Impact of ENSO events and climate change on soil drying

Soil surfaces can experience drying as a result of anthropogenic activities, natural events or a combination of them. Human-induced activities such as agriculture, overgrazing and deforestation can lead to reduced soil moisture as such activities tend to degrade soil quality and increase susceptibility to erosion.^[1,2] Soil natural drying causes gradual reduction of moisture content due to various environmental factors without artificial intervention. One important factor is ENSO (El Niño-Southern Oscillation), a major climatic variability event mainly characterized by the periodic fluctuation of ocean temperature in the central and eastern equatorial Pacific, accompanied by changes in atmospheric circulation patterns. These oscillations can affect global weather patterns, agriculture and world economy, among other effects. Additionally, the complex context of climatic change significantly influences the soil mineralogical and geotechnical characteristics.^[3]

During El Niño events, some regions of the world experience drought conditions, leading to soil drying and associated impacts on agriculture, water resources and ecosystems. Conversely, La Niña events often bring enhanced rainfall to certain regions that alleviate drought conditions and replenish water sources. However, the increased rainfall can also lead to flooding, soil erosion and other related hazards. The effects of El Niño and La Niña can be the opposite as those described above, depending on the analyzed region.

Short-term climate fluctuations yield significant influences over hydrology, with El Niño/Southern Oscillation (ENSO) standing out as the predominant mode of such variability, impacting regions globally. ENSO’s direct effects are particularly severe, mainly in the inter-tropical region, notably affecting monsoon-dependent countries.^[4] Soil moisture, representing water stored in the unsaturated soil zone, serves as a source for atmospheric water through processes like evapotranspiration, including plant transpiration and bare soil evaporation. However, due to intense climate change and ENSO events, a continuous cycle of wetting and drying emerges, profoundly altering soil properties, reducing bearing capacity, increasing soil suction, higher differential settlement and fluctuating groundwater levels. Additionally, within the broader context of El Niño and La Niña impacts, these climatic events often bring in different parts of the earth and different years: (a) increased rainfall, fostering higher groundwater recharge rates and storage levels or (b) reduced rainfall and drier conditions that lead to diminished recharge rates and lower groundwater storage.^[5] Consequently, the inconsistent replenishment and sudden depletion of groundwater can disrupt the groundwater table, affecting the capillary zone or aquifer fluctuation.

Furthermore, frequent or alternating changes in soil moisture content, coupled with fluctuations in the groundwater table, can pose significant risks to the structural stability of residential buildings. These risks include increased potential for sub-soil collapse, consolidation settlement, reduced bearing capacity and the formation of cracks due to the cycle of wetting and drying.^[3] To address these challenges, approaches have been developed to understand soil behavior and engineer structures capable of tolerating the resulting ground movements caused by moisture variations.

Addressing soil drying amidst climate change and ENSO events requires a mix of mitigation and adaptation measures. These include sustainable land management practices like agroforestry, conservation tillage and moisture conservation techniques such as mulching and cover cropping. Additionally, improving water storage infrastructure, utilizing drought-resistant crops and promoting climate-resilient farming methods can help communities adapt to adverse climatic conditions. The adaptation strategies are crucial, not only for maintaining soil health and agricultural productivity, but also for mitigating broader environmental impacts, like those associated with atmospheric aerosol dispersion.

In relation to the atmospheric aerosol (particulate matter) dispersion, wind erosion constitutes one of the primary physical mechanisms through which soil dust particles are transported into the atmosphere.^[1,2] Dust particles are commonly characterized as PM10 (particulate matter equal or smaller than 10 μm). Arid and semi-arid regions are typically dry environments where soil moisture is low, leading to weakened binding forces between these soil particles and the soil surface. These circumstances promote the injection of aerosols into atmosphere, although its permanence is highly dependent on the particle size as well as other meteorological variables such as rain and wind speed.

In contrast with other aerosols, dust particles can not only absorb, but also scatter solar radiation. An increase in atmospheric aerosols loading can have diverse consequences into the atmosphere. For instance, dust aerosols can lead to a reduction in net surface radiative forcing by about 1 W m⁻², a value significant to influence climate change.^[2] This radiative forcing is defined as the net balance in sun and earth radiation at the top of the troposphere, which is placed between about 10 to 14 km of altitude. In contradiction, this decrease in surface radiation is accompanied by increased atmospheric heating. These results point out the complex interaction between soil moisture, aerosol generation and climate dynamics. Furthermore, there are radiative transfer models that indicate that changes in soil moisture can increase the warming effect caused by greenhouse gases.^[6] As the climate warms, soils tend to get drier in many regions. This feedback loop exacerbates the warming trend.^[6] It is noteworthy that approximately half of the atmospheric dust is currently attributed to anthropogenic activities, like the ones described in the work of Tegen et al.^[2] Understanding the implications of these activities can help mitigate the above-mentioned processes; these are indeed crucial for addressing climate change and its associated impacts.

Since the soil drying phenomenon is global in scale, a meaningful impact needs the entire world to take suitable mitigation measures. Human intervention to influence the soil drying/wetting caused by global warming is difficult to be feasible in the short term, but an effort must be done in this direction. If the diverse measures detailed earlier (and others) are implemented on a truly global scale, we can expect a positive impact on food security, structural stability of constructions and air quality.

Rubén D. Piacentini and María Fernanda Valle Seijo
Institute of Physics Rosario, CONICET - National University of Rosario, Rosario, Argentina
[email protected]
Aparupa Pani
KIIT Deemed to be University, Bhubaneswar, Odisha, India

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Notes on contributors

Rubén D Piacentini

Rubén D. Piacentini is a Senior Researcher in Atmospheric Physics, Solar Energy and Climate Change, at the Institute of Physics Rosario, dependent on the National Council of Scientific and Technical Research of Argentina and the National University of Rosario. He is a Honorary Professor of the National University of Rosario in Postgraduate, Master and Doctorate Courses. He is a corresponding member of the National Academy of Exact, Physical and Natural Sciences of Argentina and a founding member, by invitation, of the Academy of Medical Sciences of the Province of Santa Fe, Argentina and Coordinator of its Environment and Health Commission. He is an Expert Reviewer of Reports of the United Nations Intergovernmental Panel on Climate Change (IPCC). He is also Co-author and Reviewer of the World Reports published by the World Meteorological Organization and the United Nations Environment Program, related to the Montreal Treaty that limits the emissions of stratospheric ozone depleting substances.

María Fernanda Valle Seijo

María Fernanda Valle Seijo is a PhD student at Rosario Physics Institute, dependent on the National Council of Scientific and Technical Research of Argentina and the National University of Rosario and an Assistant Professor in the Geographic Information Systems course of the Faculty of Chemistry and Engineering, Catholic University of Argentina. He obtained an undergraduate degree in Environmental Engineering, Faculty of Chemistry and Engineering, Catholic University of Argentina and a postgraduate degree as University Senior Professor, Faculty of Law, Catholic University of Argentina.

Aparupa Pani

Aparupa Pani is an Associate Professor, School of Civil Engineering, KIIT University, Bhubaneswar, Odisha, India. She obtained prestigious SERB Core Research Grant GOI (as a PI). She is Faculty Coordinator for the MoU between Odisha State Pollution Control Board and KIIT University, facilitating academia-industry research programs in collaboration with the Odisha state government; a Faculty In-Charge, Research & Development, School of Civil Engineering, KIIT University; and Faculty In Charge Team Kamakshi (HeforShe) Women Empowerment, KIIT University.