Difference between revisions of "Growing Degree Day"
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T<sub>base</sub> = temperature below which plant growth is zero.<br> | T<sub>base</sub> = temperature below which plant growth is zero.<br> | ||
| − | In addition to T<sub>base</sub>, each plant species has its own upper | + | In addition to T<sub>base</sub>, each plant species has its own upper air temperature threshold, T<sub>max</sub>. |
| − | air temperature threshold, T<sub>max</sub>. | + | At temperatures above T<sub>max</sub>) the plant does not grow any faster. T<sub>max</sub> varies for each species. |
| − | At temperatures above T<sub>max</sub>) the plant does not grow any faster. | + | |
| + | One method of approximating GDD is the average of the daily maximum and minimum temperatures above T<sub>base</sub>. | ||
| + | |||
| + | [[File:GDD average.png|frameless|center|400px]] | ||
Revision as of 15:47, 25 November 2018
Plants grow in a cumulative stepwise manner which is strongly influenced by ambient temperature. Growing Degree Days (GDD), also called Growing Degree Units (GDU) or Heat Units (HU), are based on the observation that within limits, plants grow faster when warm and more slowly when cold. Below a base temperature (Tbase), the plant is dormant and little growth occurs. Since growth depends on the accumulation of specific quantities of heat, by accumulating Growing Degree Days it is possible to predict when events such as bud break (nectar flows) will occur during a growing season regardless of differences in temperatures from year to year.
where:
T = current temperature
Tbase = temperature below which plant growth is zero.
In addition to Tbase, each plant species has its own upper air temperature threshold, Tmax. At temperatures above Tmax) the plant does not grow any faster. Tmax varies for each species.
One method of approximating GDD is the average of the daily maximum and minimum temperatures above Tbase.
Different methods exist for calculating heat units depending on a) the crop or biological
organism of interest and b) the whim or personal preference of the researcher.
Growing degree day units are calculated by using the maximum daily air
temperature, the minimum daily air temperature and the crop’s lower
temperature threshold.
The method most commonly used in the U.S. for determining heat unit accumulation relative to corn phenology is the formula first suggested by the National Oceanic and Atmospheric Administration. The “modified growing degree day formula” calculates daily accumulation of GDD’s as the average daily temperature minus 50° F.
Calculate Growing Degree Day (GDD) for each hive and add to database.
Centigrade Tbase = 10 Tmax = 30
SET @gdd_total:=0; SELECT q1.doy, q1.gdd, round(@gdd_total := @gdd_total + q1.gdd) as gdd_tot FROM (SELECT DAYOFYEAR(DATE_FORMAT(`hive_observation_time_local`, '%Y-%m-%d')) AS doy, (least(greatest(max(wx_temp_c),10),30) - least(greatest(min(wx_temp_c),10),30))/2 AS gdd from HIVE_DATA where hive_id=10 group by DATE_FORMAT(`hive_observation_time_local`, '%Y-%m-%d') ) AS q1
SELECT hive_id, DAYOFYEAR(DATE_FORMAT(`hive_observation_time_local`, '%Y-%m-%d')) AS doy, (least(greatest(max(wx_temp_c),10),30) - least(greatest(min(wx_temp_c),10),30))/2 AS gdd from HIVE_DATA group by DATE_FORMAT(`hive_observation_time_local`, '%Y-%m-%d'), hive_id
