Pezhman Tahmasbi, University of Colorado Professor: Iran is in a 'dangerous' situation regarding land subsidence

Pezhman Tahmasbi, an Iranian professor at the Colorado School of Mines, stated in an interview with Voice of America that the situation of land subsidence in Iran is 'dangerous' and that Iran ranks at the top of all criteria considered for comparing different countries in this regard. He emphasized the need for a precise map to identify vulnerable areas. However, there is insufficient global research, and existing maps either do not provide information on the magnitude of subsidence or are limited to regional scales. A number of scientists from the Colorado School of Mines have introduced the first global map of subsidence rates using modern data-driven modeling techniques, which can be used to inform and determine groundwater management policies. Pezhman Tahmasbi, one of the authors of this study, told Voice of America, 'Based on the results we gathered from very comprehensive data worldwide, we can say that Iran is in a dangerous situation and ranks at the top of all the criteria we selected for comparing different countries.' He explained that this study considered '23 variables,' including groundwater, climate, geology, and topography, based on processed data available. Tahmasbi stressed that these results could change with the inclusion of more accurate data, such as remote sensing data, but processing them is very costly and time-consuming, so they only had access to some processed data in Iran. Nonetheless, he stated that even with such data added, it is unlikely that the overall trend shown in this map would change. The scientists identified a significant positive relationship between the amount of groundwater extraction and subsidence, meaning that these areas should be the main focus of water resource management to mitigate such risks. Tahmasbi said the goal of this study is to raise awareness about the important parameters that they believe can affect subsidence. He added, 'Among these parameters, groundwater extraction is the main variable. Some other parameters, such as soil type and topography, are beyond our control, and one of the parameters we can control is groundwater extraction. Iran has depleted most of its aquifers due to adopting some radical and unmanageable strategies.' This Iranian professor explained that water acts like a cushion between rock and soil elements, and when it is unusually extracted, solid materials stick together and can cause subsidence, which in some cases, depending on proximity to active fault systems, can trigger minor and major earthquakes. He continued, 'Some rains and flash floods can never compensate for the water output because replenishing the main water is a long process, which is why water cannot infiltrate the ground, and we witness flooding. In other words, the pore spaces collapse due to water extraction, and reopening them requires significant energy and time.' In response to the question of what solutions exist for a country like Iran, he said that most of the available water in Iran is used in agriculture, which is something that needs more focus, and this issue can be addressed through advanced agricultural systems. Tahmasbi added, 'I believe possible solutions include not extensively extracting water and also making irrigation systems more advanced and efficient, as well as avoiding planting some water-dependent crops like rice and alfalfa in areas where there is water scarcity and subsidence risk.' Researchers at the Colorado School of Mines have shown that 6.3 million square kilometers of the Earth's surface (about 5 percent of the total land area) are prone to subsidence levels that may cause damage and require attention, as they affect about 2 billion people (25 percent of the world's population). There have been multiple warnings about the critical state of land subsidence in Iran, but no action has been taken in this regard. For instance, Mehdi Zareh, a faculty member at the International Institute of Seismology and Earthquake Engineering in Iran, recently told the Rokna news agency that seven provinces and 200 cities in Iran are in a 'critical state.' Ali Bitahli, head of the risk assessment department at the Road and Urban Development Research Center, also described the subsidence rates in Iran as 'staggering' and stated that Iran has the second-highest subsidence rate after India. The head of the Iranian Mapping Organization stated in January 2023 that the average subsidence rate in the country is 15 centimeters, which is 'five times the global average.'