Climate change is affecting the lives of many people worldwide. Understanding how natural processes are being altered by the changing climate is crucial to predicting and mitigating its consequences.

Among the natural hazards, landslides are typically described mechanistically through the equations of statics and dynamics, coupled with descriptions of hydraulic flows. Current models can assess changes in slope stability due to earthworks, shaking, and the effects of rainfall, snowmelt, and floowing.

Soils containing clay minerals are the most prone to landsliding because they are intrinsically weak: clay particles have low friction and they swell and disaggregate in contact with water. The role of clays in landsliding is well studied. Moreover, they are very spread across the world and are often involved in disasters.

Now, clays are very sensitive to temperature: most of their properties vary significantly upon changes that naturally occur across the seasons in typical temperate climates. These changes affect the permeability, stiffness, swelling behaviour, and mechnical strength. Notably, these changes are well known to scientists but their effects are complicated to predict. Only recently, with the rise of some advanced models, the awareness and confidence in these predictions are increasing.

Yet, the effects of temperature are not accounted for in commercial or conventional slope stability and landslide simulations, and they are not mentioned in policy recommendations for hazard and risk assessments and action plans.

As a result, especially in the current climate crisis, with weather extremes and rapidly rising temperatures, we may be underestimating the effects on geological hazards that stem from slope instability (landslides, floods, …), with consequences that may range from miscalculated damages to life tolls.

In our recent paper, published in Results in Engineering (open access, available here and here), we performed a laboratory study on the influence of temperature on the shear strength (the key parameter in landslides) on two very different clays. We employed the experimental results in a computer simulation, thanks to which we demonstrated the important effect that changes in temperature can have, across the seasons and in the longer term – under climae change, on the stability of clay-rich slopes. We showed that temperature can affect the factor of safety (a classic measure of safety margin) by 10-20% for potential landslides reaching depths of up to 6 meters, which are the most common, with likely scenarios of climate change adding a further 7%.

Considering that most slopes are deemed stable and do not display important deformations even with small safety margins (few %), the importance of not ignoring the role of temperature under climate change becomes clear. This role adds of course to other better studied effects, such as the increased likelihood of weather extremes, including dry and wet spells.