This data was produced in collaboration with The Wilderness Society.
This set of files includes downscaled historical estimates of decadal means of seasonal total potential evapotranspiration (in millimeters, no unit conversion necessary) for each season of every decade from 1910 - 2006 at 2x2 kilometer spatial resolution. Each file represents a mean seasonal total in a given decade.
The four seasons are referred to by the first letter of 3 months making up that season.
JJA=summer
SON=fall
DJF=winter
MAM=spring
The spatial extent includes Alaska.
These potential evapotranspiration (PET) estimates were produced using the Hamon equation (Lu et al. 2005), which calculates PET as a function of temperature and day length. Potential evapotranspiration may also be influenced by cloud cover, humidity, and wind speed. The Hamon equation can not explicitly account for variability in these aspects of weather and climate, so it may over or underestimate changes in PET if humidity, cloud cover, or wind speeds change substantially. In addition, the Hamon equation was developed to calculate daily potential evapotranspiration, and so these estimates, based on monthly data, may differ from those calculated from daily data.
Please see the associated document Hamon_PET_equations.pdf for the equations used. Scripts used for the calculation are available upon request to SNAP.
Lu, Jianbiao; Sun, Ge; McNulty, Steven G.; Amatya, Devendra (2005). A comparison of six potential evaportranspiration methods for regional use in the southeastern United States. Journal of the American Water Resources Association, 41, 621- 633.
Each set of files utilizes data from the Climatic Research Unit (CRU, http://www.cru.uea.ac.uk/) TS 3.0 dataset which was downscaled to 2km by the Scenarios Network for Alaska and Arctic Planning.
=============================
Downscaling:
The input temperature files are bias corrected and downscaled via the delta method using PRISM (http://prism.oregonstate.edu/) 1961-1990 as baseline climate. Absolute anomalies are utilized for temperature variables. Proportional anomalies are utilized for precipitation variables.
For more detailed information on base input data (GCMs, historical data), emission scenarios, the downscaling process, or uncertainty, please go to http://www.snap.uaf.edu/
===================
File naming scheme:
While it’s hard to have a completely static file naming scheme, we make every attempt to keep some consistency across our various datasets. This naming scheme outlined below is our general guide, although it does vary depending upon each dataset.
[variable]_[metric]_[units]_[format]_[assessmentReport]_[groupModel]_[scenario]_[timeFrame].[fileFormat]
some examples of these file names parts include:
[variable] pr, tas, logs, dot, dof, veg, age, dem
[metric] mean, total, decadal mean monthly mean
[units] mm, C, in, km
[format] optional, if layer is formatted for special use
[assessmentReport] ar4, ar5 (assessment report, for projected data only)
[groupModel] cccma_cgcm31, mpi_echam5, gfdl_cm21, ukmo_hadcm3, miroc3_2_medres, 5modelavg, cru_ts31
[scenario] sresb1, sresa2, sresa1b
[timeFrame] yyyy or mm_yyyy or yyyy_yyyy or mm_yyyy_mm_yyyy
[fileFormat] tif, txt, png, pdf
=======================
full file name examples:
tas_mean_C_ar4_cccma_cgcm3_1_sresb1_05_2034.tif
This file represents May 2034 mean temperature in degrees Celsius from the 4th Assessment Report on Climate Change from the CCCMA modeling group, using their CGCM3.1 model, under the B1 climate scenario.
pr_decadal_mean_DJF_total_mm_cru_TS31_historical_1920_1929.tif
This file represents mean total winter(Dec, Jan, Feb) precipitation from 1920-1929 from downscaled CRU TS 3.1 data.
pet = potential evapotranspiration
tas = near-surface air temperature
pr = precipitation including both liquid and solid phases
dof = day of freeze
dot = day of thaw
logs = length of growing season