No one likes to see the sprinklers on when it is raining. Rain shut-off devices can fix that. But the bigger problem is, they don’t know how much rain fell or when to resume watering after the storm is over. Also rain shut-off devices allow watering in light rain storms.
Irrigation supplements rainfall. Water managers should consider both ET and rainfall. Very simply ET – Rain = Irrigation. It would be nice if it was that simple. The problem is not all rainfall is effective. Rain needs to reach the plants. In a heavy rain storm water runs off. Long sustained rain will soak below roots, so how much rain can the soil hold?
Traditional Smart controllers measure ET and use rain shut-off devices. Smarter irrigation controllers measure both ET and rain, and then quantify how much rain is effective. To ignore heavy rain that falls faster than the soil can absorb, smarter controllers consider soil percolation rates. Smarter controllers also use a running moisture balance to quantify soil holding capacities and current soil moisture content. The moisture balance method is often compared to a check book; ET withdraws water from the soil, rain and irrigation are deposits. But the soil moisture reservoir has a limited capacity. Smarter irrigation controller respect these limits so they can irrigate when the plants need water.
To see the affects of each of these factors here are examples of soil moisture balances over 2 weeks under a variety of circumstances:
A couple small storms in June – watering is only needed twice
Heavy storm – no irrigation is needed.
Light sustained drizzle – no irrigation is needed.
Summer thunder storm – watering is needed 3 times
Rainfall effectiveness can be increased in several ways. The most beneficial is to increase the root zone storage capacity. This is done by promoting deeper roots through deep, less frequent watering. Roots stay shallow in overwatered landscapes because they need air.
Landscape water management is a complex process. The technology in smarter irrigation control systems simplifies this process. Climate controlled irrigation reacts automatically to changing weather conditions. Water bills come down because wasteful overwatering is reduced. There is a tremendous time savings because you don’t need to reprogram sprinkler timers when the weather changes.