Agmet EO Indicators Explained
The GEOGLAM-NASA Harvest Agrometeorological (AGMET) Earth Observation (EO) Indicators bring together a variety of Earth Observation (EO) data products on the sub-national scale, each of which provides valuable insights on in-season crop development and current crop conditions. Combined, each EO data plot helps tell the story of in-season crop conditions through the use of different climate, environmental, and vegetative variables. Detailed descriptions of the different components within the crop condition plots can be found below and in the corresponding NASA Harvest article. Further in-depth discussion on different EO data products for crop monitoring can be found on the EO Data page.
EO data plot components
Basic components
Within each plot, there are several main components. The light gray area shows the span of the most recent 10-year minimum and maximum values across the season in order to provide a better understanding of the particular EO data product’s variability over time. The black lines show the most recent 5-year mean values across the season in order to demonstrate what average conditions usually represent. The purple lines show what the values were across the previous season. The blue lines show what the values are for the current season in near real-time as the season progresses.
Crop Calendars
Each plot consists of four vertical lines to provide a reference for where crops are in the development stage, based on the GEOGLAM Crop Monitor crop calendars. The brown dotted line represents the planting stage, the green solid line represents greenup (the beginning of plant growth), the brown solid line represents senescence (late development stage), and the red dotted line represents the end of harvest. By examining the main components of each plot within the context of where crops are in their development cycle, analysts can better interpret how current conditions may impact the remainder of the season and final crop outcomes.
For more information about the crop calendars, please see the crop calendars section of the baseline data.
Normalized Difference Vegetation Index (NDVI)
There are two plots for NDVI. The first plot shows the NDVI values for the current season in comparison to the 5-year mean, values from the previous season, and the 10-year minimum and maximum values. As a crop season progresses, NDVI values will increase during early crop growth and development of leafy vegetation. NDVI will then reach the peak as the crop fully develops and reaches maturity, before senescence, and then decreases again as the crop matures and senesces as the leafy vegetation begins to die off. How the NDVI values progress over the course of the season and the individual peak values can help predict the productivity of the crops. The second NDVI plot shows the comparison of the current season NDVI values with the previous five seasons along with the resulting average crop yields from those seasons.
For more information on using NDVI data for crop monitoring please see the NDVI section of the EO Data.
Evaporative Stress Index (ESI)
The Evaporative Stress Index (ESI) estimates water loss due to evapotranspiration (loss of water from soil evaporation and from transpiration through plant leaves). The plot shows the current season’s values as compared to the 5-year mean, values from the previous season, and the 10-year minimum and maximum values. Negative values indicate below-normal evapotranspiration rates, representative of crops that are stressed due to inadequate soil moisture. ESI is good at identifying soil moisture deficits in the early stages and is able to capture flash droughts, which is the quick onset of drought brought on by periods of hot, dry, and windy conditions.
For more information on using evapotranspiration data for crop monitoring please see the Evapotranspiration section of the EO Data.
Precipitation
There are two plots for precipitation, both of which are measured in millimeters. The first plot shows the current season’s cumulative precipitation compared to the 5-year mean. When the cumulative precipitation goes above the 5-year mean, the area between the current values and the 5-year mean is colored in green to indicate above cumulative average rainfall. When the cumulative precipitation goes below the 5-year mean, the area between the current values and the 5-year mean is colored in red to indicate below average cumulative rainfall. In addition to recorded precipitation, the chart shows the 15-day forecast precipitation as a dot, either green or red to indicate if the forecast will place the cumulative precipitation up above or below the 5-year mean. The second plot shows the daily precipitation events for the season across time, helping to identify the evenness of rainfall over time or major rainfall events.
During the course of the season, the timing and the amount of rainfall surpluses or deficits can have different effects. As an example, too much rainfall during sowing can prevent farms from planting crops, and flooding events can cause dramatic yield reductions. Alternatively, not enough rainfall early in the season can prevent sown crops from emerging and properly developing.
For more information on using precipitation data for crop monitoring please see the Precipitation section of the EO Data.
