How does this relate to agriculture?
Farmers are responsible for maintaining a majority of the cropland vegetation in arable regions of the world. Vegetation (or the lack of it) is a key factor affecting weather patterns and micro-climates. The following factors are affected by vegetation:
|Figure C: Bradford Pear Orchard|
Image from Bridget Lassiter
(1) Plant covers and crops are inherently responsible for a vast majority of the water storage and usage. When irrigation is taken out of the equation, rain, snow, fog, dew, frost and soil water are all used and captured by vegetation. Some of this water is intercepted by the leaves themselves, and some of the water that infiltrates the soil is absorbed by plant roots. When water is available in excess, plants can transpire large volumes of water as a by-product of photosynthesis. This in turn causes evaporative cooling in the atmosphere directly surrounding the crop.
(2) Vegetation contributes to the level of carbon dioxide that is present in the atmosphere. Seasonal variations have shown that higher levels of CO2 are measured in the early-mid part of the growing season. There are also daily variations in CO2, with the highest levels measured during the day.
(3) Radiation measurements within a crop or vegetated area reveal a complex relationship between absorption, reflection, transmission and emission. The albedo of a crop is lower than the sum of all of the leaves in the canopy due to differences in crop architecture and angle of solar radiation. Most individual leaves have an albedo of about 0.25, but the albedo for a crop is less and depends upon crop height. For a crop of 1m in height, the surface albedo is between 0.18 and 0.25. However, this value is dependent upon the vegetation type. If leaves are wilted, or if the soil is exposed beneath the canopy this value can be different. Also, this albedo measurement is the one taken at mid-day. Early morning and late day measurements of albedo are much higher and the values follow the position of the sun in the sky. Also, tropical measurements of albedo are usually less that for a similar vegetated surface found at higher latitudes.