Water Resources has released a new set of maps tracking land subsidence issues throughout Arizona. The 55 new maps depict a continuation of established trends: The largest land subsidence rate remains in southeastern Arizona.

Regions of the Willcox Basin, where agricultural activity remains largely groundwater-reliant, has seen subsidence rates of 15 centimeters per year. The new maps also depict subsidence on the order of 10 centimeters annually in the Douglas Irrigation Non-expansion Area.

As explained in the Hydrology section of the Department’s website, subsidence occurs when water tables decline:

“Land subsidence in the basins of Arizona is generally due to compaction of alluvium caused by lowering of the water table. As the water table declines, pores in the alluvium once held open by water pressure are no longer supported and collapse. Collapse and subsequent lowering in elevation of the land surface is defined as land subsidence. This subsidence is generally not recoverable. If this subsidence occurs over areas of bedrock, differential subsidence can occur.”

Arizona Department of Water Resources and their partners in the Arizona Land Subsidence Group are national leaders at employing state-of-the-art subsidence-detection technology to track changes in land surface elevations.

Specifically, the group has deployed Synthetic Aperture Radar (SAR) and interferometric processing (InSAR) to detect those changes.

The 55 new maps cover a variety of different land-subsidence features and time periods. In all, the Department’s library includes 450 subsidence maps. Users are able to navigate to each individual land-subsidence feature here.