Introduction

This article summarizes the results of the investigations by the author and his collaborators, since 1981. These were published in a series of papers and books the most recent is the book by Arie S. Issar and Mattanyah Zohar  "Climate Change - Environment and History of the Near East", which was published in 2007  by Springer –(Berlin, Heidelberg, New York). It is the second editon of the book "Climate Change – Environment and Civilization in the Middle East", by these two authors, published in 2004. Also in 2007 Cambridge University Press reprinted the book "Climate Changes during the Holocene and their Impact on Hydrological Systems" by Issar, first published in 2003. In these books the principle of "The past is a key to the future" was applied. This involved a survey of the climate changes during the last ten thousand years, and their impact on the hydrological cycle, as well as the phyto-, bio- and human environments. In the Cambridge book it was done on a global scale, while in the books by published by Springer the investigation focused on the Middle East.  In the present paper the focus will be on Israel. The investigation of past climates was based on the interpretation of proxy data, which included paleo-sea and lake levels, pollen profiles in lake swamp  and sea sediments, environmental isotopes ratios in lake, sea and cave deposits as well as archaeological data.

Climate Regimes, present and past

The climate of the Middle East in general and Israel in particular are decided  by the Arbian – Saharan global desert belt, on one hand and on the other by the Mediterranean climate belt. The desert belt is decided by the existence and movements of the Inter tropical Convergence Zone (ITCZ), while the Mediterranean system is the most southern extension of the climate belt dominated by the westerlies. Along this belt, during winter, cold air masses brought by cyclonic low barometric pressures, arrive from the Atlantic Ocean and the North Sea.  While traveling over the warm water of the Mediterranean Sea these masses absorb humidity. When forced to ascend after crossing the coast line they cool and precipitate their excessive humidiy.  Rain events are dependent on the rate of southward movement of the cyclonic lows, which depends on the southward migration of the desert belt. When this belt remains over Israel, rainstorms will not travel south, which will diminish the number of the rain storms and will spell a dry year or years. The direction of the shoreline of the Coastal Plain bending west south to Gaza, decides the southern border of the path of  the cyclonic lows and thus decreases the number of rain storms travelling south. This border line causes the aridity of the southern half of Israel as can be seen from the multi-annual precipitation map (Figure 1).
              

Figure 1. Average precipitation map Israel (mm/y).

The mountains'  topography also has an influence on the precipitation thus the eastern foothills and the Rift Valley are in the shadow of the rain and therefore are relatively arid, while the western foothills to the crest line of the mountains receive, relatively more rain and snow.
Precipitation falls during the winter months, from November to March, the period during which the temperatures are relatively low and evaporation is also rather low. Thus, the relative effect of the winter rains is rather high. During summers and dry years the weather is rather stable, being affected by the semi-permanent surface heat trough centered over Iran and Iraq. This surface trough is coupled with the upper air high-pressure system of the Sahara-Arab desert belt .
The question which has to be answered first is whether this general climatic regime existed also in the proto-historical and historical past. The answer to this question can be answered by the study of the proxy environmental data, already mentioned.
In the first place all data show that in general the Negev was arid to semi arid during the Holocene, namely the last 10,000 years, which points to the fact that the westerlies regime was the main agent of bringing precipitation. As will be discussed later during cold global periods the Negev became more humid, but not as the northern and central parts of Israel.
Additional evidence can be derived from the isotopic composition of the stalagmites of the Soreq Cave west of Jerusalem on the slope of the Judaean anticlinorium at about 400 m above MSL and about 40 km inland from the Mediterranean Sea. Present average precipitation is about 500 mm/y. The cave contains stalagmites, which are still being formed due to water dripping from its roof.  A joint team of geologists and hydro-chemists headed by M. Bar-Mathews, from the Geological Survey of Israel, analyzed and compared the chemical and isotopic composition of the rings of the stalagmites to the composition of the cave water and the carbonates the dripping water (Figure 2). At the same time the isotopic composition of the rainwater above the cave was anlayzed and correlated with the meteorological data.

