Here is what NASA came back to me with: "Unfortunately, it is doubtful that Aquarius (or any salinity-measuring satellite (SMOS, SMAP)) will be of much help in this because none of them work very well near land. About the closest Aquarius measured to a coast was on order of a 100 km. SMOS/SMAP might do a little better, but none are resolving within a kilometer or two of land masses. The issue is related to how they are detecting salinity, and the fact that land is so much brighter in the microwave region than seawater. However, even if they could work near land, which it is doubtful will ever be possible (and will certainly never be possible with the remaining salinity satellites (Aquarius failed in 2015)), there are some other problems with what you suggest. The amount of water being withdrawn per day is tiny compared to the total volume it is being withdrawn from, so even if all the rejected brine is being put directly back in the ocean, the resulting increase in salinity would not be detectable. (To put this in numbers, they withdraw about 3.3x106 m3/day of seawater. Assume the Saudi coastline is about 3x106 m long, the intake is 2 km offshore and the average depth is 1 km. That gives 6x1012m3 of volume to take seawater from, meaning the total possible increase in salinity is around 0.5 parts per million, or about 17x10-6 psu. On a good day, with a well-calibrated thermosalinograph, I might be able to resolve 0.001 psu changes, a salinometer could do better, maybe 0.0001 psu, but a satellite can detect changes on order of 0.01 psu. It is not clear that the Saudis are putting the rejected brine directly back into the ocean, but even if they are its density will make it sink to the bottom and not mix with the surface water. Therefore, there wouldn't necessarily be an increase in surface salinity. A long enough time series from satellites to detect the change isn't available, and likely never will be. To see these changes, you would need a time series going back before large-scale desalinization was being done, and stretching out for decades. Probably the changes in salinity due to changes in evaporation will be larger. The Red Sea, for instance, has a salinity of nearly 40 psu, which is 10% higher than water in the open ocean. Any changes in surface salinity in the Red Sea would have to be decoupled from changes in climate. That would be very hard to do in a coastal region. What you need is access to data from a long-term insitu measurement program where they looked at salinity over a decade. There are ocean monitoring programs being done out of KAUST, but I have little detailed knowledge of them, or who you could talk to to access their data."
Published by Dan Grech, Director at Global OTEC Resources
Here is what NASA came back to me with:
"Unfortunately, it is doubtful that Aquarius (or any salinity-measuring satellite (SMOS, SMAP)) will be of much help in this because none of them work very well near land. About the closest Aquarius measured to a coast was on order of a 100 km. SMOS/SMAP might do a little better, but none are resolving within a kilometer or two of land masses. The issue is related to how they are detecting salinity, and the fact that land is so much brighter in the microwave region than seawater. However, even if they could work near land, which it is doubtful will ever be possible (and will certainly never be possible with the remaining salinity satellites (Aquarius failed in 2015)), there are some other problems with what you suggest.
The amount of water being withdrawn per day is tiny compared to the total volume it is being withdrawn from, so even if all the rejected brine is being put directly back in the ocean, the resulting increase in salinity would not be detectable. (To put this in numbers, they withdraw about 3.3x106 m3/day of seawater. Assume the Saudi coastline is about 3x106 m long, the intake is 2 km offshore and the average depth is 1 km. That gives 6x1012m3 of volume to take seawater from, meaning the total possible increase in salinity is around 0.5 parts per million, or about 17x10-6 psu. On a good day, with a well-calibrated thermosalinograph, I might be able to resolve 0.001 psu changes, a salinometer could do better, maybe 0.0001 psu, but a satellite can detect changes on order of 0.01 psu.
It is not clear that the Saudis are putting the rejected brine directly back into the ocean, but even if they are its density will make it sink to the bottom and not mix with the surface water. Therefore, there wouldn't necessarily be an increase in surface salinity.
A long enough time series from satellites to detect the change isn't available, and likely never will be. To see these changes, you would need a time series going back before large-scale desalinization was being done, and stretching out for decades.
Probably the changes in salinity due to changes in evaporation will be larger. The Red Sea, for instance, has a salinity of nearly 40 psu, which is 10% higher than water in the open ocean. Any changes in surface salinity in the Red Sea would have to be decoupled from changes in climate. That would be very hard to do in a coastal region.
What you need is access to data from a long-term insitu measurement program where they looked at salinity over a decade. There are ocean monitoring programs being done out of KAUST, but I have little detailed knowledge of them, or who you could talk to to access their data."