A number of students struggle with the notion of micro-climates. How can there be different climates when the weather bureau declares my region to be in a particular climate? This is not imagined. The grass can be greener on the other side of the hill. Especially if you are in a dry region and the other side is protected from wind, has more shade and more water.
Figure 3: reflected light and thermal mass from rocky headland which also diverts
cold southerly wind.
These natural factors combine to enhance the microclimate of historic aboriginal fish farming bay [now called boneyard beach], Kiama NSW
What is a Micro-climate?
A micro-climate is a space within a climate that creates a slightly different temperature range due to wind chill, thermal mass, shade or reflected exposure and humidity. We can create a range of micro-climates to nurture a wider variety of food plants in a permaculture property. Frost hollows can support plants that require a chill to set fruit (ie. Cherries), sun-traps can nurture more tropical species. Sunny and dry areas help Mediterranean herbs and fruits to thrive. Some plants such as grape vines and citrus trees enjoy added thermal mass from rocks positioned underneath. Bamboo can be positioned to temper cold winds and their leaves allowed to blow as mulch to area downwind.
1. Topography (aspect and slope)
2. Soil type (cover, colour, texture and smell). Is the soil hard or springy underfoot?
3. Vegetation (bare, grass, shrubs or Tree density)
4. Water (run-off, pooling, patches of erosion, boggy patches)
5. Structures and rocky outcrops (windbreaks, wind tunnels, colour to reflect or absorb light, increased heat or pockets of cold)
6. Slopes that are steeper than 180 because these steep slopes can be vulnerable to erosion and should be protected for stability.
7. Nearby ridges with the potential to direct warm winds or trap condensation.
Key features of different micro-climates and how they are formed
Microclimate features include sun-traps, condensation traps, ponds or dams for reflective light and localized humidity, thermal mass, shade, frost and wind shadows and diversion channels.
Sun-traps aim to hold warm air on site. They often use windbreaks to block harsh winds. The plantings are open to the sun. In subtropical and temperate climates the sun-trap works best when it embraces the mid-morning sun rather than hot afternoon sun. If the sun-trap is positioned on a slope that has a mid-morning aspect, it will have optimum sun exposure. But remember, that most plants in Australia are suffering in summer from over exposure, so design the space to give young plants protection in the hot summer afternoon. You can also include sacrificial nurse species in the early stages of implementation.
Sun-traps on a slope need have water systems that may have a different shape to the garden beds. The garden beds will embrace the sunlight well if they are horseshoe shaped and open to the sunlight but the water system will not want to be the same shape. The water harvest system will need to gently guiding water down the slope.
Don’t be put off by this complexity. Design first an efficient water harvesting shape, then simply plant the vegetation in the required shape over the top. The greatest challenge comes when you need to install roads and paths. But paths can traverse over mounds and diversion drains with grills.
How to design a Micro-climate
1. Gather climate and existing micro-climate your data of the site
2. Determine what you wish to grow there
3. Analyse the required plants needs, functions and intrinsic characteristics
4. Design best water harvest system
5. Position access ways to reinforce the water harvest system and provide solar access
6. Address the points where the water flow and pathways cross
7. Position plants and other man-made structures in the design according to their light, water and shelter needs
8. Include nurse species and other strategies in the staging plan to assist establishment of mature species
Design for micro-climates is a key part of Natural Systems Design (using your analysis theory), Cultivated Ecology (using your understanding of elements and what suits the site) and incorporates Water and soil theory. Utlimately It forms part of your Final Design.