2. Summary: Dryland Strategies
Arid zones have much greater annual evaporation rate than rainfall, the rains come in
just a few quick large intense events usually in mid winter. Soils usually contain plenty of
nutrients but need humus and water to be released.
The concentration must be on increasing soil life cycles with plants cycles that decrease
evaporation through shade, wind buffering and mulch additions which in turn increases
the efficiency of the water cycles as all these are crucial for establishment in an arid
environment.
Desert strategies primarily are all about reducing evaporation, which means they are
water-connected. Great attention and detail must be paid to wastewater in mulched
home gardens, flood flow during the few large yearly events and runoff from all hard
surfaces natural or manmade.
Deep rooted pioneer trees need mulch and drip irrigation in establishment for shading,
wind buffering leading to mulch production when established that can be can and
added to for crops and fruit trees. At the first rains of winter most tree mulch is cut
allowing plenty of time for re-growth for summer shaded.
3. Summary: Dryland Strategies (cont.)
Summer is the slow period of the year where often heat and water stress are extreme.
Fertilizer additions are mainly made during the winter months in milder time of year.
The major arid zone deserts of Earth are in the sub-tropics at the extreme end of the path
of the vertical sun, the Tropic of Capricorn at latitude 23 south and Tropic of Cancer at
latitude 23 north. There are cold and hot arid zone occurring at high altitudes through to
lowest landscapes on Earth at 400 meters below sea level.
Problems of aridity, salted soils, and long-term drought can always be expected where we
venture into desert borders with pastoralism and cropping, for added to the natural
background fluctuations of rainfall due to earth and moon orbits, and solar radiation
variance, we as exploiters add deforestation, soil erosion, and the consequent salting of
waters and soils. All desert areas are extending; many dryland areas are being created,
and antecedent plant and animal species are thereby brought to extinction.
A great many arid-area species are not so much dry-adapted as drought-evading. Plants
dry off, cease growth, or exist only as seeds and tubers in drought. Many trees are drydeciduous, evading the worst effects of drought in a leafless state, but truly droughtadapted plant species also exist, and use wax, insulation, reduced transpiration, and large
water storage organs to withstand drought.
4. Summary: Dryland Strategies (cont.)
Increasing desertification of agricultural lands has focused world attention on salt and
drought-tolerant plant species of potential use. The semi-arid and transitional areas are
particularly species-rich, thus desertification is taking a rapid toll on potential useful plant
diversity.
Arid zones are areas where direct evaporation exceeds rainfall, and where annual
precipitation averages fall below 80 cm, and as low as 1 cm (sometimes only as dew).
Although the greater part of these areas are hot desert, there are substantial montane
hot-cold deserts, and very cold desert areas near the north and south polar regions.
Typically, an extensive hot desert area consists of a savannah edge towards more humid
monsoon areas, a Mediterranean climate edge, extensive scattered shrub–forb
associations (forbs are any non-grass or herbaceous plants) dunes on harder pavement
areas, and almost bare pavements of harder rocks with faceted pebbles.
5. Some features of the deserts are:
• Plants produce copious seed with long viability: seed is often wind dispersed.
• Termites and ants are often more effective than worms as soil aerators and
decomposers.
• Rain may fall in mosaic patterns, so that vegetation is also a varied mosaic of fire and
rain, and ephemeral plants at different response stages from growth to decay are evident.
New generations of shrubs may experience favourable seeding conditions as rarely as
every 7 – 20 years. This then becomes the period of recruitment of new forests or
shrublands.
• Much of the water run-off system may end not in rivers but in inland salt-pans or basins
(endorheic drainage), from which all water eventually evaporates.
• Normal erosion is by wind but rare cloudbursts shape the main erosion features and
move vast quantities of loose material from hills in turbulent stream flow. Wind
transports materials locally in dust storms.
6. Some features of the deserts are (cont.):
• Animals burrow, seek shade, or are nocturnal in order to conserve water; many are
highly adapted for water conservation.
• Plant associations may be [highly] varied in response to changes in long-term aspects
such as slope, soil depth, salinity, browsing density (in reference to livestock), pH, and rock
type.
SEMI-ARID areas have steppe, scrub, and low forest vegetation, ARID is steppe and
scattered low shrubs, and true DESERT has little but oases and ephemeral vegetation
appearing after the rare rains. Deserts have a rainfall classification of:
• Hyperarid: 0 – 2 cm annual average (e.g. Atacama, Namib desert, central Sahara).
• Extremely dry: 2 – 5 cm annual average.
• Arid: 5 – 15 cm annual average (e.g. Mohave, Sonora, Sahara margins).
• Semi – arid: 15 – 20 cm, maximum 40 cm (much of the Australian deserts, Asian deserts,
Kalahari).
Above 40 cm, and to 75 or 100 cm rainfall we have (potentially) dry savannah forests;
7. Some features of the deserts are (cont.):
Rainfall is not dependable in arid areas, with a normal 30 % variation, and a potential 90%
variation in any one year. Potential evaporation can range from values of 700 cm/year in
hyperarid areas to 100 cm in steppe.
A paradox in almost all large desert or arid areas is the existence of two types of more
humid environments: EXOTIC RIVERS which flow in from better-watered or forested
regions, and OASES. There is a third, invisible water resource, that of AQUIFERS
(underground waters). All must be used with great caution, as water in all of these
resources can be locally exhausted, and aquifers can be depleted over vast areas by
immodest use (as they have been in the USA). This misuse can cause widespread
subsidence, collapse of the aquifer, and a permanent disappearance of those oases which
were in depressions fed by the aquifer.