       

Figure 2. Correlation between data from Soreq Cave stalagmites and ancient levels of fhe Dead Sea

With regard to the climatic conditions during the Holocene it was found that at least after 7K B.P. (seven thousand years before the present) the proportions between the intensity of the rain, the temperatures and the oxygen 18 and deuterium composition of the cave's dripping water were similar to that of the present precipitation and the average composition of the stalagmites. Moreover the average oxygen and hydrogen isotopic ratios fall on the Mediterranean meteoric-line.

As the samples were dated by the ²³⁰thorium- uranium method the dating of the stalagmites was with an uncertainty range of not more than a few decades. The residence time of the water in the subsurface was found to be not more than a few decades. Thus it can be concluded that there was no significant change in the climatological regime  within the last 7000 years.
Support to this conclusion was obtained from the ancient levels of the Dead Sea. A pioneering survey was carried out by the geographer Dr. Cipora Klein in 1982 which showed that around 2000 years ago the fluctuating level of the Dead Sea reached a peak of about 70m higher than today. In the same period, the level of the Nile fell (Nicholson and Flohn, 1980) probably due to the weakening monsoon system. Amos Frumkin in a series of studies provided additional support for significant climate changes during historical periods (Fig. 2). He and his colleagues investigated the salt caves of Mount   
Sedom and discovered driftwood, which could be dated by ¹⁴C, deposited on the ancient high shorelines, created when the levels of the lake came up. On the other hand when the levels declined deep drainage channels below the present level of the bottom of the southern part, were developed.. The highest water level between 5K to 4.5K BP (which was the Early Bronze Period) reached about 300 meters below MSL (about 100 m above that of the present).  It was followed by a decline to below the altitude of the shallow bottom of the southern part of the Dead Sea, which dried up. The sea level was high again around 3K BP., i.e. the Iron Age and between 2.5K to about 1.4K BP, i.e. Roman and Byzantine period (with a short decline between 1.7K to1.6K BP). In the Moslem period, starting about 1.6K BP it again fell to an extreme low level. These observations were later generally confirmed,  with even a higher precision by R. Bookman (Ken-Tor) and her colleagues
Correlating the results of the investigations of the ancient Mediterranean Sea levels (Raban 1991, Raban and Galili 1986, Galili et al.1988) with that of the Dead Sea, shows that during cold periods the Mediterranean Sea levels fell, as a result of water accumulating in the glaciers, but at the same time, the level of the Dead Sea came up because of a colder and a more humid climate. In warm periods the reverse occurred i.e. Mediterranean Sea levls came up while Dead Sea levels declined.  An illustration to this can be seen in the harbour of Cesaerea where the paved street built by Herod, in a period which was cold, and the sea was low, is today covered by sea water.

