What might cause an increase in friction loss within an irrigation system?

An increase in friction loss within an irrigation system can occur due to increased flow rate through narrower fittings. As water flows through a pipe, the friction between the water and the inner surface of the pipe creates resistance, which can be compounded when the flow rate increases. When fittings or pipes are narrower, they offer less space for the water to move through, increasing the velocity of the water. Higher velocity encounters more resistance with the pipe walls, resulting in greater friction loss.

Choosing larger diameter pipes would typically reduce friction loss, not increase it, as would lower water temperature, which generally decreases viscosity and also reduces energy losses during flow. Increased water viscosity, while it can affect flow characteristics, is not the primary factor in the context of this question, focusing on the effects of flow and pipe size in generating frictional resistance. Thus, increased flow rate through narrower fittings is the most accurate reason for an increase in friction loss within an irrigation system.