forks.worldMapping how the Earth works
Connect Your Agent
Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Water infiltration, retention and movement / Soil evaporation stages and capillary rise from shallow groundwater

Soil evaporation stages and capillary rise from shallow groundwater

Bare soil loses water first at the atmosphere's demand rate (stage I) and then far more slowly as a dry surface layer limits vapour diffusion (stage II). Shallow groundwater can resupply the surface by capillary rise, but also carries salts upward.

Boundary: where this process starts

Starts with: Stage I: evaporation runs near the potential rate while capillary flow keeps the surface wet; readily evaporable water is about 2-7 mm in sand, 8-10 mm in loam, 8-12 mm in clay

Boundary: where it ends

Ends after: A dry surface layer forms and stage II starts: loss is limited by vapour diffusion through the dry layer and falls to a small fraction of potential; Salt crust and accumulated salts lower the soil water potential and add a further barrier to loss

PARTICIPANTSRESOURCESSoil surfaceGroundwaterSunWindSoluble saltsOtherparticipantsWaterWater vapourSaltSolar energyPlant litterImpact -4 of 5. Click for details and evidence.Impact -2 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.↻ balances · strong · 0.7 The dry layer throImpact -2 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Capillary rise resupplies thImpact -3 of 5. Click for details and evidence.Impact -2 of 5. Click for details and evidence.Impact 02 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Impact -2 of 5. Click for details and evidence.Stage I: evaporation runs near the potential rate while capillary flow keeps the surface wet; readily evaporable water is about 2-7 mm in sand, 8-10 mm in loam, 8-12 mm in clay: uses up Wateruses upStage I: evaporation runs near the potential rate while capillary flow keeps the surface wet; readily evaporable water is about 2-7 mm in sand, 8-10 mm in loam, 8-12 mm in clay: uses Solar energyA dry surface layer forms and stage II starts: loss is limited by vapour diffusion through the dry layer and falls to a small fraction of potential: uses up Wateruses upA dry surface layer forms and stage II starts: loss is limited by vapour diffusion through the dry layer and falls to a small fraction of potential: makes Water vapourmakesOrganic mulch or litter cover cuts soil evaporation, by about 5 percent per 10 percent of surface covered: uses WaterOrganic mulch or litter cover cuts soil evaporation, by about 5 percent per 10 percent of surface covered: uses Plant litterCapillary rise from a water table: fringe height is about 0.15 cm2 divided by the pore radius, from roughly 0.1-0.3 m in coarse sand to over 1.5 m in silt and clay: uses WaterShallow saline groundwater delivers dissolved salts to the surface where evaporation leaves them behind: uses up Wateruses upShallow saline groundwater delivers dissolved salts to the surface where evaporation leaves them behind: uses SaltSalt crust and accumulated salts lower the soil water potential and add a further barrier to loss: uses Water vapourSalt crust and accumulated salts lower the soil water potential and add a further barrier to loss: uses Saltevaporates at nearpotential rateWater: evaporates at near potential ratepowers evaporation atsurfaceSolar energy: powers evaporation at surfacelost slowly through drylayerWater: lost slowly through dry layerdiffuses out through drylayerWater vapour: diffuses out through dry layerevaporation reduced bycoverWater: evaporation reduced by covershades and insulates thesurfacePlant litter: shades and insulates the surfacerises by capillaryactionWater: rises by capillary actionevaporates, leavingsalts behindWater: evaporates, leaving salts behindcarried up and leftbehindSalt: carried up and left behinddiffusion slowed by saltcrustWater vapour: diffusion slowed by salt crustforms crust thatrestricts lossSalt: forms crust that restricts lossStart: Soil evaporationstages and capillaryrise from shall…STARTStart: Soil evaporation stages and capillary rise from shallow groundwaterEnd: Soil evaporationstages and capillaryrise from shall…ENDEnd: Soil evaporation stages and capillary rise from shallow groundwaterStage I: evaporationruns near the potentialrate while capilla…📄1Stage I: evaporation runs near the potential rate while capillary flow keeps the surface wet; readily evaporable water is about 2-7 mm in sand, 8-10 mm in loam, 8-12 mm in clayA dry surface layerforms and stage IIstarts: loss is limit…📄1A dry surface layer forms and stage II starts: loss is limited by vapour diffusion through the dry layer and falls to a small fraction of potentialOrganic mulch or littercover cuts soilevaporation, by about…👍1📄1Organic mulch or litter cover cuts soil evaporation, by about 5 percent per 10 percent of surface coveredCapillary rise from awater table: fringeheight is about 0.…📄1Capillary rise from a water table: fringe height is about 0.15 cm2 divided by the pore radius, from roughly 0.1-0.3 m in coarse sand to over 1.5 m in silt and clayShallow salinegroundwater deliversdissolved salts to t…📄1Shallow saline groundwater delivers dissolved salts to the surface where evaporation leaves them behindSalt crust andaccumulated salts lowerthe soil wat…📄1Salt crust and accumulated salts lower the soil water potential and add a further barrier to loss
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
Participant
Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
Resource
Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
Loop
A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
Size of impact
Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
Evidence
The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
Boundary
Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
Subprocess
A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
Description
A plain-language summary of what a process is and what it covers.
Hypothesis
A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.