Soil Moisture (Surface)
Surface Soil Moisture measures the amount of available water held in the top five-to-ten centimeters of the soil (depth dependent on soil texture). The first plot shows the current season’s surface soil moisture values as compared to the 5-year mean, values from the previous season, and the 10-year minimum and maximum values. Up to a maximum of 25 millimeters (mm) of available water is able to be held in the surface soil. Higher soil moisture values during the early development stage help crops to germinate and grow. Mid-range soil moisture values during the season help promote crop growth and root depth. However, lower values typically any time before senescence can cause stress in the crops and stunt development. Sub-surface soil moisture measures the amount of available water held below the surface layer from depths of ten and above centimeters. The second plot shows the same information the current season’s sub-surface soil moisture.
For more information on using soil moisture data for crop monitoring please see the Soil Moisture section of the EO Data.
Temperature
The temperature plot is measured in degrees Celsius and tracks the current season’s daily mean temperature as compared to the 5-year mean, values from the previous season, and the 10-year minimum and maximum values. Very high temperatures can affect crops in a number of ways such as the increase of water loss through increased evapotranspiration, slow plant growth, reduced yields, pollen abortion, and potentially thermal death. Very low temperatures can also affect crops through the slowing in crop growth, frost or chilling injury, reduced seed quality, and possible yield reductions.
For more information on using temperature data for crop monitoring please see the Temperature section of the EO Data.
AGMET Indicators taken as a whole
Example: 2021 Spring Wheat season in Alberta, Canada
In Alberta, Canada, the sowing of spring wheat typically occurs between early April to mid-May, depending on the part of the province. Based upon the AGMET chart for 2021, spring wheat began the season under generally normal conditions, albeit with reduced surface soil moisture as seen in the Soil water fraction (surface) sub-plot. During May, average to above-average precipitation was received, helping to support surface and sub-surface soil moisture levels along with the Evaporative Stress Index (ESI) values. However, beginning in mid-June, precipitation can be seen to drop off in both the cumulative and daily precipitation sub-plots, crossing below the 5-year mean. Shortly after the drop-off in precipitation, the surface and sub-surface soil moisture levels can be seen dropping below the 5-year mean and even below the 10-year Min/Max in the subplots. Additionally, the ESI can be seen to be dropping during this time and eventually crossing the zero level and the 5-year mean by the end of June, indicating that the crops are being stressed due to a lack of water.
During the last third of June, as precipitation continues to be below-average, the daily mean temperatures can be seen rising and going up above the 10-year Min/Max and then above 22°C, which is above wheat’s optimum temperature for flowering to grain-filling. Additionally, in the temperature subplot, many days with max temperatures above 30°C can be seen during late June and early July, which can reduce pollen viability in wheat and consequently grain yields. At this time, the NDVI can be seen diverging from the 5-year mean and dropping below the 10-year Min/Max in the NDVI subplot by the time it reaches its peak during mid-July. For most of the rest of the season through harvesting, which typically begins between early August to early September depending on the part of the province, precipitation, surface and sub-surface soil moisture, and ESI remain below-average.
As seen in the 2021 AGMET chart, the season began under generally normal conditions, but then beginning in June, a lack of precipitation and high temperatures impacted the crops. Based on data from Statistics Canada, the average yield for spring wheat in Alberta in 2021 was 2.231 tonnes per hectare, which was a 38% reduction from the previous 5-year (2016-2020) average, confirming a poor season for spring wheat in Alberta for 2021.
Data Sources
NDVI MODIS 8-day Climate Modeling Grid (CMG)-scale: https://ladsweb.modaps.eosdis.nasa.gov/archive/allData/61/MOD09CMG
Evaporative Stress Index (ESI): https://gis1.servirglobal.net/data/esi/
NOAA CPC Precipitation: https://downloads.psl.noaa.gov/Datasets/cpc_global_precip/
NOAA CPC Temperature: https://downloads.psl.noaa.gov/Datasets/cpc_global_temp/
Soil Moisture: https://nsidc.org/data/smap/data
Precipitation: CHIRPS (historical) https://www.chc.ucsb.edu/data/chirps
Precipitation Forecast: CHIRPS-GEFS https://chc.ucsb.edu/data/chirps-gefs