Well,

Remotely sensed images in different periods, /or elevation differences related to the triangulation point.

Regards

Land subsidence is most often caused by human activities, mainly from the removal of subsurface water. Here are some other things that can cause land subsidence: aquifer-system compaction, drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, and thawing permafrost.

Land subsidence can significantly increase soil water evaporation and infiltration and decrease the clay and silt contents of soil, leading to an SWC reduction and accelerating soil drought, salinization, and desertification, particularly in arid and semi-arid areas.

Measuring and Monitoring: Elevation or elevation-change measurements are fundamental to monitoring land subsidence and have been measured by using interferometric synthetic aperture radar (InSAR), continuous GPS (CGPS) measurements, campaign global positioning system (GPS) surveying, and spirit-leveling surveying.

From USGS

Measurements of land-surface elevations, aquifer-system compaction, and water levels are used to improve our understanding of the processes responsible for changes in the elevation of the land's surface. Elevation or elevation-change measurements are fundamental to monitoring land subsidence and have been measured by using interferometric synthetic aperture radar (InSAR), continuous GPS (CGPS) measurements, campaign global positioning system (GPS) surveying, and spirit-leveling surveying. Aquifer-system compaction is measured by using extensometers; these measurements have the added benefit of being depth-specific because extensometers are anchored at specific depths of interest. So, while each extensometer measures some fraction of total subsidence, the measurements can help us better understand the depths at which compaction is occurring. The most precise measurements tend to be made using spirit-leveling surveys and extensometers. The least precise measurements tend to be made by using GPS surveying, with CGPS and InSAR measurements falling somewhere in the middle with regard to preciseness.

Please, refer to the following link :

https://ca.water.usgs.gov/mojave/mojave-land-subsidence.html

Regards

Aerial or ground based LiDAR may be helpful if you have specific study areas, and can retake survey areas through time. Under some geologic conditions as karst terrain, land adjustments or sinkholes can be natural, and sometimes induced due to surface changes in land use or activities. Withdrawal of water, oil, or mining of substrate could contribute. Desertification and land degradation can also result from land abuse and excessive vegetation removal, and failing to return native cover types. As suggested by others, there are ways to study this phenomenon, specific to your area of interest. Modifying the local hydrology can funnel stormwater to unstable karst areas, and heavy equipment vibrations and some land uses can also compact soils and alter underground flow patterns. Poor farming and grazing practices can eventually alter land productivity, contributing to vegetation loss, erosion and gullying. In piedmont SC, USA, the effects of past farming practices took many decades of land abuse before erosion removed the A horizon and locally B horizon, exposive the highly erosive saprolitic materials that developed into gullies and land barrens. Likewise the native prairies in western US took years of past farming and overgrazing to cause severe vegetation loss, erosion and in some instances leading to desertification. Many other countries like the US have learned lessons from poor soil and water conservation awareness and practices. So a key point might be to recognize the sensitive land, activities and symptoms before failure or degradation occurs.

Dear Bayan Hussien

Thank you for your participation in this discussion.

Dear Prof Bachir Achour

thank you so much for your detailed answer and as well as introducing scientific references for the subject. As far as I know In the 1980 th decade, the highest rate of land subsidence occurred in Western American countries such as California. Scientists have been working to identify, control and manage it after understanding how the Earth's subsidence has shaped its future effects and implications. Their first action was to relocate inter-basin water. For example, with the redirection of the Colorado River to California, they were able to somehow overcome the phenomenon of land subsidence in Western America at that time, but I think that with the passage of time and with the drought, water from California would no longer enter California.

Dear Mr. William F. Hansen

thank you very much for your detailed answer.

From in point of view desertification, in these areas, subsidence means the discharge of underground aquifers and the advance of saline water to freshwater aquifers and the pumping of saline water from the ground leading to saline soil on the ground.

In this phenomenon, vegetation types whose plants are saline and shallow-rooted also reduce the volume of water in the underground aquifers and drop in water level, limiting root access to water and thus reducing the canopy area. . Continuing to do so, and in such productive agricultural areas, can become a real desert.

The following paper contain excellent information, please see the following link:

Article Soil-Related Sustainable Development Goals: Four Concepts to...

I believe in a strong positive relationship, the more one increases, the other increases strongly

Dear Colleagues:

Subsidences are the most common results of extractions of solids and liquids from the subsurface irrespective of the existing climate. Exploiting mineral or coal deposits causes mining subsidence at the surface depending upon the mining technique used and the size and shape of the underground galleries, stopes and tunnels. Solution mining of, e.g., salt gives rise to collapses and natural immigration of surface water will have the same effect in carbonate and sulfate karst. The process may be called subrosion. The most serious one entirely man-made is an unbalanced harvesting of groundwater. Rocks consist of solids (minerals) and pore-filling gases and liquids. If you extract them in a disproportionate way the rock collapses leaving behind subsidences. Large cities in Germany have been the culprits of such subsidences and in the last consequence it will also impact on the pedosphere and the biosphere (flora). The climate is not the culprit but only a kind of “lubricant” accelerating the effect, particularly in arid and semiarid climate zones where replenishment is low or nil and only fossil water reservoirs are tapped in.

Kind regards HGD

Dear prof HGD

Thank you very much for your scientific and detailed answer.

Dear Shaki Tuleab

Thank you for your participation in this discussion.

According to our global research about Land Subsidence "Land Subsidence: A global Challenge" The drivers of the LS could be divided into two general categories human-induced factors including fluids extraction from subsurface layers (e.g. water, oil, and gas), land-use change (e.g. load of man-made constructions), construction of underground facilities and mining and ii) natural activities including fault, tectonic movement, consolidation/compaction of recent deposits, the collapse of loess, sea-level rise, oxidation and drainage of organic

soils, karst erosion, and permafrost degradation. Both drivers (natural and human) are distributed around the world. Based on the considered studies, the natural and human-induced factors are responsible for 23.08% and 76.92% of the LS occurrence, respectively. So, the role of land use changes is 8.97 %. for finding more information, you can see the article.

Dear Dr. Bagheri

Thank you very much for your detail reply