36,38]. However, these scholars are rather unspecific about
the data they use to support this suggestion and are not exact in
defining precise chronological units. Much more work needs to
be undertaken before a clearer assessment can be made and the
implications for core and peripheral regions of Jordan deduced.
Gaining higher-quality paleoclimatic data is an important
future research objective because, even if there were no major
shifts in the last four millennia, even minor shifts can have major
effects on what is possible or impossible in subsistence terms.
In short, if water management technology is sophisticated,
then a lot of extra benefit can be derived from even minor
increases in precipitation. One could argue that the pattern of
the spatial and temporal distribution of archaeological sites
in Jordan might have been determined by climate, but without
adequate supporting data this can only be a supposition. One
of the most impressive revelations concerning ancient water
supply and management has been the important role which
geological terrain, particularly karst, played in the ability to
access and utilise available water. The volatility or dynamism
of the limestone karst landscape has been described above, and
the water-created subsurface tunnelling, caverns, sinkholes, and
springs, have always been relatively easy to discern. To date,
however, relatively little archaeological work has been done in
these contexts. In general, similar water-management structures
- wells, cisterns, aqueducts, etc - are found on the sandstone as on
the limestone regions of Jordan, while absent from the basaltic
formations of the north - the earthquake zone.
Karst is the prevailing geology throughout much of the
Mediterranean region and played an important role in the
water supply of numerous cities in Antiquity. Dora Crouch
presents clear evidence that most, if not all, Greek cites were
established either on or near karst terrain [39], while Dan Gill’s
recent article about Hezekiah’s Tunnel in Jerusalem clearly
demonstrates that naturally-created the tunnels and shafts were
enlarged deliberately in order to channel more valley water to
city [40]. Thus, it seems that people utilised karst terrain to
their advantage throughout the Mediterranean. While nature
provided the basics for a well-watered site, it was still up to the
humans who inhabited the area to develop and utilise the water
in the ways they desired [41-43].
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