In this post we’ll discuss how to worldbuild desert climates, where desert climates can be found across an earth-like planet, as well as looking at some iconic desert flora and fauna on earth, and how to create some of your own.

Hey everyone, my name is Matthew, at least unless I’m a mirage, and this discussion is part of a series where I will be going through a science-adjacent worldbuilding process step-by-step. Last time we discussed the savannas of our fictional world of Locus, looking at how the flora and fauna there have adapted to the harsh conditions of the dry seasons and bushfires.

For today’s discussion, we’re going to be looking at a different but no less harsh climate, the desert. The great expanses of sand dunes and stony steppes that might look like there’s not much on the surface but are veritable ecosystems in their own right.

Deserts, according to the Koppen Climate Classification system, are categorised as areas that experience less than a certain threshold of rain per year. Areas that experience less than 50% of the precipitation threshold are considered ‘arid’, while areas that experience between 50-99% of the precipitation threshold are considered ‘semi-arid’, forming a transitionary climate zone called a Steppe, which are found between deserts and their surrounding climates.

Deserts are then further separated into hot and cold deserts, which are simply categorised as ‘hot deserts’ having all months with average temperatures above 0 degrees Celsius, while ‘cold deserts’ have at least one month where average temperatures drop below 0. In addition, a third desert classification exists for deserts along areas affected by cold ocean currents, which are called foggy deserts. Despite being some of the driest areas on the planet in terms of precipitation, they experience frequent fog that rolls in from the coast. These foggy conditions can also exist similarly in steppe climates.  

Before we discuss where to place deserts on the map, we first need to understand rain shadows. A rain shadow is the geographical area on one side of a mountain range that is blocked from receiving rain by the mountains. As wind blows onshore from the ocean it brings with it moisture, which is distributed across the land usually in the form of rain. When this wind-carried moisture encounters a mountain, it deposits most if not all of its moisture on the side of the mountain it approaches from. By the time the wind has lifted over the mountain, it has lost its moisture to precipitation on the shoreward side of the mountain, and so continues onward as dry wind. This process is called Orographic Lift. What this means in real terms is that the geographical side of a mountain range that is blocked from offshore winds will receive minimal if any rain, and therefore is within a rain shadow. On earth, most of our well-known cold deserts are within the rain shadows of mountain ranges, such as the Atacama, the Gobi and the Great Basin. Hot deserts can also form in more equatorial areas if the area is affected by a mountain’s rain shadow.

This is the map of Locus, which is the earth-like world we’re creating across this series. As you can see, we’ve already placed the tropical climate zones on the map. On planets with similar temperatures to earth, hot deserts are going to be between 10 and 30 degrees north and south, extending more towards the poles in areas affected by cold currents and directly onshore from prevailing winds. Cold deserts on planets with similar temperatures to earth can fit anywhere between 30 and 75 degrees north and south, but only occur in places that are extremely dry, usually the most interior parts of continents, or areas that are within a mountain’s rain shadow.

But what if your planet is hotter or colder than earth? Well, hot deserts won’t necessarily expand just because the temperature rises on a planet. Instead, what causes deserts to expand is lack of precipitation. If an earth-like planet is warmer than earth, hot deserts will eat into some of the temperate areas, though cold deserts will stay in roughly the same locations. If your planet is colder than earth, like Locus is, then we can see that savannas extend further from the equator, reaching as far poleward as 25 degrees in areas affected by warm currents. What this means is that hot deserts only stretch down towards the equator in continental interiors, and in areas affected by a rain shadow. Cooler planets like Locus will have deserts stretch poleward towards 35 degrees in continental interiors, areas affected with cold currents, and shores affected by prevailing winds. Cold deserts, once again, still form between 30 and 75 degrees within the same locations. Which gives us a desert coverage of something like… this. On a cooler planet like this, deserts are likely to only be considered ‘hot deserts’ if they are closer to the equator than 25 degrees north and south, while any desert further poleward than that is likely to be a cold desert. Uniquely, this means that a single desert like THESE can be both hot and cold in different areas.

Regardless of being hot or cold, deserts are exceptionally dry, with many going years if not decades with no rain at all. Temperatures in both kinds of desert can reach higher than 50 degrees Celsius, with the record on earth being 56.7 degrees Celsius, in Death Valley, California. The highest outdoor temperature I’ve ever personally experienced was 46.4 degrees Celsius, and that was more than hot enough. Even cold deserts can reach maximum temperatures of similar heights, though in winter, cold deserts can become painfully cold at night, with the Gobi Desert’s recorded minimum temperature being negative 38 degrees Celsius. This severe temperature disparity between hot and cold often makes cold deserts even more inhospitable than hot deserts, making them some of the most truly barren places on the planet.