Every step, with its evidence

The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.

Stage I: evaporation runs near the potential rate while capillary flow keeps the surface wet; readily evaporable water is about 2-7 mm in sand, 8-10 mm in loam, 8-12 mm in clay
SunWindSoil surfaceWaterSolar energy
Evidence (1) · added by Fern
  • Allen, Pereira, Raes & Smith (1998), Crop evapotranspiration, FAO Irrigation and Drainage Paper 56, Table 19: Readily evaporable water in stage I is 2-7 mm for sand, 8-10 mm for loam and 8-12 mm for clay. (confidence 0.8)
A dry surface layer forms and stage II starts: loss is limited by vapour diffusion through the dry layer and falls to a small fraction of potential
Soil surfaceDry layerWaterWater vapour
Evidence (1) · added by Fern
  • Or, Lehmann, Shahraeeni & Shokri (2013), Vadose Zone Journal 12(4): Stage II rate is controlled by diffusion through the dry layer and is much lower than the atmospheric demand. (confidence 0.8)
Organic mulch or litter cover cuts soil evaporation, by about 5 percent per 10 percent of surface covered
Litter layerCrop residueWaterPlant litter
Evidence (1) · added by Fern
  • Allen et al. (1998), FAO Irrigation and Drainage Paper 56, ch. 7 and 11: FAO-56 reduces the soil evaporation coefficient by 5 percent for each 10 percent of surface covered by mulch. (confidence 0.65)
Capillary rise from a water table: fringe height is about 0.15 cm2 divided by the pore radius, from roughly 0.1-0.3 m in coarse sand to over 1.5 m in silt and clay
GroundwaterCapillary forcesWaterPore space
Evidence (1) · added by Fern
  • Hillel (1998), Environmental Soil Physics, Academic Press, ch. on capillarity: Capillary rise height is inversely proportional to pore radius (h about 0.15 cm2 over r), so finer soils lift water higher. (confidence 0.75)
Shallow saline groundwater delivers dissolved salts to the surface where evaporation leaves them behind
GroundwaterSoluble saltsSaltWaterSodium
Evidence (1) · added by Fern
  • Rengasamy (2006), World salinization with emphasis on Australia, Journal of Experimental Botany 57:1017-1023: Rising saline water tables and capillary rise are the main cause of dryland salinity in Australia. (confidence 0.75)
Salt crust and accumulated salts lower the soil water potential and add a further barrier to loss
Soluble saltsSoil surfaceSaltWater vapour
Evidence (1) · added by Fern
  • Nachshon, Weisbrod, Dragila & Shokri (2011), Coupling water and salt dynamics in evaporating porous media, Geophysical Research Letters: Salt precipitation at the surface can slow evaporation by forming a crust. (confidence 0.45)