Humidity as an Abiotic Factor at Race Rocks
|The present Humidity measured by a sensor 1.5 metres above the rock surface at Race Rocks.||Humidity in concert with Temperature, Sunlight and Wind is an important factor which all organisms have to tolerate or adjust to at Race Rocks. The humidity changes widely in a number of micro ecosystems, even in the intertidal area, such as in crevices and under vegetation.|
|Graph of today’s humidity at Race Rocks.||The humidity for the past week. Click on the above graphs for larger versions||The preceding month humidity record . These three graphs represent historical records of atmospheric pressure at different time scales. This graphical interpretation is made possible by the website victoriaweather.ca|
The following are some of the derived variables which involve humidity in their calculations. For an Advanced explanation of the derived variables such as wind chill, ET, heat Index, etc. See this link.
|The present Heat Index, calculated from sensors 1.5 metres above the rock surface at Race Rocks.||Data: Heat Index
The Heat Index, also knows as the Temperature/humidity index (THI) uses the temperature and the relative humidity to determine how hot the air actually “feels.” When humidity is high (i.e., the air is saturated with water vapor) the apparent temperature will be higher than the air temperature because perspiration cannot readily evaporate into the surrounding air.
Technically, Heat Index is calculable only when air temperature is above 68 °F (20 °C) because it is a measure of heat stress, which is not significant at lower temperatures. Davis Instruments smoothes the curve relating air temperature to Heat Index between 68 ºF (20 ºC) and 57 ºF (13.9 ºC). Below 57 ºF (13.9 ºC), the Heat Index is equal to outside temperature. Conversely, 135 °F (52 °C) is the highest Heat index for which calculation factors are available. Note that at very low humidity values, the air temperature can be as high as 140 ºF.
In terms of storage to the data logger and database, Heat Index is a special case. It is not stored in archive memory or in the database, rather it is calculated as necessary (for example, when plotting or displaying database information). When Heat Index data is needed, the software calculates an average for each archive interval based on the temperature and humidity readings for the archive period.