What Affects The Rate Of Water Loss In Plants?

The rate of water loss (transpiration) depends on evaporation. Therefore anything that affects the rate of evaporation would also affect the rate of water lost. Some of the factors that affect this in plants are as follows:

Humidity in Air: The inter cellular spaces within the leaf are usually over filled with water vapor. If the air outside is dry, water vapor from the leaf will spread out at a faster rate. Thus the rate of transpiration would be greater. If the air outside is humid evaporation will be hindered and the leaf will transpire less.  Assuming, the other factors are constant, the rate of transpiration decrease with increasing humidity.

Temperature of the Air: Leaves transpire more in hot weather conditions.

Strong Wind:  As leaves lose water due to transpiration, the air outside gets damp. If a wind is blowing, this water vapor gets blown away, making the air around the leaf less damp.  A leaf loses more water in high winds.  However, if the wind is blowing too fast the stomata may shut down to prevent too much loss of water.

Light: Since light affects the size of the stomata of the leaf. It therefore also has an affect on the rate at which a leaf loses water. During the day, the stomata get wider.  This increases the rate of transpiration. At night, the stoma closes down.