Environmental Impact of Multi-Annual Drought in the Jordan Kinneret Watershed, Israel
MOSHE INBAR * & HENDRIK J. BRUINS **
* Department of Geography, University of Haifa, Haifa, 31905, Israel
**Ben-Gurion University of the Negev, Blaustein Institute for Desert Research, Department Man in the Desert, Sede Boker Campus, 84990, Israel.
Abstract
Floods and droughts are most common among natural disasters, and the number of victims and economic damages are larger than those caused by other natural disasters like earthquakes and volcanic eruptions. The drought that affected Israel between 1998 and 2001 was of unusual climatic and hydrologic severity in the last 125 years in northern Israel. The climatic drought affected the water flow of the Jordan river and lake Kinneret level, which fell to –214.90m (below sea level), the lowest lake level in historical periods. The annual flow of the Jordan river in the drought period was the lowest in the 50 year hydrological record.
Human interference by water pumping and diversion exacerbated the negative drought natural impact, causing land degradation such as the drying of wetlands and salinization of freshwater aquifers. The failure to introduce drought contingency planning and sustainable water resources management has so far affected agriculture and nature conservation.
Introduction
Floods and droughts are the most common in spatial terms among the diverse natural disasters. Moreover, they cause more victims and economic damage than earthquakes and volcanic eruptions (Inbar, 2001). Vulnerability to drought is increasing in many regions, as growing populations intensify the pressure on water resources. Prolonged droughts are a major factor in land degradation processes and they affect extensive geographical areas. As a natural hazard, drought may strike in any climatic region, but its occurrence is more frequent in regions with dry climate such as Israel (Bruins, 1993; Amiran, 1994).
Drought is a normal, recurrent feature of climate, resulting from a deficiency of precipitation over an extended period of time, usually a season or more (Wilhite, 2000). Droughts build up gradually and passively as the cumulative effect of below average precipitation in a given area during a certain time period. Drought has both temporal and spatial dimensions, but boundaries may be fuzzy. Although the beginning and end of a drought is not always easy to determine, they have to be clearly defined (Wilhite and Glantz, 1985), in order to enable feasible management within an administrative governmental framework. The World Meteorological Organization defines a drought as a period of two consecutive years in which precipitation is less than 60% of normal in an area covering at least 50% of a geographical region (WMO, 1978). A definition of drought should be specific for each region in relation to its impact and management.
Droughts are among the most expensive disaster. The global economic losses from natural disasters increased from US$ 5 billion in the 1960s to more than US$ 50 billion in the last decade of the 20th century (Fig.1); (Munich Re, 2000). The 1988 drought in the western United States was the costliest natural disaster in US history for the time-range considered and its impact is likely to continue. During the 2002-growing season drought in Texas caused severe damage to agriculture, resulting in financial losses estimated at $316 million (Fannin, 2002).
Natural drought is a prevailing hazard in the Near East (Bruins, 2000). The available resources of fresh water in Israel are rather small in comparison with most other countries in the Near East (Table 1).
This study deals with the issue of drought in Israel in relation to land degradation and water resources management in the watershed of the Jordan River and Lake Kinneret. The effects of prolonged droughts in the Lake Kinneret watershed, which is by far the most important source of surface water in Israel, are examined. After some rainy years the public as well as decision-makers tend to forget the hazard of drought and the importance of assessing the effects of such major event.
Background to Droughts in Israel
The climate in Israel covers all the dryland zones – hyper-arid, arid, semi-arid and sub-humid (Unesco, 1979; Middleton and Thomas, 1992; Bruins and Berliner, 1998), as defined by the P/ETP index (P = precipitation and ETP = potential evapotranspiration). The average rainfall in the northern basin of the River Jordan is 700 mm and the potential evapotranspiration reaches 1600 mm; the P/ETP ratio is therefore 0.41, being in the semi-arid range. Only in the high mountainous areas of the Jordan River catchment rainfall is more than 800 mm and this region is sub-humid to humid ( Fig. 2). Interannual rainfall variations in the region are quite large, which is not surprising in view of Israel position at the northern transition of the largest planetary desert belt on Earth.