Impact of paleo-climates on history a short review

Correlating the data from the Soreq Cave, ancient Mediterranean Sea and Dead Sea levels with archaeological data shows that during the cold and humid periods the many settlements spread into the desert areas, while during the warm dry periods the Negev and Southern Judea were deserted. In the following chapter this correlation will be elaborated.
The transition from the hunting-gathering way of life to farming took place in the Middle East some 10,000 years. The transition was gradual and started after the Last Glacial Period, which ended about 17K BP. During most of the Last Glacial period the Middle East enjoyed a humid climate the level of Lake Lisan the precursor of the Dead Sea came up to about 160 m below present MSL (Begin et al. 1985, Bartov et al 2002, Bookman et al 2006). The post glacial period climate became more arid and the Dead Sea shrank to its present geographical configuration.    
The first settlement which is known to live on agriculture is Jericho. Most likely that the diversion of the water of the spring of Elisha was the first irrigation project.
The second step of humanity forward after agriculture was the invention of pottery. This enabled storing, as well as cooking agricultural products. These steps were taken during the Neolithic period, which started about 10K BP, and included a Pre-Pottery phase succeeded by the Pottery Neolithic period. This period was characterized by climatic fluctuations. The general trend seems to have been humid during most of the period and dry towards its end, which was at about 6.5K years ago, demarcated by a gap in settlements in the semi arid part of the Middle East, which was caused by a warm and dry climate phase.
The new period was characterized by a new innovation, namely copper. As the people continued with the use of flint tools, this period is called the Chalcolithic Period (Chalco=copper, lithic=stone). Most probably the people who brought copper to the Middle East originated in the Caucasian Mountains of East Anatolia or the mountainous areas of Armenia. These people had to immigrate as the strong climatic change from warm and dry to cold and humid made the high plateaus of Anatolia, Iran and may be even Central Asia, less habitable. At the same time the plains of the Middle East flourished, as evidenced by a rise in the total number of farming communities in this region.
The Chalcolithic culture, with its artistic tradition and technical knowledge lasted for more than thousand years and suddenly disappeared about 5.3K BP. All the sites were abandoned without any signs of violence. As can be seen from the stalagmites of the Soreq cave (Figure 2), this was due to a severe climate change. These data also show that some time after 5K BP a major change brought a cooler and more humid climate to the Middle East and the introduction of a new metal i.e. Bronze.
During the first stage of the Bronze Period, i.e. the Early Bronze the climate was cold, and it is suggested that again the people of the central plateau of Asia moved towards the more hospitable south. As this period was very humid and the level of the Dead Sea rose by about 70m it is suggested that it was a period of intensive rains all over the Middle East and floods affected the low lying area like that of southern Mesopotamia. These floods were remembered by the ancient inhabitants of Sumer who wrote the epic of Gilgamesh, in which the story of the deluge is told and later retold as in the form of the Biblical Deluge. Various other arguments are brought by Issar (1990) and Issar and Zohar (2004, 2007) to prove that the Biblical Deluge was in Mesopotamia and during the cold and humid climate of the Early Bronze. On the other hand the marine geologists William Ryan and Walter Pitman in their book 'Noah's Flood: The New Scientific Discoveries about the Event that Changed History' argue that around 7500 years ago the melting of the worlds' glaciers caused the waters of the oceans to rise to an unprecedented level. At a certain point, the constantly rising waters eventually breached the barrier at the Bosphorus, at the northeastern part of the Sea of Marmara. Until then this barrier had separated the Mediterranean Sea from an ancient lake, the predecessor of the Black Sea, the level of which was 150 m lower than its present sea level. A tremendous waterfall of seawater began to cascade down flooding the lowlands surrounding the ancient lake, causing a calamity to the people in the Neolithic agricultural communities, which lived in this region.They further claimed that this calamity lived on in the memory of the people who survived and migrated into Mesopotamia. The stories told were passed on from one generation to the other until they crystallized in the mythological texts found on ancient clay tablets of ancient Mesopotamia. At a later period, these stories were incorporated into the Hebrews' sacred scriptures and became part of the Judeo-Christian-Moslem heritage. The present author does not argue against the paleo environmental story, deciphered by Ryan and Pitman, but maintains that it has nothing to do with the Biblical Deluge, except the commercial interest of selling the book.     
At the end of this period, at ca.4.2K BP urban centers, which had existed for several hundred years had all disappeared, being abandoned without any sign of destruction, the reasons for this regional devastation can be seen on Figure 2, namely again a warm and dry period. The level of the Dead Sea fell to a stage in which the southern part dried up. This climate change also led to a transition into a new culture, namely that of the Middle Bronze. During this period the climate ameliorated  This brought a major socio-economic change. Most of the abandoned urban Early Bronze sites were recovered and resettled, moreover, many new sites were established.
After a short period of a mild climate, another short but marked warm phase around 3.3 K BP triggered movement of people, among them the so-called Sea Peoples, some originating in the Aegean peninsula and others from different Mediterranean lands and islands. They appear to have moved by land and by sea into the Middle East. Shortly afterwards a cold global spell started and more or less in parallel the introduction of a new metal i.e. Iron, for which this period is named. Again the level of the Dead Sea rose by about 50m.  The desert of the Middle East flourished allowing the build-up of an extended trade network. This was the time the  Israelites settled down, first along the margins and later penetrated the more humid part of the country. At the same time the Aramaeans and the Nabateans built their cities and developed terracing and magnificent irrigation systems. In sequence Egypt, Assyria, Babylon, Persia, Greece and Rome extended their empires over this region.    
At ca. 600 AD the climate turned warm again. The sea level began to rise and gradually covered Roman port installations and other buildings all along the former shorelines, all the way from Caesarea in Palestine to Cadiz in Spain. On the other hand, the level of the Dead Sea fell below that of the present and its southern shallow part dried up. Due to the stronger monsoon regime the level of the Nile rose and the silts and sands it brought from the Nubian Desert and blown in from the coast of northern Africa, covered most of the coastal plain of Palestine. The once flourishing cities along the border of the desert were deserted, becoming stony ghost towns. Northern and central Arabia became drier due to its dependence on a weakened system of westerlies. This, and the desertion of the limes settlements of the Byzantine Empire plus the collapse of Persia, facilitated the momentum of the invasion of the Arab tribes under the banner of Islam, enabling them to conquer not only the entire Fertile Crescent but also northern Africa to the Iberian Peninsula and Iran.
At ca. 800 AD the warm climate reached its climax, which created optimal conditions in Europe causing an abrupt increase in population and a deficiency in cultivatable land. Some time after  1000 AD a cooler phase began and living conditions in Europe deteriorated, which may have triggered the movement of poor desperate people and knights with no estate to try and and gain new lands in the Middle East, which flourished due to a more humid climate. Thus the Crusades, which started more or less half a century later on the initiative of the Catholic Church, may have been influnced by the colder and therefore worsening conditions in Europe while the Near East became more hospitable.
During the coming two centuries Turkish Moslems’ states and Christian kingdoms rose and fell. A cold peak occurred during the Little Ice Age during which the Mameluk State flourished. It was later replaced by the Ottomans who became the rulers of the region for about four centuries.

