What Thornthwaite Potential Evapotranspiration represents
The method derives exponent a from annual heat index, then scales a temperature power law for mean daylight and month length.
Thornthwaite Potential Evapotranspiration begins with monthly mean temperature, annual heat index i, mean daylight duration, days in month. Label each input as observed, homogenized, modeled, assumed, or derived, and preserve its site, spatial support, calendar period, reference interval, and aggregation method.
Boundary and sanity checks
Annual heat index must be positive; this formulation uses positive monthly temperature.
Change one Thornthwaite Potential Evapotranspiration input at a time and predict the response. This exposes reversed frost dates, inclusive-versus-exclusive duration errors, zero denominators, mismatched Celsius and Kelvin, and threshold equality mistakes. For Thornthwaite Potential Evapotranspiration, also record how leap days, trace values, incomplete periods, ties, and endpoint inclusion were handled so later recalculation uses the same climate convention.
Where the climate model stops
Wind, humidity, radiation, advection, elevation, and surface properties are absent, and warm arid climates can be biased.
Thornthwaite Potential Evapotranspiration is transparent arithmetic, not an official climate normal, drought declaration, seasonal forecast, attribution study, agricultural recommendation, water allocation, or operational safety authority.
Normals, anomalies, and standardization
A normal is a defined reference-period average; an anomaly subtracts a reference; a standardized value also divides by reference variability. Thornthwaite Potential Evapotranspiration must retain which operation and period were used.
Rebaselining can change a Thornthwaite Potential Evapotranspiration anomaly without changing the observation. Mixing reference means or standard deviations from different periods breaks the intended comparison.
Probability and percentile conventions
Percentiles in Thornthwaite Potential Evapotranspiration depend on sample, tie handling, and empirical ranking. Date probabilities additionally depend on the selected distribution and whether the event is defined as occurring by or after a target date.
A 50% fitted Thornthwaite Potential Evapotranspiration probability at a mean date is not a deterministic forecast. Climate nonstationarity and small tail samples can make historical probabilities poor descriptions of a future year.
Continue the Thornthwaite Potential Evapotranspiration workflow with the related Snow Season Length Calculator, retaining the same calendar, reference period, and dataset support.
Water balance and PET conventions
Precipitation, PET, actual evapotranspiration, runoff, and soil storage are distinct. Thornthwaite Potential Evapotranspiration should preserve the PET method because Hargreaves, Thornthwaite, and physically based methods can disagree.
Annual ratios inside Thornthwaite Potential Evapotranspiration hide seasonality. The same annual precipitation and PET can accompany very different monthly water availability, snow storage, and ecosystem response.
Formula and unit path
The working relationship is PET = 16(L/12)(N/30)(10T/I)^a. Thornthwaite Potential Evapotranspiration uses only displayed inputs and retrieves no station series, gridded data, normals, forecasts, or climate classifications.
Carry temperature scale, precipitation depth, day-of-year calendar, duration, and denominator units through Thornthwaite Potential Evapotranspiration. Keep an absolute anomaly separate from a standardized anomaly, and keep a fitted probability separate from an observed frequency.
Checked numerical example
At 20°C, heat index 50, 12 daylight hours, and 30 days, PET is approximately 117.14 mm/month.
Reset restores this Thornthwaite Potential Evapotranspiration example. Repeat it independently with the stated threshold, endpoint, tie, or distribution convention before substituting climate observations.
Assembling compatible climate inputs
Use monthly mean temperature, annual heat index computed from the same climate series, astronomical daylight, and actual month length.
For Thornthwaite Potential Evapotranspiration, record station or grid identifier, coordinates, elevation, dataset version, valid calendar, reference period, missing-data rule, homogenization status, spatial weighting, units, and quality flags as applicable.
Representativeness and record changes
Climate statistics summarize repeated weather over a declared record. One Thornthwaite Potential Evapotranspiration dataset can change when station exposure, instruments, processing, land cover, or spatial grids change.
When combining Thornthwaite Potential Evapotranspiration sources, retain individual values and justify weights so coverage differences, discontinuities, and uncertainty remain visible.
Interpreting Thornthwaite monthly PET
The output is empirical climatic PET and is conventionally zero for nonpositive monthly temperature; this interface models positive temperatures.
Compare Thornthwaite Potential Evapotranspiration outputs only after aligning variable definition, temporal scale, season, reference record, threshold, distribution method, and spatial support. Similar numbers can represent different climate constructs.
Continue the Thornthwaite Potential Evapotranspiration workflow with the related Climatological Normal Average Calculator, retaining the same calendar, reference period, and dataset support.
Frequent climate-calculation errors
Typical Thornthwaite Potential Evapotranspiration errors include averaging averages with unequal support, counting missing precipitation as zero, mixing calendar and water years, using maximum width instead of mean, or fitting a trend from only selected endpoints.
Reject impossible Thornthwaite Potential Evapotranspiration combinations rather than forcing an answer. Preserve true zero, trace, censored, and missing states separately; keep threshold equality explicit; and test whether the result changes when the reference period changes.
Climate calculation questions
Can forecast or scenario values be entered?
Yes. Label the Thornthwaite Potential Evapotranspiration output as a scenario; the page does not fetch or validate a forecast.
How can I verify Thornthwaite Potential Evapotranspiration?
Repeat PET = 16(L/12)(N/30)(10T/I)^a with recorded conversions, then test the checked example and a boundary.
Why could an official source differ?
Official products may use different station histories, grids, reference periods, missing-data rules, distributions, PET methods, thresholds, or rounding than Thornthwaite Potential Evapotranspiration.