Penman-Monteith-Leuning Evapotranspiration In Google Earth Engine

Modeling framework

Penman-Monteith-Leuning model (abbreviated as PML_V1) was proposed by Leuning et al. (2008), and further improved by Zhang et al., (2010, 2016). In PML, evaporation is divided into: transpiration from vegetation (Ec), direct evaporation from the soil (Es) and vaporization of intercepted rainfall from vegetation (Ei).

PML_V2 was developed by Gan et al., (2018) and Zhang et al., (2019), which coupled ET and gross primary products via canopy conductance theory. They are both in the resolution of 500 m and 8-day, and range from -60°S to 90°N.

Figure 1. Flowchart of global forcing data processing and PML_V2 modeling processes.

Variable	Description	Unit
Tmax	daily maximum temperature	°C
Tmin	daily minimum temperature	°C
Tavg	daily mean temperature	°C
Pa	atmosphere pressure	kPa
U	wind speed at 10-m height	m/s
q	specific humidity	kg/kg
Prcp	precipitation	mm/d
Rln	inward longwave solar radiation	W/m2
Rs	inward shortwave solar radiation	W/m2
Pi	the difference of Prcp and Ei	mm/d
Es_eq	equilibrium evaporation	mm/d
ET_water	evaporation from water body, snow and ice	mm/d
qc	quality control variable for albedo and surface emissivity.	-

Data product

Table 1. PML_V1 and PML_V2 bands information (PML_V1 have no GPP band, other bands are some).
Note: Only PMLV1 is available currently.

BandName	Units	Scale	Description
GPP	gC m-2 d-1	0.01	Gross primary product
Ec	mm d-1	0.01	Vegetation transpiration
Es	mm d-1	0.01	Soil evaporation
Ei	mm d-1	0.01	Interception from vegetation canopy
ET_water	mm d-1	0.01	Water body, snow and ice evaporation. Penman evapotranspiration is regarded as actual evaporation for them.
qc	-	-	Interpolation information for Albedo and Emissivity. Bitmask for qc: Bits 0-2: Emissivity interpolation information 0: good value, no interpolation 1: linear interpolation 2: history 8-day average interpolation 3: history monthly average interpolation Bits 3-5: Albedo interpolation information Same as Emissivity.

1.1 Access data

Click the following links to get the access. The corresponding links are:

1.2 Data download

PML products are standard ee.ImageCollection object in GEE. You can clip regional data by polygon shapefile from ee.ImageCollection.

Upload your polygon shapefile to GEE https://developers.google.com/earth-engine/importing
Download data from GEE
https://developers.google.com/earth-engine/exporting

For small regions, you can transform ee.ImageCollection into multiple bands ee.Image. In this way, you can download all the dataset in a time:
For large regions, you have to download trough ee.ImageCollection.

Clip and export the regional data you need by the polygon shapefile you uploaded. This is a little example.

References: