Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Water movement / Evapotranspiration partitioning (about 61 percent transpiration, range 35-90)
Evapotranspiration partitioning (about 61 percent transpiration, range 35-90)
How the water that returns to the air from land splits into plant transpiration, soil evaporation, canopy interception evaporation and open-water or snow loss. Each kilogram evaporated absorbs about 2.45 MJ of latent heat.
Boundary: where this process starts
Starts with: Net radiation and vapour pressure deficit supply energy of 2.45 MJ per kg water evaporated
Boundary: where it ends
Ends after: Wet canopy and litter evaporate intercepted water (about 10 percent of ET); Lakes, snow and wet surfaces evaporate or sublimate (about 4 percent)
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.
Net radiation and vapour pressure deficit supply energy of 2.45 MJ per kg water evaporated
Evidence (1) · added by Quanta
- Schlesinger 2014, Transpiration in the global water cycle, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2014.01.011: Land ET returns roughly 60 percent of land precipitation to the air, consuming a large share of net radiation as latent heat. (confidence 0.55)
⑂ Fate of evapotranspired water
Evidence (1) · added by Quanta
- Schlesinger 2014, Transpiration in the global water cycle, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2014.01.011: Transpiration roughly 61 percent of ET; rest is soil, interception and open water evaporation. (confidence 0.6)
Stomata open and roots lift water to leaves (0.5-5 mm per day per ground area)
Evidence (1) · added by Quanta
- Jasechko 2013, Terrestrial water fluxes dominated by transpiration, Nature, doi:10.1038/nature11983: Isotope and flux compilations show transpiration is the largest single terrestrial water flux; estimates 35-90 percent of ET depending on method. (confidence 0.6)
Bare soil evaporates in two stages: energy-limited (3-6 mm per day), then diffusion-limited
Evidence (1) · added by Quanta
- Brady and Weil, The Nature and Properties of Soils (15th ed.), chapters on soil water and soil formation (textbook, no DOI): Two-stage soil evaporation (constant-rate then falling-rate) described in soil physics texts; rates are typical field ranges. (confidence 0.5)
Wet canopy and litter evaporate intercepted water (about 10 percent of ET)
Evidence (1) · added by Quanta
- Schlesinger 2014, Transpiration in the global water cycle, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2014.01.011: Interception is of the order of a tenth of ET (estimate 5-15 percent). (confidence 0.45)
Lakes, snow and wet surfaces evaporate or sublimate (about 4 percent)
Evidence (1) · added by Quanta
- Schlesinger 2014, Transpiration in the global water cycle, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2014.01.011: Open water and snow are a small share of terrestrial ET (estimate 2-8 percent). (confidence 0.4)
Root-zone water potential falls toward the wilting point (-1.5 MPa)
Evidence (1) · added by Quanta
- van Genuchten 1980, A closed-form equation for predicting the hydraulic conductivity of unsaturated soils, Soil Science Society of America Journal, doi:10.2136/sssaj1980.03615995004400050002x: Retention curve spans field capacity (about -33 kPa) to permanent wilting (about -1500 kPa). (confidence 0.6)
Moisture recycled to the air returns as rain downwind (about 40 percent of continental rain is locally recycled)
Evidence (1) · added by Quanta
- van der Ent 2010, Origin and fate of atmospheric moisture over continents, Water Resources Research, doi:10.1029/2010wr009127: Continental precipitation recycling ratios of roughly one tenth to over a half depending on region and scale; global continental mean around 40 percent. (confidence 0.5)