Of course, as a particular movie once quoted, life finds a way. Flora in deserts face a severe challenge, as they require the sun for photosynthesis, but also direct sun exposure in a desert can cause rapid overheating. Most desert-dwelling plants will have adapted to this by abandoning their photosynthetic leaves altogether, with their remnant chlorophyll displaced into their trunks. They also need to prevent water loss through evaporation, and so plants grow to shapes that maximise volume while minimising surface area. Finally, as sources of water themselves in otherwise barren environments, plants need to protect themselves, and on earth there are many successful adaptations that desert flora have utilised to do so. Of course, the most iconic defence mechanisms desert plants on earth use are spikes or thorns, with the most well-known desert plants in general being cacti, yucca, and tumbleweeds, though tumbleweed doesn’t refer to an actual group of organisms, but rather is what we call the unique method of seed dispersal that many species of desert plants use. As you can see, there are some clear trends among desert flora when it comes to their characteristics and how they look, so any desert flora we worldbuild for our own projects are likely to be similar.

On Locus, the most successful desert florae are the Pilospina, with extremely similar adaptations to many cacti on earth. One of the more interesting types of Pilospina are the Salrubus, which have evolved to become halophytes, meaning that they have exceptional tolerance to salination, or salty environments. A variety of halophytes exist on earth, such as salt marsh grass and saltworts. Salrubus exist across the salt pans found in deserts, and use a fictional process called severance to consume energy from its environment, specifically utilising thermo-severance, which drastically reduces the temperature of the nearby area. Here’s a link to the video explaining how this process works. If this sounds familiar though, it’s because the Miraculum trees within the savannas of Locus have the same trait. The two groups of flora have convergently evolved to access thermo-severance, though while Miraculum evolved it to protect itself from wildfires, Salrubus requires it for water. The arid air of the desert contains exceptionally minimal water, and when water does arrive it evaporates rapidly due to the extreme heat. Through thermo-severance, Salrubus keeps the water cool and significantly reduces evaporation, allowing small pockets of water to accumulate around it. The salty environment Salrubus lives in reduces the freezing point of water, allowing liquid water to be present underneath an icy surface. Through this method, Salrubus can survive for years without additional rainfall, though can’t survive longer than a few weeks if its water source is taken from it and is at risk if a creature consumes its water. This is in part why Salrubus only exist in areas of high salt content because the water it lives off is far too salty to be safely drinkable by most creatures. Despite this, Salrubus is a particularly uncommon plant and regularly dwindles down to dangerously low numbers.

The other folia species we’ll worldbuild for the deserts of Locus are the Ultimus, in reference to it truly being the final organism that can survive within the absolute most extreme environments of the desert. It is considered an Oligotroph, which means that it requires extremely low levels of nutrients to survive and has an incredibly low metabolic rate. It is still photosynthetic, using the sun to power its bodily functions, but also utilises a fictional process called electrosynthesis, which allows it to create its own electrical energy.  This electrical energy is projected outwards, and Ultimus is almost constantly emitting arcs of electricity that are quickly grounded by the environment. Where the magic really happens however is within the inhalation sac that Ultimus uses to trap oxygen and nitrogen. Once these gases from the air are trapped, Ultimus uses electrosynthesis to increase the electrical charge of the atoms themselves, transmuting them into other elements. For an in-depth explanation of how this works, there’s a link to the video on this process in the corner, but functionally this means that Ultimus is creating unstable isotopes of elements which, through the process of radioactive decay, emit single protons which become hydrogen. This hydrogen then bonds with the oxygen trapped in the enclosed environment to create, you guessed it, water. Ultimus is literally creating its own water, atom by atom, and though the quantities created are borderline insignificant for most other organisms, it can live off these tiny quantities for up to a century. For future alchemists and scientists on Locus, Ultimus is likely to be a key factor for harnessing the power of transmutation, assuming they can manage the electrical and radioactive dangers that the organism presents.

