Data sources and delineation of GYGA-TEDs

Each GYGA-TED is a unique combination of a GYGA-CZ and water storage capacity in the rootable soil depth, the latter defining the root zone plant-available water holding capacity (RZPAWHC). GYGA-TEDs were created for Africa and US. The methodology used to develop the TEDs is described below. Details and uses of the TEDs are provided elsewhere (Rattalino Edreira et al., 2018; Andrade et al., 2019.

Africa GYGA-TED

Plant-available soil water holding capacity in the root zone was taken from the Africa Soil Information Service (AfSIS; http://www.isric.org/projects/afsis-gyga-functional-soil-information-sub-saharan-africa-rz-pawhc-ssa version April 2015, af_agg_ERZD_TAWCpF23mm__M_1km.tif, with a resolution of 1 × 1 km). RZPAWHC is determined by evaluation and spatial interpretation of the AfSIS soil profile database:

1. the so-called "legacy" soil point data (Africa Soil Profiles database v1.2;18,500 points) and
2. all AfSIS sentinel site soil point data (approx. 9,600 points, including spectral data and 10% wet chemistry reference data), which were provided by AfSIS for this collaboration,
3. SoilGrids1km layers (www.isric.org/explore/soilgrids) produced at ISRIC using global models; updated and fine-tuned fitting a continental model, with finer resolution satellite data and above mentioned soil data, resulting in AfrSoilGrids250m (www.isric.org/projects/africa-soilgrids-soil-nutrient-maps-sub-saharan-africa-250-m-resolution).

As a component of the GYGA-TED spatial framework, RZPAWHC values are classified into nine 25 mm classes, with =< 50 mm and >250 mm as lower and upper classes, respectively. 

This classification of the variables resulted in the following ranges:

RZWHC (mm)	RZWHC Value
0 - 50	100000
50 - 75	200000
75 - 100	300000
100 - 125	400000
125 - 150	500000
150 - 175	600000
175 - 200	700000
200 - 225	800000
225 - 250	900000
> 250	1000000

 

US GYGA-TED

Plant-available soil water holding capacity in the root zone was taken from gSSURGO database (Soil Survey Staff; Resolution of 250 × 250 m). There are two classifications, both based on the RZPAWHC values. For the fine TEDs the RZPAWHC values are classified into thirteen 25 mm classes, with 0-25 mm and >300 mm as lower and upper classes, respectively. For the coarse TEDs the RZPAWHC values are classified into seven 50 mm classes, with 0-50 mm as the lower class and >300 mm as the upper class. 

This classification of the variables resulted in the following ranges:

Some small areas within climate zones were considered irrelevant for technology transfer and removed from the original US GYGA-CZs scheme. Inclusions were removed when (i) they covered an area < 350,000 ha, (ii) the surrounding climate zone was, at least, 5 times larger, and (iii) standard deviation for terrain elevation was <10% (USDA-FSA-APFO, 2016). This rule aims to discard small inclusions attributable to an artefact of climate zones computations while keeping small CZ that portray microclimates caused by changes in temperature and precipitation due to complex topography. These refined climate zones were combined with the PAWR map to create the TED maps.   Values of the GYGA-TEDs Value for each cell indicates the unique combination of soil type and climate for that cell. The value of the GYGA-CZs is constructed by the sum of the three GYGA-CZ variables and for the GYGA-TEDs and the value of the RHWHC variable is added to the GYGA-CZ value. A few examples:

value 101001 =	GYGA-RZWHC value	100000
	GYGA-CZ Value GDD	1000 +
	GYGA-CZ Value AI	0 +
	GYGA-CZ Value Temperature seasonality	01
value 806801 =	GYGA-RZWHC value	800000
	GYGA-CZ Value GDD	6000 +
	GYGA-CZ Value AI	800 +
	GYGA-CZ Value Temperature seasonality	01
value 1010402 =	GYGA-RZWHC value	1000000
	GYGA-CZ Value GDD	10000 +
	GYGA-CZ Value AI	400 +
	GYGA-CZ Value Temperature seasonality	02

 

References

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