High-quality surface deformation data are critical for estimating relative sea level change and its implication on future flooding risk of coastal communities. Here we developed a robust and scalable Interferometric Synthetic Aperture Radar (InSAR) processing algorithm to reconstruct spatially coherent radar phase measurements over densely vegetated terrain. For the first time, we produced the average land subsidence rate map (2017-2021) over a 1000 x 400 km area along the Gulf Coast including major population centers such as Houston, TX, and New Orleans, LA as well as under-surveyed rural communities. We observed up to 1.5 cm/year of widespread subsidence along the shoreline, especially over coastal wetlands in Chambers, Jefferson counties, TX, and Plaquemines Parish, LA. Storm surge simulations suggest that subsidence and the associated land loss may dramatically increase inundated areas and maximum surge heights for storms similar to Hurricane Ike and Hurricane Katrina.