The Red Sea is a narrow body of water formed within a deep rift valley separating the African and Arabian tectonic plates. The idea that the sea is “drying up” stems from visible signs of water loss and increasing salinity driven by the region’s intense climate. While the basin is not disappearing in a catastrophic sense, it is experiencing acute changes in its water balance and temperature profile. These accelerating changes, driven by external forces, significantly alter the sea’s unique hydrological properties. This fundamental shift in the environment has far-reaching consequences for marine life and human populations along its shores.
The Red Sea’s Unique Hydrographic Profile
The Red Sea’s hydrographic profile makes it sensitive to environmental shifts because it functions as a concentration basin. The volume of water lost through evaporation greatly exceeds the volume gained from rainfall and river runoff. The average rate of evaporation is extremely high, estimated at around two meters per year. This water loss is the primary driver of the sea’s naturally high salinity, which increases from south to north, reaching up to 41 practical salinity units (psu) in the northern gulfs.
The sea’s status as a semi-enclosed basin compounds its vulnerability because its connection to the open ocean is restricted. Water exchange with the Gulf of Aden and the Indian Ocean occurs only through the narrow Bab el-Mandeb Strait, which has a sill depth of approximately 140 meters. This limited opening restricts deep water circulation, creating an “inverse estuarine circulation.” In this circulation, fresher surface water flows in while denser, saltier water flows out underneath. This mechanism maintains the sea’s long-term salt balance, but the constriction makes the system slow to flush and highly susceptible to evaporation changes.
Current Status and Measured Water Loss
Despite the idea of the Red Sea “drying up,” satellite altimetry data reveals that the sea level is actually rising, though this points to significant stress. Between 1993 and the present, the sea level has been rising at an average rate of 3.88 millimeters per year, consistent with the global average. However, the period after 2000 shows an acceleration in this rise, with rates spiking to around 6.40 millimeters per year.
This sea level increase is primarily due to the thermal expansion of the water column, known as the thermosteric effect, caused by increasing temperatures. Sea surface temperature (SST) has been warming at an accelerated rate of 0.187 degrees Celsius per decade since 1985. This pace is nearly two and a half times faster than the global ocean average, indicating hydrological imbalance and stress on the basin.
Intensified warming drives an increase in surface evaporation, which contributes to higher salinity levels in the upper water column. While the sea is not physically shrinking, rapid thermal and haline changes fundamentally alter the water’s properties and density. This increase in salinity, coupled with rising temperature, represents the most significant manifestation of “water loss” regarding the sea’s environmental health.
Key Drivers of Environmental Change
The dominant factor accelerating changes in the Red Sea is global climate change, manifesting locally as enhanced surface evaporation. Increased atmospheric temperatures lead to a greater exchange of heat at the sea surface, driving up the rate of water vapor loss. The warming itself is largely driven by the advection of warmer water masses from the Gulf of Aden, rather than solely by a rise in local air temperature.
Seasonal monsoon wind patterns also influence the crucial water exchange at the Bab el-Mandeb Strait. These shifting wind systems determine the volume and properties of water flowing in from the Indian Ocean, directly impacting the sea’s internal circulation and salt balance. Any long-term shift in these regional wind regimes can exacerbate the water deficit caused by evaporation.
A significant, localized driver of change is the increasing reliance on desalination by the littoral states. Countries along the Red Sea coast, particularly Saudi Arabia, operate a high volume of desalination plants. These plants discharge hypersaline brine, a concentrated mixture of salt and chemicals, directly back into the sea near the coast. This localized discharge creates plumes of excessively salty water that can spike coastal salinity far beyond natural levels, threatening nearby marine habitats.
On a geological timescale, the Red Sea is an active area that continues to widen as the African and Arabian plates pull apart. Tectonic activity has historically caused extreme environmental events, such as the complete desiccation of the sea approximately 6.2 million years ago during a “salinity crisis.” While today’s changes are climate-driven, this history establishes the basin as uniquely prone to dramatic shifts in its water balance when oceanic connections are altered.
Ecological and Geopolitical Consequences
The rise in temperature and salinity poses an immediate threat to the Red Sea’s unique biological systems. The region is home to extensive coral reef ecosystems, known for a higher thermal tolerance compared to reefs elsewhere. However, this resilience is not infinite, and the rapid, sustained warming trend increases the risk of coral bleaching and disease outbreaks.
Localized spikes in salinity caused by desalination brine discharge also threaten coastal habitats. This stresses organisms that cannot tolerate the sudden change in water chemistry. The health of endemic fish populations and other marine life is directly linked to the stability of water temperature and salinity, making them vulnerable to accelerating environmental shifts.
The Red Sea is also a major geopolitical chokepoint, facilitating nearly 12% of global trade via the Suez Canal. Subtle changes in water density and temperature can affect the buoyancy and speed of large vessels, impacting the efficiency of this maritime traffic route. Environmental degradation threatens the resource security of bordering nations, which depend on the water for fisheries and desalinated drinking water. Disruptions to the sea’s stability carry global implications for trade and regional stability.