Methods

Data Collection

Weather station precipitation data was collected from Castellanos-Acuna and Hamann (2020)
Weather station temperature data was collected using similar methodology to that outlined in Castellanos-Acuna and Hamann (2020). Data was aggregated from five public databases:
1. Climate Research Unit (CRU) database v3 (Harris et al., 2014)
2. Global Historic Climate Network Monthly (GHCN-M) database v3 (Lawrimore et al., 2011)
3. Global Historic Climate Network Daily (GHCN-D) database v3 (Menne et al., 2012)
4. World-wide Agroclimatic Data of FAO (FAOCLIM) database v2 (FAO, 2001)
5. World Meteorological Organization (WMO) database (WMO, 1996)
Weather station data observations are aggregated 30 year normal period averages (1991-2020)
Interpolated weather station data was generated using ClimateNA software (Wang et al., 2016).

Level 4e ecozone designations were created by adding elevation bands to existing level 4 ecozone boundaries.
Ecozone points were systematically sampled from a database containing 5-kilometer grid points across North America to ensure each ecozone was adequately represented in the sample. This subsampling was performed to reduce computational demands during the analysis while retaining ecozone representation.
Climate estimates for weather station locations and selected ecozone points were generated using ClimateNA software (Wang et al. 2016).
Weather stations were then spatially joined with Level 4e ecozone polygons to assign the appropriate ecozone codes to each weather station location.

Figure 1. A visualization of the sampling design used in this study.

Below are the suite of annual climate variables generated by ClimateNA used in this study:

Directly calculated annual variables:

MAT: mean annual temperature (°C)

MWMT: mean warmest month temperature (°C)

MCMT: mean coldest month temperature (°C)

TD: temperature difference between MWMT and MCMT, or continentality (°C)

MAP: mean annual precipitation (mm)

AHM: annual heat-moisture index (MAT+10)/(MAP/1000))

SHM: summer heat-moisture index ((MWMT)/(MSP/1000))

Derived annual variables:

DD<0 (or DD_0): degree-days below 0°C, chilling degree-days

DD>5 (or DD5): degree-days above 5°C, growing degree-days

DD<18 (or DD_18): degree-days below 18°C, heating degree-days

DD>18 (or DD18) : degree-days above 18°C, cooling degree-days

NFFD: the number of frost-free days

FFP: frost-free period

bFFP: the day of the year on which FFP begins

eFFP: the day of the year on which FFP ends

PAS: precipitation as snow (mm). For individual years, it covers the period between August in the previous year and July in the current year

EMT: extreme minimum temperature over 30 years (°C)

EXT : extreme maximum temperature over 30 years (°C)

Eref: Hargreaves reference evaporation (mm)

CMD: Hargreaves climatic moisture deficit (mm)

MAR: mean annual solar radiation (MJ m‐2 d‐1)

RH: mean annual relative humidity (%)

CMI: Hogg’s climate moisture index (mm)

DD1040: degree-days above 10°C and below 40°C

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