Anthropogenic drought dominates groundwater depletion in Iran
SamanehAshraf1 , Ali Nazemi1* & AmirAghaKouchak2
Using publicly-available average monthly groundwater level data in 478 sub-basins and 30 basins in Iran, we quantify country-wide groundwater depletion in Iran. Natural and anthropogenic elements afecting the dynamics of groundwater storage are taken into account and quantifed during the period of 2002–2015. We estimate that the total groundwater depletion in Iran to be ~ 74 km3 during this period with highly localized and variable rates of change at basin and sub-basin scales. The impact of depletion in Iran’s groundwater reserves is already manifested by extreme overdrafts in~ 77% of Iran’s land area, a growing soil salinity across the entire country, and increasing frequency and extent of land subsidence in Iran’s planes. While meteorological/hydrological droughts act as triggers and intensify the rate of depletion in country-wide groundwater storage, basin-scale groundwater depletions in Iran are mainly caused by extensive human water withdrawals. We warn that continuation of unsustainable groundwater management in Iran can lead to potentially irreversible impacts on land and environment, threatening country’s water, food, socio-economic security.
By suppling ~ 36% of drinking water and ~ 42% of agricultural water, groundwater is a key freshwater resource globally1,2 . During the current state of “Anthropocene”, groundwater reserves are under enormous stress due to both natural and anthropogenic pressures3,4 . Naturally, groundwater is sensitive to variability and change in hydroclimatic conditions5–7 . For instance, increased evaporation due to a warmer climate reduces groundwater recharge8 , which is also sensitive to landscape features, such as vegetation and soil characteristics9,10. In parallel, groundwater availability is also afected by human water withdrawals to support various socio-economic activities11. Uptakes from groundwater reserves have increased substantially in recent years due to ever-increasing global population and water use per capita12. Despite current pressures on groundwater resources, they have a critical role in maintaining water security. Currently one third of the world’s population living in water-stressed regions13, particularly in semi-arid and arid regions of Asia, the Middle East and North Africa as well as the Mediterranean countries. In many parts of these regions, groundwater is the only reliable source of water; because surface water is seasonally or permanently absent14. As water demands in these regions are mainly concentrated around food productions—e.g.,~85% of water use in the Middle East is exclusively used for irrigation15—groundwater availability and food security become massively intertwined and are linked to national and regional security16. Te availability of groundwater resources becomes more critical in a warmer and more populated world17–19, as surface water resources deplete even more under increasing temperature20–22, causing elevated competition over the remaining surface water resources15,23–26. Although accurate monitoring of groundwater resources is essential for provision of efective management practices27, groundwater monitoring has not well-attended in developing countries28, mainly due to the hidden nature of groundwater and the lack of recognition for the human impacts on groundwater resources29. Data coming from the Gravity Recovery and Climate Experiment (GRACE) satellite has provided a grand opportunity for monitoring changes in groundwater storage and detecting depletion at larger scales30–32; however still the value of in-situ groundwater monitoring is unquestionable, particularly at smaller basin and sub-basin scales. Here, we focus on Iran, a country where natural dryness is mixed with rapid socio-economic development, growing water demand particularly for agriculture, and unsustainable land and water management25,33. We analyze the dynamics of Iran’s groundwater resources using the publicly-available data for average groundwater level at basin and sub-basin scales, published by Iran’s Ministry of Energy. Te unique feature of our study is in quantifying the variation in groundwater storage and its dependencies with potential natural and anthropogenic drivers solely based on basin and sub-basin estimations for natural and anthropogenic drivers of groundwater dynamics, extracted from country-wide networks of in-situ observations. Tis allows extracting a set of ground truths for causes of groundwater depletion, and to determine the potential impacts of groundwater depletion on water, land and environment at basin and country-wide scales.
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