Forecast for the future

The conclusions that can be drawn from this brief paleo-climatic and historical review is that the global warming will result in a drier climate to Israel. Assuming that the change will be in the order of magnitude, whch occurred after the Roman-Byazntine period when, according the isotopic curve in the Soreq cave, the decrease in the amount of rain from that period to the Arab period was on the order of 20-25%. This may come in series of drought years in which the amount of rain will be even less and is liable to reach 50% of the average. Thus the long term multi annual average may come down to about 30% of the present. At the same time, because of the intensification of the Indian Ocean monsoonal climate system following the warming of the oceans, strong rainstorms and floods may occur in the Negev.
It should be taken into consideration that although the general trend of aridification of the Middle East is due to global warming, there still exists a likelihood that a series of volcanic explosions may bring a decrease in the radiation and a temporary drop in the temperature of the oceans, and a number of rainy years, as in 1991, when Mount Pinatubo erupted. This brought an increase in the amount of precipitation in the Middle  East. On the other hand future aridization may be even worse than that of the past because the present warming process may be a natural warming process intensified by a green-house effect .
Groundwater recharge may decrease even more, as in warm years of low precipitation the evapotranspiration may be higher than the average. Thus it is suggested that the average groundwater recharge may be reduced by 30%.
The amount of recharge of the groundwater basins in the last 30 years has averaged about 1830 MCM (million m³/yr) (Hydrological Service Report 2000). Thus the climate change may bring this amount to the order of magnitude of 1200 which is about half of the demand forecasted for 2020, which according to the estimate of TAHAL (Water Planning for Israel 1990) is expected to reach about 2500 MCM
As previously mentioned, the main purpose of the present article is to warn against the negative impact of global warming on the the hydrological cycle of Israel, a danger, which the official institutes of Israel in charge on managing this resource, do not take seriously into consideration.  Still this negative impact, if recognizd in time, can be avoided if enough desalination and sewage treatment plants are built.
From the economic point of view, even now, the average level of income per capita in Israel enables paying for desalinized seawater for home consumption, whereas about half of the consumption for agriculture is likely to come from recycled treated sewage water. But even if the Israeli economy will have the sense to prepare the tools to contend with the average decrease in precipitation because of global warming, the question still remains as to how to overcome the distress following continuous series of drought years that are likely to come every few years, in which the amount of precipitation is liable to decrease to 50% of the average. It is hard to assume that it will be feasible to build another system of desalination for these cases whose frequencies and time of occurrence cannot be foreseen. A sharp reduction in agriculture is also an undesirable solution because this is liable to lead to the destruction of the foundation of this branch, which has social and environmental importance, despite its marginal importance from the national economic point of view.
There is thus a need for a long-term storage system to store the surplus surface water, which today flows to the sea. In years of above average precipitation treated sewage water could be stored in the winter months when agricultural demand is low, as could surplus fresh water from desalination plants in hours and seasons of low demand. The ideal storage site, due to its hydrogelogical charateristics is the Coastal Plain aquifer. This will mean reducing the quality of its water into a second class grade. In times and sites of need this can be remediated by partial desalination plants. In the south, especially when it comes to supply of water to Beer Sheva and surroundings partial desalination of the water from the fossil aquifers found under the Negev, was found to be more economic than transporting desalinized seawater (Pratt Report 2004). 
The conclusion stemming from the above-said is that there is an urgent need to prepare a new master plan that will take into consideration the forecast of the negative climatic change that is gradually being realized. Although, needless to note, the present article doesn’t presume to present such a plan.

Conclusions from the point of view of future energy resources   

As stated, the aridification anticipated for our region because of the Global Change phenomenon which is liable to decrease the perennial precipitation average by 20-30% and in years of stress even by 50% of the average demands the massive building of desalination plants of seawater a well as brackish water. The second source will mainly be the coastal aquifer, which should be recharged and operated as a national storage tank of second grade water. Likewise, a southern water project should be built that will enable extraction of water from the fossil aquifers of the Negev, their partial desalinization, and their transport to the Beer Sheva area.
Needless to say that this massive increase in the desalinization of water will demand an augmentation of the supply of power. Up to now Israel's power supply is based on fossil fuels. Although Israel is not included in the list of the countries required by the Kyoto protocol to control its atmospheric carbon emmissions, such a control will be required as the global situation of enrichment of atmospheric carbon increases parallel to the increase of the temperatureof global atmosphere.
Here is a challenge to the community of physicists, meteorologists  and engineers to combine efforts in order to increase the part of green energy resources to replace the existing  power stations as well as that turning the wheels of transportation facilities. It is beyond the speciality of the present author to describe the potential green energy projects. In the framework of the discussion of the water resources a few of future green energy projects will be mentioned.
Hydro-electric power to be generated by a project, which will base on a canal-tunnel from the Mediterranean Sea to the Dead Sea, through the Valleys of Izrael and Jordan River. Investigations carried out by the author and his team have shown that this track involves no danger to groundwater, is of minimum requirement of tunneling and enables maximum marginal benefits, like inland desalination plants, aqua-culture projects and the option to precipitate carbonates and sulphates from seawater, once these components prove to cause whitening of the Dead Sea Water.
Rejuvination of the investigations of producing power from "Solar Hot-Pools" i.e. pools in which brines as solar heat collectors underlie brackish water upper layer insolators. Once the technological problems, encountered in the failed pilot project, will be solved, the Med-Dead Sea project may supply an additional source of energy.
The planting of trees to be irrigated by flood as well as fossil water found under the Negev. In the first place plants which may supply bio-fuels such as jojoba and jatropha. In the second place for the production of dates, olives etc. as well as wood for local power stations.  It is suggested when all benefits, direct and marginal, are considered on a long-term scale, such plantations has a good chance of being economically viable. In the list of benefits one should take into account also the sequestering of atmospheric carbon, which may become an important economical issue in the future.

