ABSTRACT
Groundwater in the Aral Sea Basin (ASB) is used as a rural water supply, for irrigation and as a supply for some major cities. Recently, groundwater use has been increasing due to growing demand in agriculture. Exploitation of aquifers is favored because of lower infrastructural investment in comparison to surface water use. The proportion of groundwater use in the ASB varies between countries. Tajikistan and Afghanistan are the largest groundwater users, with 19.7 percent and 15 percent, respectively, of their total country-wide annual water withdrawal; groundwater use in Turkmenistan is only 1.1 percent of the total national withdrawal. These numbers, however, show that the proportion of groundwater use of total use remains small within the Basin. In many regions, the seasonal variation of groundwater levels is linked to water consumption during irrigation season. Higher groundwater levels due to irrigation carry the risk of increased soil salinity. Reduced groundwater levels are a serious threat to ecosystems and are conducive to desertification. The impacts of land use change and climate change on groundwater are not well understood in the Basin at present. Groundwater recharge in the Basin seems to be reduced due to reduced soil moisture. Due to the lack of in-situ data on groundwater, the total water storage variation is estimated by remote sensing (GRACE). This indicates that the ASB is experiencing a total water storage depletion of −3.35 ± 0.45 mm/year. The depletion is largely due to an increase in evaporation rates and groundwater extraction given the fact that the average annual rainfall increased by 11 percent during the investigated period (2002–2017: 333 mm) compared to that of the previous two decades (1979–2000: 299 mm). Groundwater quality has deteriorated in many parts of the ASB where intensive irrigation for agricultural production takes place. This also occurs because drainage systems are no longer maintained, entailing salt depositions in the soil.