In terms of economic losses droughts form a major component- about 30%- of natural disasters in Israel Floods did cause extensive damage during the period 1948-1998 (Inbar and Agami, 1998), but the direct and indirect costs of prolonged droughts in Israel during the period 1998-2001 can probably be regarded as the major natural disaster in recent years, affecting both its water resources and its agricultural economy.
Meteorological conditions during drought periods in Israel are often characterised by a northward shift of the depression tracks and/or a decrease in the number of depression systems in the eastern Mediterranean region. These systems move generally from west to east over the Mediterranean Sea. The northward shifting of depression systems may be regarded as a symptom rather than a cause of the scarcity of precipitation in this region. The westward shifting in the atmosphere of the major upper level trough, on mean 500 mb charts, or its abnormal deepening leads to persistent dry and warm south-westerly upper flows which are the main reasons for the deflection of rain bearing depressions to the north-east (Levi, 1963).
Drought in Israel is characterised by low precipitation in the winter rainy season. However, sometimes it does not cover the entire country. For example during the 1931/32 rainfall season, the average annual rainfall in the semi-arid to sub-humid centre and north of Israel was more than 20% below the average, while the Negev in the south received rainfall above the annual average amount (Ashbel, 1950).
Droughts in Israel during the last 150 years
In the last 150 years, there have been three consecutive drought years for every 50 years period, according to the long term rainfall measurements series of Jerusalem (since 1846), Shechem-Nablus (since 1922), Beyrouth (since 1876), Kfar Gil’adi (since 1921) and other stations for recent periods of 50 to 60 years (Table 2). The average standard deviation was determined for consecutive multi-year drought (Figs. 3,4). The longest consecutive drought period was for six years from 1956/57 to 1961/62.
An evaluation of rainfall variability in Israel was made in relation to drought (Bruins, 1999). According to Amiran (1994) the average rainfall in drought years is 30-40% less than the long-term average. The overall average rainfall in Jerusalem for the period 1846-1993 amounts to 556 mm. The three wettest years during this period occurred in 1873/74 (1004 mm), 1877/78 (1091 mm) and 1991/92 (1134 mm). The three driest years occurred in 1950/51 (247 mm), 1959/60 (206 mm) and 1962/63 (227 mm), as noted by Amiran (1994).
Zangvil (1979) studied the Jerusalem rainfall record for the period 1846-1954. Applying a 10-year running mean, he distinguished a relatively wet period with above-average rainfall during 1868-1911 (690 mm) and a relatively dry period during 1912-1937 (412 mm). By evaluating individual precipitation years in relation to drought for Jerusalem during the period 1846-1993, Amiran (1994) distinguished six dry periods of three consecutive years or more in which at least one year shows a precipitation decline of more than 33% (Table 3).
Hydrologic drought in Israel, analysing 14 different streams in the central and northern part of the country over the period 1937 to 1984, was studied by Ben-Zvi (1987). The principal variables are (1) severity in terms of decline in water flow, (2) duration of hydrologic drought and (3) geographic extent. Severe and extensive hydrologic drought in Israel occurred in 1950/51, 1958/59, 1972/73 and 1978/79. These droughts affected the majority of the 14 studied streams. Continuous multi-annual shortages in streams occurred during the periods 1955-1961 and 1971-1979, albeit with variations concerning the beginning and end of those periods with respect to the various streams. A third multi-annual hydrologic drought period during 1967-1972 was limited to a few streams in central Israel.
The 1998-2001 drought period in the Upper Jordan watershed
The most extreme meteorological drought in northern Israel during the last 125 years was in fact the most recent drought of 1998/99-2000/01. This can be concluded from the long-term rainfall series of Beirut (Lebanon) and all the rainfall stations in northern Israel (Table 2). The average standardized value or relative deviation (z score) was –1.30 or 64% of the average rainfall for the 3-year period, the highest value in the recorded period. The second most extreme period was during 1931/32-1933/34 with a standardized value of –1.05 (Table 4). The rainfall in 1998/99 as recorded in Kfar Gil’adi was very low with 431 mm, which is only 53% of the average annual rainfall.
