Abraham J. Melloul and Martin. L. Collin
Israel Hydrological Service, Israel

The word "drought" is noted in the Bible in the context of many historical events. The Hebrew word "batsoret" can be variously translated as "drought", "rock", "tightness", "problem", as well as "activity of autumn grape harvest". All can be related to water and agriculture, but also to the environmental and spiritual factors which characterize a drought season. In Israel, during normal years, an average of around 1.2 billion cubic meters of groundwater are abstracted by wells. Approximately 70 per cent of these pump the Coastal and the Yarqon-Taninim aquifers.

During the current hydrological drought year in Israel, rainfall reached only around 30% of the multi-annual average value. No significant contribution was made to the surface water system, nor to aquifer recharge. However, despite restricted agricultural usage, more water is required. During this drought year, groundwater abstraction from the two major groundwater basins increased around 20 % over the previous year. As a result, groundwater systems suffered a sharp water level depletion. Decline in the Yarqon-Taninim aquifer was sharpest (Melloul, 1999). The objective of this paper is to note the adverse hydrogeological effects generated, as well as environmental impact due to groundwater depletion.

Hydrological Factors: Analysis of Israel Hydrological Service data concerning the Coastal and the Yarqon-Taninim basins indicates that water tables dropped at the end of summer 1999 under "red line" levels utilized as early signals. Groundwater depletion lead to significant cones of depression, concentrating build-up of salinity and pollution. Near the coast, low water levels induced seawater intrusion, increasing groundwater salinity. This caused aquifer media to become impervious in certain cases (Goldenberg et al.,1986). Increasing salinity lead to fresh water reserve depletion. Curiously, a drop in chloride content was noted in some wells between 1998 and early 1999. This could be indicative of abstraction of water from the aquifer's deeper fresh layers.

Environmental effects and soil and unsaturated zone salinity: Currently, agricultural irrigation consumes around 60% of fresh water available in Israel. To reduce excessive agricultural water use, effluents are increasingly used for irrigation. Currently, domestic effluents from all three major metropolitan areas in Israel produce well-treated water for irrigation. However, local settlements apply their own effluents for irrigation of their fields, and these effluents receive only primary treatment previous to their application to the ground surface. High temperatures lead to evaporation from plants, and the soil surface becomes increasingly saline. Pollutants deposited on the surface are neither flushed nor drained during such periods, so that they accumulate on and in soils and in the aquifer's unsaturated zone. Not until the initial autumn rain of a season following a drought year would these salts be flushed from the soil and unsaturated zone (Melloul and Goldenberg, 1993).

Lack of water turns free-flowing streams into dry wadis and depletes natural reserve ponds of fresh water, killing off plant and animal species. Lowered water tables alter lake and stream banks away from water-side residential hotels and homes. Fish colonies and ancillary economic activity can be impacted. Desertification is enhanced, especially along the borders of semi-arid regions and true deserts. In such places, a decreased water supply can be synonymous with environmental "death".

Considering the likelihood of further and even more severe droughts, several concerns must be confronted. These include whether adverse effects will be short- or long-term, whether the effects will be irreversible, and the measures required to mitigate impact of coming droughts.

Recommended measures regarding future drought years: Remediation efforts to prevent desalinization and desertification During a drought, the process of salt accumulation is enhanced. Desalinization measures become especially critical. These can involve treating polluted effluents, import of fresh water from outside sources - including seawater desalinization, and reduced abstraction in critical areas. In drought years, desertification can be fought most effectively by employing "drought agriculture", agriculture based upon crops having low sensitivity to salinity, and which can be readily irrigated with treated effluents. Especially in drought years, special care must be taken to restrict use of improperly treated effluents, which can negatively impact human health and the soil. Effluents to be used for irrigation must be given the highest level of treatment.

An adequate monitoring network must enable accurate definition of the current situation. This has to enable to provide: trends in soil and unsaturated zone pore water quality, groundwater quantity and quality trends and , "red lines". These "red-lines", must reflect not only the specific localities situation within an aquifer, but they have also to adequately reflect the situation for the entire reservoir. Therefore, monitoring data must supply a global perspective of the aquifer's true situation. The objective being to provide optimal and rational management in such extreme cases as drought years.

To preserve every drop of rain and dew that falls, proper management must consider information regarding probable extreme climatic situations. This can be extracted both from recent drought year data and from historical records. For instance, this can include looking to the skills of the Nabathean civilization of the Negev desert 2,000 years ago, whose expertise involved conserving what little rain and dew was available in that region, in order to enable a true flowering of their settlements.

Lack of rainfall is not the sole parameter when defining the term "drought". Other considerations include recharge of an aquifer's water quantity and quality, minimum water capacity required for supplying basic agricultural and drinking needs, price, as well as maintaining the confidence level of the regional population that their supply of water will fulfill their usage requirements.

During a drought, information and education are essential for the population's psychological preparation in order to maximize their participation in remedial activities. The objective is to promote constructive social behavior to minimize adverse drought effects upon the economy and public health. International coordination should be properly orchestrated so as to promote effective and early preparation through collaborative activity.