What Causes Droughts And Why Do They Stop?

Every business in the world relies on a high quality, plentiful water supply to function, if for no other reason than every human being relies on water to live and function effectively in work and wider society.

This is what makes the potential for droughts such a disruptive element for business, as well as being a humanitarian crisis and ecological disaster in the short term. In the long term, those three consequences intersect and magnify each other.

However, whilst it is self-evident that a drought is a terrible event and typically symptomatic of wider issues in a local area, there are still many questions about what causes droughts, their global and regional effects, what makes their effects intensify, and indeed what stops them.

All of these questions were the impetus for the Dry-2-Dry project funded by the European Research Council, which uses several advanced technologies and updated methodologies to truly explore why droughts happen, and whether they create feedback loops that cause them to get worse.

The Wildfire Effect

One of the dangers of climate change and the many environmental symptoms of it such as droughts is not only the devastation caused by the initial event but its contribution to a feedback loop that makes it significantly worse, more impactful and more difficult to prevent.

Exactly how this takes place is difficult, given that droughts are not always caused by environmental factors but can be caused by a strain on nearby water supplies, disruption to supply chains or a disproportionately severe demand for water.

Many of these factors either intensify or intersect with environmental factors. Heatwaves increase the demand for water in the nearby area, which leads to an increased risk of water scarcity and drought conditions. Human behaviour combines with climate conditions to make droughts more dangerous.

This also can increase the potential for droughts to spread and propagate more widely, as droughts reduce evaporation, which reduces the supply of rain downwind of a drought-affected area. This is how droughts can widen and spread in a particular area.

As well as this, much like a wildfire, the ecological effects of baking the ground, such as a lack of agriculture and a reduction in the ground’s ability to absorb water that can be evaporated later means that even when precipitation does arrive, it may not necessarily solve water scarcity issues.

In fact, drought conditions can contribute to flash flooding, which can cause further devastation and damage to water infrastructure as the baked soil struggles to absorb water.

Once the flood waters leave, there is still potentially a reduction of the water in the land, at least relative to the rainfall levels, which causes further self-propagation. After all, the water supply on a global scale is relatively stable but is disproportionately located.

The effects of flooding were outside of the scope of Dry-2-Dry, which focused primarily on dry, landlocked areas where rainwater supply is primarily provided by evaporation from other remote areas.

The Teleconnected Feedback Loop

The Dry-2-Dry project believed that droughts tend to create feedback loops that lead to other droughts, and intended to prove it through four key objectives, which coincide with the four steps of the feedback loop.

The first step is quantifying and finding evidence that a drought affects the levels of evaporation from plants, trees and other vegetation, as well as directly from the soil.

The effects of a drought on vegetation are largely self-evident, although the project aimed to quantify and fully explain the process.

The hypothesis, later supported through analysis undertaken by Dry-2-Dry, was that when the soil starts to bake, signifying a soil drought, it causes a reduction in levels of evaporation.

This contributes to the warming and lack of humidity of the air in the local area, compounding the heatwave conditions that have caused the drought in the first place, creating a feedback loop that only ends when wind conditions bring rainfall to the area and thus ends the drought.

Quantifying this intensification, and the overall effect on “land feedbacks” (the response of the land to the heatwave and drought conditions), is the second step of the feedback loop.

The third step, and the cornerstone of Dry-2-Dry’s hypothesis, is that droughts do not only serve to intensify themselves in the surrounding area but this same process can also cause drought conditions to spread to other areas, self-propagating and intensifying regional water stress.

This is the wildfire effect described above, and where a large part of the research was targeted.

The lower levels of evaporated water do not affect merely the drought-affected region, but other places downwind of it reliant on those regions for rain. This is how drought conditions can compound, and why droughts and heatwaves are increasingly being found in less arid regions.

The final step was looking at how droughts affect the use of land in the local area, both in terms of the long-term impacts of droughts on agriculture and preventing further damage from extreme weather phenomena, but also in how land use can be used to help prevent droughts and damaging flash flooding.

The effects of the study are partly to explore why droughts propagate the way they do, but also to help tweak and devise effective models that can forecast when and how extreme weather events will hit certain regions.

Much like how a greater understanding of biomarkers can help doctors diagnose diseases at earlier stages where they can be far more easily managed, learning about potential warning signs of heat stress, water scarcity and droughts can help organisations and locals prepare for the impact.

If a business has fair warning that a drought is upcoming, it can work to ensure they are water secure and has a supply of water that it needs to ensure its business continues to function and that its employees are well-hydrated without the great expense that comes from immediate-term reactive solutions.

The next stage of the research is to explore what types of land management strategies and land cover can be used to minimise the effects of heat stress and attempt to break the feedback loops and cycles that can be so devastating.