The mean annual volume of flow in the Jordan River is 399 x106 m3 and the standard deviation 142 x106 m3. The coefficient of variation is 0.26 ( Ben Zvi, 1987). An analysis of the Jordan River hydrological record shows that the 1999/2001 period was the lowest for a relatively prolonged period of three years (Table 5). The average standardized value for that period was –1.43, an extreme value as compared with former prolonged drought years. For a single year the highest standardized value was –1.62 for the 2000/2001 season or the last year of the period and not in the lowest rainfall year- 1998/1999. The lowering of the mountain water table during the three year period caused a reduction in the discharge of the springs that feed the river flow, and therefore the prolonged dry season caused the lowest water discharge at the end of the period.
The impact of the extreme 1998-2001 drought on Lake Kinneret
Lake Kinneret, the biblical Sea of Galilee, is a critical component of the integrated and centrally controlled water system of the Jordan River (Figs. 5,6). Lake Kinneret is situated in the Rift Valley and its water level at maximum capacity stands at -208.9 m (below sea level), above which flooding would occur in the town of Tiberias and other villages around the lake. The minimum acceptable level, the so-called red line, was set at -213 m. Pumping of water below that level might cause a severe deterioration in water quality of the lake, particularly in regards to salinity.
The Kinneret watershed area is 2730 km2 of which the lake covers an area of 170 km2, with a maximum holding capacity of almost 4,100 million m3. Each meter represents ca. 170 million m3 of water. An average amount of 450 million m3 used to be pumped from the lake annually. The overflow into the Jordan River at the southern end of the lake is controlled by a sluice gate in order to keep the lake level at desired levels (Grinwald and Bibas, 1989).
The main water diversion system of Israel is the National Water Carrier, completed in 1964, which draws annually about 300 million m3 of water from Lake Kinneret, eventually increasing to about 450 million m3 when the lake is full. In addition some 22 million m3 of saline water from springs are diverted around Lake Kinneret into the lower Jordan River. Following the peace treaty with the Hashemite Kingdom of Jordan, Israel now provides 50 million m3 of water yearly to Jordan from the lake sources. Lake Kinneret forms the pivotal part of the national water system, which also incorporates the Coastal Aquifer and Western Mountain Aquifer, and begins in the northwestern part of Lake Kinneret.
The only natural surface water reservoir in Israel, lake Kinneret, serves as the yearly storage of water received in its basin during the rainy season. In 1991, after three consecutive drought years, the water level fell to -213 m below sea level. The exceptionally wet year that followed in 1991/92 refilled the lake to its maximum storage capacity of -208.9 m. But during the severe three-year drought of 1998-2001 the water level fell to -214.90 m, the lowest lake level in historic periods (Fig. 7). Low levels have negative impacts on nutrient release, and beach resorts and touristic sites find themselves several hundreds meters from the shoreline. Hence the relationship between water quantity in the lake and water quality is becoming increasingly more precarious. It should be pointed out that the natural salt content of Lake Kinneret in the past was about 400 mg/l (or ppm), which is above the accepted national standard and World Health Organization guideline of 250 mg/l. However, the diversion of saline water from springs discharging into the lake brought down the salinity to acceptable levels, between 205 to 230 mg/l, considered to be a remarkable achievement (Ministry of Agriculture, 1973; Grinwald and Bibas, 1989; Bruins, 1993).
The combined effect of water pumping and drought led to a decline in lake levels. Salinity increased during low lake levels from 200 ppm of chlorides to 280 ppm. The Jordan river water flowing into the lake contains by comparison only 20 ppm of chlorides. Although a salinity of 280 ppm chlorides can be tolerated for domestic and some agricultural uses, it is considered high for irrigation of citrus groves and subtropical fruits. Such irrigation water also causes soil degradation by increasing soil salinity. Partially treated domestic sewage water, also used in agriculture, has an even higher salinity content of about 400 ppm chlorides. The recent appearance of the blue toxic alga Aphanizomenon ovalisporum, previously unknown in the lake, may indicate deterioration of water quality (Hadas et al, 2002). Low levels of Lake Kinneret also have a negative impact on nutrients release from the lake bottom sediments. (Fig. 8).