New estimation of Nile Delta subsidence rates from InSAR and GPS analysis

Increase of water level in most of the world's oceans and seas, including the Mediterranean, due to global warming may have a serious impact on the Nile Delta. The Nile Delta is considered as one of the most important regions in Egypt as more than 50% of the Egyptians are living there. To study the thread of a potentially sinking and flooding of the Nile Delta, here, we estimate present vertical motion by use of the Persistent Scatterer InSAR (PSI) analysis in addition to the available GPS stations in the Nile Delta. The subsidence rate of the Nile Delta is estimated by applying the PSI processing for all archived Envisat SAR data from the descending tracks 207 and 436. From these tracks, 36 and 37 SAR scenes were collected, respectively. Moreover, the results of a time series analysis for six GPS permanent stations in the Nile Delta were used to validate the estimated subsidence rates from PSI analysis. The PSI and GPS solutions show that the estimated ground deformation is strongly localized at the big cities. From time series for selected PS pixels from Cairo, Tanta, Mahala, Mansoura, Damietta, and Port Said, the estimated subsidence rates from Envisat scenes are around -6.4 +/- 0.4mm/year, -4.0 +/- 0.6mm/year, -4.8 +/- 1.0mm/year, -10.0 +/- 1.2mm/year, -10.3 +/- 1.6mm/year, and -4.9 +/- 1.6mm/year, respectively. The localization of subsidence rates at big cities implies that the detected signals may be due to human activities, such as ground water pumping, and that the Delta as a whole presently is not subsiding.