gddPy

Description

This Python library is intended for agriculture professionals interested in calculating growing degree days (GDD). GDD is also known as heat units or thermal units.

Installation and Initial Usage

To begin using the library, install it using one of the following commands based on your system and package management strategy:

pip install gddPy
pip3 install gddPy
poetry add gddPy

Next, here's a quick example of using the library:

from gddPy import GDD

gdd = GDD()
gdd.min_temp = 34
gdd.max_temp = 60
gdd.threshold_low = 40

heat_units = gdd.calcDailyAverage() # should calculate to 7

Detailed Description

The library supports the following properties:

Each property may be set when creating a new GDD() instance as a dictionary property

params = {
    "min_temp": 34,
    "max_temp": 60,
    "threshold_low": 40
}

gdd = GDD(params)

The following calculation methods are supported, each with a description of the formula

DailyAverage

The Daily Average method is the simplest approach to calculate GDD. The formula takes the average temperature for the day and subtracts the lower threshold from it¹.

$\text{GDD} = \frac{T_{\text{max}} + T_{\text{min}}}{2} - TH_{\text{low}}$

Baskerville-Emin

The Baskerville-Emin method is a more complex approach to calculate GDD that is preferable in regions with larger temperature fluctuations².

$\text{GDD} = \frac{w \cdot \sqrt{1 - \left(\theta\right)^2} - (TH_{\text{low}} - T_{\text{avg}}) \cdot \arccos\left(\theta\right)}{\pi}$

where...

• $w =$ Half of the Daily Temperature Range
• $T_{\text{avg}} =$ Average Temperature
• $TH_{\text{low}} =$ Lower Threshold
• $\theta = \frac{TH_{\text{low}} - T_{\text{avg}}}{w}$

Hourly Utilization

The Hourly Utilization method is a more precise approach to calculate GDD that requires hourly temperature readings to determine the thermal accumulation for each hour individually.

$\text{GDD} = \frac{\sum_{h=1}^{24} \max\left( T_{h} - TH_{\text{low}}, 0 \right)}{24}$

Although the formula above assumes a whole day (24 hours) this library is able to calculate partial days by providing less than 24 temperature values to hourly_temps

gdd = GDD()
gdd.threshold_low = 34
gdd.hourly_temps = [32,36,51,60,74,75,70,66,63,61]

heat_units = gdd.calcHourlyUtilization()

Using min_temp_cutoff and max_temp_cutoff

To use min_temp_cutoff and/or max_temp_cutoff, pass a dictionary to any calculation method setting flags to True.

temperature_data = {
    "min_temp": 34,
    "max_temp": 60,
    "min_temp_cutoff": 35,
    "max_temp_cutoff": 55,
    "threshold_low": 40
}

gdd = GDD(temp_data)

params = {
    "cutoff_min_temp": True,
    "cutoff_max_temp": True
}

heat_units = gdd.calcDailyAverage(params) # equals 5

Changelog

• v1.0.3 | January 30, 2024: Added calcHourlyUtilization() method, which requires threshold_low and hourly_temps to be set. Added two properties min_temp_cutoff and max_temp_cutoff that can be used with any of the calculation methods by passing use_min_cutoff = True or use_max_cutoff = True