Natural soil drying in relation to climate: Impact on food production and stability of buildings

Natural drying is due to complex interactions between a porous body (composed of organic or inorganic materials and substances) and ambient conditions. In the present case, the porous body we analyze is loamy soil available for food production. This type of soil is mainly composed of clay, silt and sand in different proportions, depending on the geographical location and the long historical evolution of the terrain. It also contains organic matter decomposed from the rest of previous crops and nutrients. In order for plants to develop, water is essential and its content could vary significantly with the amount of precipitation, incident solar radiation, temperature and wind.

Soil water stress can produce negative effects, including depleting grain yield, reducing the possibility for plants to extract essential nutrients (nitrogen, phosphorus, potassium and micronutrients), being susceptible to pests and diseases, delaying the stage of growth, extending the time of crop and reducing the quality of the collected grains. Also, changes in water content can affect soil properties such as plasticity, texture, structure, thermal conductivity and heat capacity.^[1]

Despite being a relatively stable soil characteristic, soil texture has a significant impact on soil properties and influences the sensitivity of the soil to different climatic changes. As repetitive wetting and drying of the soil promote crack formation, shrinkage and swelling, clay soils are particularly vulnerable to climate change, especially when the number of wetting and drying cycles increases. Developed cracks under continuous wetting and drying cycles allow direct movement of water from the surface soil to permeable substrate or drains through bypass flow, which decreases the filtering function of the soil, hence increasing the loss of nutrients from soil and pollutes the water bodies. This phenomenon could become intense if longer and more frequent droughts are followed by more intensive precipitation. Climate change may indirectly affect the vegetation pattern and land-use practices as well as soil biological function (due to the sensitivity of soil macrofauna and microorganisms), which in turn affects soil properties as well as soil fertility.

The measurement of soil water content can be made through satellite and ground instruments. In the case of satellite equipment, NASA Soil Moisture Active Passive (SMAP) mission employs radar and radiometer instruments. The mission is designed to obtain a better knowledge of soil moisture, improving at the same time the understanding of important planetary cycles: the cycling of water between the surface and the atmosphere, the cycling of energy from the Sun arriving on Earth (as solar radiation and back up into the atmosphere) and the cycling of carbon among plants, atmosphere and soil. The European Space Agency and the Argentina National Commission on Space Activities obtain similar data from the Sentinel 1 and SAOCOM satellites, respectively.

Ground measurement of soil humidity can be made using different techniques, such as gravimetry, which is simply to select a given fraction of soil near the surface to measure its mass change from the initial situation to the final one after drying the sample; by sending an electromagnetic pulse into the soil and recording the backscattered signal and by measuring the soil electric capacity, which is a function of the quantity of water present in the soil.

In many regions of the world, soil humidity is currently (and will be even more so in the future) significantly affected by changes in the climate. One of the ways to quantify the impact of climate change is by means of the analysis of soil drying, which can be accentuated by the intensity of heat waves due to global warming.^[2] According to the 2023 IPCC assessment report,^[3] global warming has unmistakably been driven by human activities, particularly through greenhouse gas emissions. The Northern Hemisphere has seen the raise in the mean surface temperature by about 0.6 °C in the last century^[4] while the number all over the planet was 1.1 °C up to the end of the 2010 decade (having as a reference the 1850–1900 period) as detailed in the 2023 IPCC report previously mentioned. In all scenarios of temperature increase, the severity of the effect of drought is major in many regions due to the loss of soil moisture.

Furthermore, the anticipated worldwide climate change, which entails elevated temperatures and atmospheric greenhouse gas emissions, mainly carbon dioxide (CO₂), alterations in precipitation patterns and atmospheric nitrogen accumulation, impacts diverse soil physical, chemical and biological characteristics that are crucial for reinstating soil fertility and productivity. By implementing some adaptation and mitigation strategies, such as integrated nutrient management, conservation agriculture and residue management, the adverse impacts of climate change on soil fertility may be minimized.

Another climatic event that can significantly modify the normal situation of a soil and consequently the quantity of grains that can be collected in a crop is the El Niño Southern Oscillation (ENSO). It is a modification of the equatorial Pacific near-surface water temperature, influencing the climate of many regions of the world and affecting the normal situation of the soil. Its negative phase is called La Niña and, in particular, in an extended region of South America (mainly Southeast of Argentina and Central Brazil), a 3-years drought period was present in 2020–2022, reducing largely the soil water content and consequently the crop production, mainly soybean,^[5] putting at risk global food security.

Consequently, efforts need to be made to solve or at least to reduce soil water scarcity, for example, by employing seeds more adapted to drought or reducing the loss in irrigation systems. It can be made by changing to underground tubes for sub-surface irrigation or covering water canals with a shadowing protection to reduce evapotranspiration or even with photovoltaic systems. This novel application of solar electric power plants not only reduces water loss, but also increases electricity production, since the panels are water refrigerated, increasing the quantum efficiency of solar cells.

Another important effect of natural drying of soils is the appearance of fissures in buildings due to soil compression (or density increase), technically known as subsidence.^[6] Since the settlement cannot be uniform, the differential changes in soil density due to drying can produce not only fissures several millimeters wide, but also cracks several centimeters wide. This phenomenon is brought on by changes in the properties of the soil, in addition to sudden fluctuations in moisture, which may trigger structural fissures in terms of differential settlement that frequently result in catastrophic failure. This effect was registered in a city house near the Uruguay River, during the last 2020–2022 (historic record) droughts in Central Argentina. Consequently, it is of importance to know not only the properties of a soil at the moment of building construction, but also during all the (extended in many decades or even centuries) period of its life cycle.

Rubén D. Piacentini
Institute of Physics Rosario, CONICET – National University of Rosario, Rosario, Argentina and Technological Institute of Design and Innovation, Faculty of Exact Sciences, Engineering and Surveying, National University of Rosario, Rosario, Argentina
[email protected]

Adriana Ipiña
Institute of Physics Rosario, CONICET – National University of Rosario, Rosario, Argentina

Aparupa Pani
School of Civil Engineering, KIIT Deemed to be University, Bhubaneswar, Odisha, India

Disclosure statement

No potential conflict of interest was reported by the authors.