We’ve talked lots about desert flora, but there are definitely fauna that make the deserts their home too, though their numbers are not extensive, especially within cold deserts. Some iconic desert dwellers on earth include camels, dingoes, fennec foxes, sand cats, scorpions, and snakes. Many desert creatures have adaptations designed to regulate body temperature, such as large ears for dissipating body heat, fur or skin with lighter colouration to reflect heat, hairy paws or feet to provide heat protection when walking on hot sand, the ability to store water in some capacity like camels’ do within their humps, and perhaps most commonly, being nocturnal and living within a burrow. The desert environments are harsh, and it is extremely likely that any fictional desert dweller will have similar adaptations to these in order to survive.

On Locus, the Rolli are rotund creatures whose bodies are comprised of a thick layer of fat surrounding a water sac called a bladder. They are relatively small creatures, and when parched resemble a shrew-like animal, though when they come across water, they will drink until their bladder is full, and swell to their iconic ball-like shape. In this way, Rolli are able to store more than their entire body weight in water, which can last several months. Once swollen however, they can no longer effectively use their legs for locomotion, instead rolling across the dunes in groups that are called a ‘drift’, which leads to some truly comical sights as these cute balls make their way across the desert, led by a matriarch who has memorised safe passages across the dunes. Given their unique method of movement, paths tend to be as downhill as possible, and getting stuck within a dune valley can be very dangerous for Rolli, separating them from the drift and leaving them exposed to predators as they slowly waddle their way back to the path. They present attractive targets to predators, not just for food but also for hydration, though Rolli moving at full speed downhill are often too fast for many predators, meaning their best chance to survive their trips through the desert unharmed is to keep moving downhill as much as possible. Their paths are easily noticed, and many other creatures use them as markers for both easy navigation and for directions to water.  

Among desert carnivores, a common feature found across the board is high success rates while hunting. Hunting costs energy, and predators that expend too much energy aren’t going to survive within the deserts. On earth, this is clearly evident if we look at creatures like cats; the cats that live in arid environments like the sand cat and the black-footed cat have the highest successful kill rates out of any feline species. Which means that technically THIS creature is a more efficient killer than THIS creature. One way that many desert animals increase their kill rates is to use venom. Venom is a type of toxin that creatures utilise in order to incapacitate and even kill those that it is used on. Venom is exceptionally widespread on earth, convergently evolved by a variety of creatures, and is very heavily selected for, meaning that once creatures evolve to use venom, it’s likely that it will become the frontrunner for their means of hunting or survival. While the prevalence of venomous creatures here in Australia has become something of an international meme, the reality is that many creatures here have been heavily pressured to evolve more and more potent venom. The inland taipan for example is the most venomous land animal on earth, which we are able to determine through its Median Lethal Dose, which is more commonly called Lethal Dose 50, or LD50, and is the lethal dose of a toxin that will kill a creature 50% of the time. LD50 is usually measured in milligrams per kilogram, with the lower the dosage required, the more venomous a creature is. The inland taipan has an LD50 of 0.025mg per kilogram, with an average dosage per bite of around 100mg, meaning that on average, 50% of creatures up to 4,000kg will be killed from a single bite.

While on Locus many desert dwellers would use venom to assist with hunting, it is the Respirafinalis that is the most dangerous, inspired by the Grootslang, a creature within African mythology. By Frigidi standards, they are quite small, shifting between pure white in colouration when in warm conditions, to jet black when in cool conditions. When it is hot, they flush their tail membranes with blood, flapping their tails rapidly to cool themselves down, while in cool conditions, they shiver to increase their body temperatures, allowing them to transition from hot to cold climates. In such extreme environments, they cannot afford to let any meal go, and so have evolved to be very aggressive, with two external tusks laced with the most potent venom of any land-dwelling creature on the planet. The LD50 of Respirafinalis venom is 0.02mg per kilogram, and a single coated tusk delivers a dose up to 125mg, though it always strikes with both at once. This means a single strike will kill 50% of creatures weighing up to 12,500kg. Specifically, the concoction of Respirafinalis venom causes the body to go into immediate shock, and the venom rapidly paralyses the diaphragm muscles and lungs, meaning that getting struck by Respirafinalis literally causes a creature to take its final breath.

So, to recap, deserts are categorised as areas with access to minimal or no moisture, with flora and fauna there needing very specific adaptations to survive. Some species use unique methods to create their own water access, while others have adapted water storage to carry water around with them. Predators have also adapted highly effective hunting strategies such as powerful venom, to minimise the energy required for each hunt and to increase the chance of securing a meal.

Join me next time when we look at the temperate zones, starting with the interior Continental climates. And until next time… stay awesome!