General Conclusions

The interpretation of the various proxy data of the last few thousands years reveals that during warm periods the average annual precipitation may diminish by 20% to 30%. In order to mitigate the impact of this decrease in precipitation, a national plan for desalination of sea and brackish water on a large scale must be adopted. At the same time the Coastal Plain aquifer has to be turned into a long term storage reservoire of second grade water. The development of "green energy" sources has to be given high priority.

References

Begin, Z. B., Broecker, W., Buchbinder, B., Druckman, Y., Kaufman, A., Magaritz, M. and Neev, D. 1985. Dead Sea and Lake Lisan Levels in the Last 30,000 Years: A Preliminary Report. Israel Geological Survey Report, 29/85, 1-18.

Bookman (Ken-or), R., Bartov, Y. Enzel, Y. and Stein, M. 2006 Quaternary lake levels in the Dead  Sea basin: Two centuries of research. Geological Society of America, Special Paper 401, pp. 155-170.

Frumkin, A. 1997. “The Holocene History of Dead Sea Levels” in The Dead Sea, TheLake and its Setting, eds. T. M. Niemi, Z. Ben-Avraham, J. R. Gat (Oxford University Press, Oxford, pp. 237-248

Frumkin, A., Kadan, G., Enzel, Y., Eyal, Y.  2001 "Radiocarbon chronology of the Holocene Dead Sea: Attempting a regional correlation", Radiocarbon,. 43. (3): 1179-1189,

Frumkin, A and. Elitzur, Y  2002 Historic Dead Sea Level Fluctuations Calibrated with Geological and Archaeological evidence" Quaternary Research 57, 334-342

Galili, E., Weinstein-Evron, M.  and Ronen, A. 1988. Holocene sea-level changes based on submerged archaeological sites off the northern Carmel coast in Israel. Quaternary Research, 29, 36-42.

 IPCC, (INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE) 2007 Climate Change 2007: The Physical Science Basis Summary for Policymakers, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Chang, IPCC Secretariat, Geneva. SWITZERLAND

Issar , A. S.  2003, Climate Changes during the Holocene and their Impact on Hydrological Systems, Cambridge University Press, Cambridge UK

Issar A. S. and Zohar, M. 2004,  Climate Change – Environment and Civilization in the Middle East, Springer –Berlin Heidelberg New York

Issar A. S. and Zohar M., 2007, Climate Change - Environment and History of the Near East, Springer –Berlin Heidelberg New York

Klein C., 1982, Morphological Evidence of the Lake Level Changes, Western Shore of the Dead Sea. Israel Journal of Earth Sciences 31:67-94

Nicholson, S.H., and Flohn, H. 1980, African Environmental and Climatic Changes and the General Circulation in the Late .i.Pleistocene; and .i.Holocene;. Climatic Change  2(4):313-348.

Pratt Report, 2004, Treatment and usage of brackish water The feasibility of desalination of local brackish/salty groundwater and wastewater treatment versus importation of desalinated seawater Beer-Sheva basin and the Negev Highlands.  ZIWR Unpublished Report

Raban, A. 1991. Evidence of sea-land vertical changes from archaeological sites. The Israeli Geological Society. The Geological Society Conference, Acar. April, 1991, Guide 4, 131-811 (in Hebrew).

Raban, A. and Galili, E. 1985. Recent maritime archaeological research in Israel—A preliminary report. The International Journal of Nautical Archaeology and Underwater Exploration, 14 (4), 321-356.

Ryan, W. and Pitman, W. 1998  'Noha's Flood. The new scientific discoveries about the event that changed history '     Simon and Scuhuster, New York, 319 p.