WayBeyond’s Optimized series is all about turning insights into impact. 

Last month we showed how a tomato grower used reference evapotranspiration (ETo) forecasting to reduce water use by 16%—without compromising yield or fruit quality.

In this post, we’ll dive deeper into how ETo forecasting helps growers plan daily irrigation with greater accuracy. Whether you’re managing substrate-grown crops in greenhouses or high-value protected cropping rows, ETo-based irrigation ensures your plants get what they need—and nothing they don’t.

Understanding ETo Forecasting

Reference Evapotranspiration (ETo) measures the amount of water a reference crop would lose to evaporation and transpiration. This value is calculated based on climate conditions like temperature, humidity, wind speed, and solar radiation. ETo helps you understand how much water your crops are losing to the environment, and more importantly, how much water they need to stay healthy.

Using ETo forecasts takes it a step further: it lets you predict crop water demand based on real-time, localized climate data. This means that instead of relying on guesswork or past experiences, you can adjust your irrigation schedule to the current needs of your crops, day by day.

How ETo Forecasting Improves Irrigation Planning

Adopting precision irrigation means planning water use more accurately and efficiently. ETo forecasting improves this process in several ways:

1. Proactive Irrigation Scheduling

Instead of waiting for visual stress signals or soil moisture alerts, ETo forecast data lets you anticipate water needs up to 48 hours ahead. This allows irrigation to be scheduled during optimal windows (like early morning) to prevent crop stress.

2. Adjusting for Weather Variations

Weather plays a major role in how much water your plants need. On cloudy or humid days, plants lose less water than on sunny, windy days. ETo forecasts automatically adjust for these weather changes, helping prevent overwatering during low-demand periods and ensuring an adequate supply during high-stress days.

3. Irrigation for Different Crop Stages

Not all plants need the same amount of water at every growth stage. A tomato plant in fruit development has different water needs than one in the vegetative phase. With ETo forecasting, you can adjust water delivery based on crop coefficients (Kc), fine-tuning irrigation to each crop’s specific requirements.

4. Optimizing Root Zone Moisture

ETo forecasting helps you match irrigation frequency to the actual uptake rates of your plants. This prevents substrate oversaturation while maintaining optimal moisture levels in the root zone.

5. Improving Resource Efficiency

Watering based on plant demand using ETo forecast data helps reduce nutrient leaching, minimize disease risks from excess moisture, and ensure consistent crop quality. The result? More efficient use of water and fertilizers, leading to healthier, more productive crops

Why It Matters

ETo forecasting helps growers from fixed watering schedules to precision irrigation. It’s not just about saving water. It’s about optimizing every input, protecting quality, and maximizing ROI.

Get ETo Forecasts with FarmRoad

FarmRoad provides hourly ETo forecasts directly in the Irrigation Forecast dashboard. These values reflect the expected evapotranspiration based on your local climate conditions. This means you can accurately estimate the daily or hourly water demand of your crops, making it simpler to plan irrigation decisions with confidence.

Smarter irrigation starts with one shift: using what you already know—climate data—to do more with every drop. Want to see how ETo can work with your setup? 

Contact our team to get started