Instead of concentrating on exotic water in deserts, we should attempt to increase the
input of water into the aquifers, soils, and streams; and to rehumidify the desert air by
planting trees and protecting existing vegetation. It is the presence of trees and shrubs,
transpiring rather than evaporating water, that keep the desert salts from evaporating at
soil level. Once evaporation alone operates, capillary action quickly bring subsurface salts
to the surface as magnesium, sodium, calcium, and potassium compounds (chlorides,
sulphates, carbonates) and we can no longer establish vegetative cover.
8. Designer’s Checklist: Broad Strategies
• Common operations for freshwater infiltration at the top of
catchments, and work downstream as plants establish.
•Give upwind areas the first attention for soil pitting and
windbreak trees.
•Establish plant nucleii or oases at favoured sites and follow out
on corridor planting.
•Spread pelleted seed (e.g. Seed balls) over larger areas to
await a favourable season.
9. Designer’s Checklist: Garden & Food Supply
• Establish shaded and mulched gardens within settlement.
• Establish settlement windbreak and shade trees.
• Extend successful species along corridors of sandy river beds,
wadis, water runnels, foothills. Seek out favoured niches in
rocks, seepages, shaded areas for high value trees and vines.
• Establish water-harvesting swales and fields for wet-season
storable crop. Swales may support trees and vines after a few
rains have infiltrated into the soil.
10. Designer’s Checklist: Water Supply
• Primary drinking water can be supplied by tanks off roof
areas.
• Gardens and firewood plantations are established using a
combination of swales and drip irrigation.
• Broadscale crop needs both windbreak and water harvest at a
ratio of 20 ha of run-off to 1 ha sown.
• Seek out safe dam sites near settlement, in shaded valleys or
off streams diverted to drop silt.
• Store water in sand-filled dams or gabion-stabilized terraces.
•Wherever water is infiltrated into the ground, plant trees to
keep salt levels down.
11. Designer’s Checklist: Water Supply (cont.)
• Never use deep bores or pumped well water beyond the
ability of the recharge areas to re-supply usage. Test all such
water rigorously for salts, radioactives, nitrates, fluorine, and
biological contamination.
Regarding water catchment, our aims can be summarised as
follows:
• To store fresh water for cooking and drinking;
• To divert sheetflow and waste water to gardens;
• To infiltrate water into soils, and top produce plant growth on
that site; and
• To give rainwater run-off time to soak into the landscape
where we live.
12. Designer’s Checklist: Water Supply (cont.)
We can assist aquifer intake by:
• Planting trees on ridges and slopes;
• Building deep interceptor drains on contour near ridge tops
and on plateaus;
• Ripping rock pavement or capstone areas to allow water
penetration;
• Leading surface drains to wells cut n shattered rock; and
• Creating banks of loose surface boulder, or open pits and
swales in gravels.
• Trees, in the long term, keep such systems open to infiltration
and reduce or eliminate dust from loess and sand deposits
from surrounding areas.
13. Biosocial Strategies to Improve Degraded Areas
• Government aid is available as resolving loans, to plant new
crops and to buy in alternative livestock (replacing erosive
species).
NOTE: Medium-to-Long term investment should be encouraged
to gather deploy the resources needed to implement these
plans.
• Community involvement is assured by the employment and
education on unemployed (or underemployed) people
toward projects that relieve their poverty (through
meaningful local work).
• Education is integrated with development.
14. Biosocial Strategies to Improve Degraded Areas (cont.)
• Export crop is being replaced with local nutritional food crop
and tree crop.
• Pioneer legumes have helped improve soil and halt erosion,
while providing forage and food locally.
15. The Desert House
Desert housing needs the twin qualities of summer cooling and
winter (or night) warmth. Some features are:
• Cool courtyards in building interiors; narrow and tall to
preserve shade.
• Evaporation strategies from water in tunnels, unglazed pots,
tanks, fountains, bark mulch, and coke or hessian “wicks” for
water evaporation.
• Narrow east-west streets maximized; broad north-south
streets minimised.
• Use of white-painted massive walls (often of mud) as cool
surfaces.
• Small windows or stone grilles; most light is indirect from the
inner courtyards.
16. The Desert House (cont.)
• Towers, vanes, and airscoops for ventilation systems.
• Cooking outdoors under shade trellis.
• Earth sheltered or underground housing of various types.
• Vines on walls, over roofs areas, gardens, storehouses.
• Roof area creatively used for drying crops, washing clothes,
pigeon lofts, etc.
17. The Desert House (cont.)
Houses can be constructed so that they assist other houses:
• Dense housing, closely placed side by side along an east-west
alignment. Few, if any, north-south cross streets are aligned
to hot winds. Narrow streets, preferably shaded over by
trees or two- to three- story buildings.
• Multiple stories/floors are appropriate in restricted sites such
as wadi banks, niches at the base of cliffs, and small valley
sites. Single story housing is appropriate on more open sites,
but then it needs dense vegetation or trellis on the shade
side.
18. The Essentials of the Desert House
• No west windows; west wall painted white and fully shaded,
vine screened, evergreen trees to the west.
• Cold air tunnel or cold air source as a fully enclosed, barkmulched shade house.
• Positive hot air exhaust as a solar chimney or small attached
glasshouse to the sun side.
• Unimpeded through-ventilation for cool air.
• Either very thick, white, fully-shaded walls (cool deserts and
cool nights) or very light, screened, or matted walls (hot days
and nights).
19. The Essentials of the Desert House (cont).
• Evaporative cooling surfaces in a through-draught (draft); as
unglazed pottery, coke mounds, ferns in bark, think vines, or
wet hessian (burlap) screens.
• Cool cellars for storages, or deep cool internal courtyards
with vines and ferns.
• Ceilings insulated; thick vine mass over roof area.
