Hot Deserts as a System
- Deserts can be hot or cold with high levels of aridity
- They are defined as:
Areas that receive less than 250mm of precipitation per annum
- Deserts are described in terms of their deficiencies:
- Water
- Soil
- Vegetation
- Population
- Deserts produce the smallest amounts of organic matter and have the lowest net primary production (NPP)
- Desert environments are natural open systems with inputs, outputs, transfers/flows and stores of sediment, water and energy
Table of Desert System Elements
Inputs | Outputs | Stores | Flows/Transfers |
Sun | Landforms of erosion and deposition | Sand and sand dunes | Wind |
Wind | Loss of water through evaporation, transpiration and rivers | Rivers and lakes | Water |
Water | Loss of sand/sediments by wind | Salt pans/playas | Insolation |
Weathering sediments | A build-up of sand through time | Plants | Weathering |
Human activity | Human activity - desertification | Animals | Mass movement |
- Desert systems are generally in dynamic equilibrium, where the inputs and outputs are balanced, for instance:
- Seasonal winds lead to small, short-term changes in a sand dune's profile
- However, overall the shape of the dune mostly remains the same
- Any changes to an input or output can cause positive or negative feedback loops
- Positive feedback results in the change being enhanced
- Less vegetation reduces evaporation and lowers humidity which reduces precipitation rates leading to less vegetation etc.
- Negative feedback restores balance - it checks any change
- Temperature increase raises evaporation rates and dries the surrounding surface, making it easier to erode
- Dust clouds form, which blocks some insolation, reducing temperatures and slowing evaporation
- Positive feedback results in the change being enhanced
Exam Tip
It is important that you use the systems theory in your answers, including feedback loops and dynamic equilibrium. Open systems are self-regulating. They will adjust themselves to flows of energy and matter by changing the interrelationships of elements in the system, resulting in the inputs and outputs rebalancing to a steady state again (dynamic equilibrium).
The hot desert water cycle showing the depth of water stores and high rates of potential evapotranspiration (PET).
- Rain is low and irregular, interspersed with heavy downpours
- Actual evapotranspiration is low, but the potential is high
- Water from aquifers is capable of reaching the surface naturally or abstracted through wells