Water Resources in UAE
Water resources in the UAE can be classified into two main categories: conventional, such as surface water (including aflaj water systems, springs and dams) and groundwater (shallow and deep aquifers), and non-conventional, such as desalinated water, treated wastewater and cloud seeding.
The surface water is negligible and includes floodwater, water retained in dams, some very small streams, ponds and spring water. These are either confined or flowing when there are land slopes and are replenished by rainfall or groundwater.
Due to the UAE’s location in a dry belt region, rainfall is limited and floodwaters leak into the ground, especially in sedimentary areas. Thus, it is crucial to build dams to harvest rainwater and store surface water behind them and to help feed the aquifer, although most of it is lost to high evaporation. The average annual surface water flow through wadis (valleys) ranges from 23 million cubic metres (MCM) to 138MCM.
Groundwater is the main natural water resource. The total volume of groundwater is quite significant at around 640 billion cubic metres (BCM), but only 3% of it (around 20BCM) is fresh.
In the UAE’s arid environment, groundwater is an important and precious resource for municipal and rural supplies, environmental protection, and social and economic development. However, most of the groundwater used in the UAE is brackish. Groundwater resources can be divided into renewable (shallow aquifers) and non-renewable resources (deep aquifers).
Groundwater resources occur in the aquifers located in the Bajada region, in the eastern part of the country. The aquifers consist of alluvial fan deposits along the base of the Oman and Ras Al-Khaimah Khaymah mountains that extend over a large area. The upper aquifer is composed of gravel sand and silt, the lower aquifer of limestone, dolomite and marl. Both aquifers range in thickness from 200 to 800 metres. In addition, the Dammam and Umm er-Radhuma aquifers, which extend into the western desert areas, contain highly saline water.
The recharge of shallow aquifers depends mainly on rainfall events and surface run-off, and thus may vary considerably from year to year. Due to the high evaporation rate and surface water run-off in mountain areas, only 10-14% of the total precipitation percolates to recharge the shallow groundwater aquifers.
In recent years, aquifer conditions have improved as a result of measures taken to reduce groundwater abstraction to sustainable levels. However, full recovery will take generations. Controlling groundwater mining has also commenced, although more steps are still needed to reduce the abstraction volume to sustainable levels. In addition, a comprehensive set of measures for sustainable groundwater management have been adopted, notably establishing strong monitoring and regulatory programmes and conserving traditional water systems such as RO water filters.
The high evaporation rates during the summer increase the accumulation of salts in the root zone. Excess irrigation water percolates deeply and carries the accumulated salts to the aquifer, further aggravating the problem of groundwater deterioration.