Evapotranspiration Data: What It Is and Why It Matters

Evapotranspiration (ET) is the combined process of water evaporating from soil and surfaces, plus water transpiring through plants. It represents the total amount of water that leaves the land surface and enters the atmosphere. Understanding ET is critical for irrigation planning, water resource management, drought monitoring, and ecological assessments.

Why Evapotranspiration Matters

Irrigation Planning

ET data tells farmers and agronomists how much water crops are losing to the atmosphere. The difference between rainfall and ET indicates the irrigation deficit: how much supplemental water is needed. Over-irrigating wastes water and money; under-irrigating reduces yields. ET data helps optimize both.

Water Resource Management

Water utilities and watershed managers use ET to calculate the water balance of a region. How much precipitation falls, how much evaporates, how much becomes runoff, and how much recharges groundwater. ET is typically the largest component of the water balance, often exceeding 60% of precipitation in warm climates.

Drought Monitoring

When ET significantly exceeds precipitation for extended periods, soil moisture depletes and drought conditions develop. Monitoring ET trends helps identify emerging drought before its effects become visible in crop health or water levels.

Ecosystem Health

ET is closely linked to vegetation health. Healthy, actively growing vegetation transpires more water. A sudden drop in ET can indicate vegetation stress, disease, or die-off before it becomes visible in satellite imagery or NDVI.

How to Read ET Values

PixelGust reports evapotranspiration in millimeters per year (mm/yr). Here are typical ranges:

• Deserts: 50-200 mm/yr (very little water is lost because there is very little water available)
• Grasslands: 300-600 mm/yr
• Croplands: 400-800 mm/yr (varies with crop type and irrigation)
• Forests: 500-1,200 mm/yr (highest ET due to large leaf area)
• Tropical rainforests: 1,000-1,500 mm/yr

Combining ET with Other Data

ET becomes more powerful when cross-referenced with other PixelGust datasets:

• Precipitation (Historical): Compare annual ET to annual precipitation. If ET > precipitation, the area relies on irrigation or groundwater.
• NDVI: High NDVI + high ET = healthy, actively transpiring vegetation. Low NDVI + low ET = barren or stressed area.
• Land cover: ET varies dramatically by land cover type. Cropland ET indicates irrigation intensity.
• Temperature: Higher temperatures drive higher potential ET. Climate warming means increasing ET and growing irrigation demands.

Use in Professional Workflows

Precision Agriculture

Modern farming uses ET data to schedule irrigation, ensuring crops receive the right amount of water at the right time. This saves water (typically 15-30% reduction), reduces energy costs for pumping, and improves crop quality.

Environmental Consulting

ET data is a required input for many environmental models, including groundwater recharge estimation, wetland delineation, and water balance assessments. PixelGust provides this data instantly without needing to download and process satellite imagery.

Renewable Energy

Solar farms on agricultural land must consider how panels affect ET. Agrivoltaic systems (where crops grow beneath solar panels) modify the ET balance, and understanding baseline ET is essential for designing these systems.

Data Source

PixelGust uses the MODIS MOD16A2 evapotranspiration product from NASA. This dataset provides ET estimates at 500-meter resolution, derived from satellite observations of land surface temperature, vegetation indices, and meteorological data. It is widely used in hydrology, agriculture, and environmental science research worldwide.