Background/Objectives
‘‘As every day brings urgent reports of growing water shortages around the world, there is no time to lose in the search for solutions” (Siegel, 2015). In coastal areas, such as the Levant, seasonal transformations of the heat content of adjacent seas can be an important factor in the local weather and precipitation. Winter storms generated over the Mediterranean Sea carry moisture towards the continent where the moisture precipitates as rain. A relatively warm sea during the wintertime is the source of heat energy for intense evaporation from the sea surface. The amount of heat stored in the sea during the previous summer is the major energy source for the winter storms that spread precipitation over the Levant. There is a high correlation (~90%) between the heat energy extracted from the sea and the precipitation for the corresponding period from November-December to March-April. Based on this multiyear observation, Bronicki and Assaf (1980) proposed a method to store additional heat in the upper layer of the Mediterranean Sea during the summer by increasing mixing in the upper layer of the sea with an artificial upwelling (bringing cold water from deeper layers) using wave-driven pumps. The increase of the precipitation by 10% over the Levant can be achieved by deploying 5,000 wave-driven pumps working in the artificial upwelling regime along about 100 km of coastline on the Mediterranean Sea. This approach is associated with significant deployment and maintenance costs, and it creates a problem for navigation. Furthermore, the additional heat accumulated in the upper layer of the sea will be carried away by surface currents, which can reach 1 knot in the upper 50 m to 100 m layer of the sea in this area.
Approach/Activities
Based on the analysis of the oceanographic conditions in the Levant area, Soloviev and Dean (2000, 2022) have proposed a different technological approach—artificial downwelling, which can increase the heat storage rate by two orders of magnitude and correspondingly reduce the required number of wave-driven pumps to make the system realistic for practical application. Heat storage of the sea will be increased during the summertime by pumping relatively warmer surface water to the deeper layers with relatively cooler water. An ANSYS Fluent computational fluid dynamics model indicates that in locations where currents are minimal in these deeper layers, the lateral transport of the warmer water (introduced by wave-driven pumps and mixed with surrounding water by the density equilibration) will be minimized. During the winter season, this additional heat will intensify evaporation from the sea and, under prevailing winter winds from the sea to the land, will increase precipitation in the nearby continental zone.
Results/Lessons Learned
This “natural” desalination process using the energy of surface waves will bring additional freshwater to arid coastal areas during wintertime in the form of winter rains. In the long term, this system being installed offshore of the Israel coast of the Mediterranean Sea is expected to support green infrastructure in the arid and semiarid environments and advance agriculture, forestry, and farming in the Levant by increasing rain rates during the winter season. One advantage of this desalination approach (which can be called the “Natural Desalination Factory”) is that it is a “green” technology effectively using the energy of surface waves without any anthropogenic chemicals being added to the sea!