Sum the three site gains the team reports and you get 13.41 square kilometres of new salt flat, about 0.27 square kilometres a year over the fifty-year window [15][16]. Nearly two thirds of that, 63%, sits on the Diib fan alone [17]. The concentration is worth pausing on, because Diib is the one site where the described process is not brine arriving from below. That fan is built by a wadi draining 42,000 square kilometres from central Sudan to the coast, dumping sand and silt into a delta that wind and tide keep reworking [11]. A prograding delta and a salt margin creeping inland under a rising water table both register as more sabkha in a satellite classification, and only one of them is a sea-level signal. The site-level numbers carry more information than the collective figure [2].
That percentage also arrives without its denominator. If the fourth site, Bir Shalatein-Marsa Himeira, added little, then 13.41 square kilometres amounting to roughly 12% puts the combined 1973 footprint near 112 square kilometres [18]. That is an inference from the reported numbers rather than a measurement the article states, and it is the quantity you would want in hand before judging whether 12% in five decades is fast.
Evaporation of 28 millimetres a day is a summer peak [13]. Sustained for a month it would remove 840 millimetres of water [19], which is the right frame for how fast a crust forms and the wrong frame for an annual water budget. The colour zoning at Bir Shalatein maps that gradient directly, white crusts where evaporation works hardest and darker mud and algal mats where the ground stays damp [10].
The claim that these flats function as recorders rests on the stratigraphy more than on the area trend. Pits at Marsa Abu Madd show tidal deposits from wet phases interleaved with windblown sands from dry ones [8]. That is a system with a history of swinging in both directions, well before anyone was watching it from orbit, which argues against reading the 1973 to 2023 expansion as necessarily monotonic.
What the work does not measure is the part an engineer would ask for first. There is no subsidence figure here, no bearing capacity, no groundwater salinity time series; the attribution to rising sea level and intensifying aridity rests on those forces co-occurring with the observed growth rather than on a measured local trend [12]. The pits had to be dug with brine in mind [9], which tells you the water table is shallow and says nothing quantitative about how shallow.
My read: the durable output of this study is the fault map at Ras Baghdadi, where fractures running in several directions draw seawater inland to meet runoff from the mountains [7]. Area statistics tell you the margin moved. Faults tell you where the brine goes next, and that is the layer worth having before the resorts arrive on a coast where these four sites are currently the undeveloped exception [14].
