Evapotranspiration

Evapotranspiration describes how much water the garden loses through the soil and plants. The term combines evaporation (water evaporating from the soil and moist surfaces) and transpiration (water released by plants through their leaves). Together with rain and irrigation, this loss determines how quickly the root zone dries out and when water is needed again.

MIYO calculates evapotranspiration per irrigation zone, showing you the approximate water requirement of your zones under the current conditions. You can also find a more detailed product description at miyo.garden/pages/evapotranspiration.

What does this mean qualitatively?

More water evaporates on hot, sunny, and windy days; significantly less on cool, cloudy, or humid days. Dense vegetation evaporates mainly through its leaves, while open soil evaporates more through its surface. Dry soil also releases less water than moist soil—the plants and the soil surface then “throttle” the loss.

MIYO roughly estimates this daily water loss and converts it into an understandable figure (millimeters per day, where 1 mm ≈ 1 liter per m²). Typical values in Central Europe are often around 0.5–3 mm/day in spring and autumn, and more like 2–7 mm/day in summer—varying considerably depending on the weather and zone.

Which data is included?

For each zone, the calculation uses a combination of measurements, weather data at the location, and your garden settings.

1. Weather at the location

The weather data stored for your Cube (averages over the period considered, typically the last approx. 24 hours) includes, among other things:

• Air temperature
• Air humidity
• Air pressure
• Wind
• Cloud cover and visibility (indicating how strongly the sun gets through)
• Precipitation (rain during the period)

These variables describe the climate that drives or dampens evaporation.

2. Readings from the MIYO Sensor

If a soil moisture Sensor is assigned to the zone, MIYO uses, among other things:

• Soil moisture – how wet the soil currently is (drier soil → lower actual water loss)
• Sunlight / brightness – measured partly via the Sensor’s solar cell and brightness measurement, supplementing the weather data
• Temperature at the Sensor (as part of the overall picture in the system)

Without a Sensor, local weather data and your zone parameters remain the basis; moisture adjustment is then unavailable or more limited.

3. Settings for the irrigation zone

In the app, you enter the following for each zone, among other things:

• Soil type (e.g. sandy, loamy, clayey, mixed) – sandy soils store less water and tend to dry out faster, while clayey soils retain water longer
• Plant type (e.g. lawn, hedge, bed/crop, trees) – different plants and types of cover evaporate at different rates
• optional additional soil or garden properties, provided they are configured for the zone

The model also takes into account that plants’ water requirements fluctuate throughout the year (the growth phase in summer and dormant periods in winter).

Potential and actual evapotranspiration

MIYO broadly distinguishes between two levels:

• Potential evapotranspiration – how much water could evaporate at most if there were sufficient water in the soil (driven mainly by weather and radiation)
• Actual evapotranspiration – how much is approximately lost under real conditions when soil moisture, soil type, and vegetation are taken into account

When the soil is dry, the actual loss is often clearly below the potential maximum. It also takes into account that water can infiltrate deeper into the soil—to varying degrees depending on the soil and its moisture level.

What you can do with it in the app

You can view the calculated evapotranspiration for the past few hours/the previous day:

• monitor manually and adjust your watering to seasonal and weather-related fluctuations (MIYO will continue to fine-tune watering when rain is forecast or under similar conditions through the other automatic rules), or
• use automatically: In the watering settings for the zone, you can activate adjustment based on evapotranspiration. MIYO can then adjust the scheduled watering duration to the calculated demand (less in cool/humid weather, more when evaporation is high—within reasonable limits). Optionally, you can specify the values at which watering is reduced and whether minimum watering should still take place.

Evapotranspiration does not replace time windows, soil-moisture permission, or weather protection (rain, wind, …). It is an additional component that adjusts the quantity/duration of watering to the zone’s current water loss. Details on the automatic system’s decision logic can be found under Automatic watering.

Brief overview

Influence	Role in the model (qualitative)
Heat, sun, wind, dry air	higher water loss
Clouds, cool temperatures, high humidity, rain	lower demand / compensation through precipitation
Soil moisture (Sensor)	dry soil → less actual evaporation
Soil type	The zone’s water storage capacity and drying behavior
Plant type / season	how much the plants “drink” and provide cover
Infiltration	Water that drains downward beyond the root zone

This is how the app gives you a feel for why a hot, clear week in June requires significantly more water than a cool, cloudy day—and MIYO can control watering accordingly with greater precision.