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Soil Moisture

Soil moisture plays an important role in agricultural monitoring, drought and flood forecasting, forest fire prediction, water supply management, and other natural resource activities. Soil moisture observations can forewarn of impending drought or flood conditions before other more standard indicators are triggered.

What Is Soil Moisture?

A young plant growing in soil

As defined by the AMS Glossary of Meteorology, soil moisture is “the total amount of water, including the water vapor, in an unsaturated soil.” Soil moisture—sometimes also called soil water—represents the water in land surfaces that is not in rivers, lakes, or groundwater, but instead resides in the pores of the soil. The level of soil moisture is determined by a host of factors beyond weather conditions, including soil type and associated vegetation. In turn, soil moisture levels affect a range of soil and plant dynamics. Surface soil moisture is the water that is in the upper 10 cm of soil, whereas root zone soil moisture is the water that is available to plants—generally considered to be in the upper 200 cm of soil.

 

Data, Maps, and Tools

The amount of soil moisture can have significantly different implications depending on location, season, soil type, and depth. For example, the same absolute value of soil moisture can indicate a serious drought in the Southeast, while it represents normal soils in the Southwest. Interpreting soil moisture data requires assessing and maintaining a range of other “metadata,” particularly soil characteristics. It also means that more than one unit of measure may be needed to adequately describe conditions, including not only “volumetric water” (the volume of water present), but also anomalies, daily ranking percentages, etc.

The techniques for monitoring soil moisture are undergoing rapid growth and innovation with the advent of new in situ and proximal sensors, new satellite and other remote sensing technologies, and enhanced modeling capabilities. This is leading to an increasing number of soil moisture data products in development.

Current Soil Moisture Conditions

0–100 cm Soil Moisture Percentile
Range Map Hex Color Description
0 - 2 #630f08 0–2nd Percentile Soil moisture at 0–100cm depth is in the bottom 2% (0–2nd percentile) of historical measurements for this day of the year. Learn more.
2 - 5 #da2d20 2nd–5th Percentile Soil moisture at 0–100cm depth falls between the 2nd to 5th percentile of historical measurements for this day of the year. Learn more.
5 - 10 #de7a2e 5th–10th Percentile Soil moisture at 0–100cm depth falls between the 5th to 10th percentile of historical measurements for this day of the year. Learn more.
10 - 20 #f6b573 10th–20th Percentile Soil moisture at 0–100cm depth falls between the 10th to 20th percentile of historical measurements for this day of the year. Learn more.
20 - 30 #ffff66 20th–30th Percentile Soil moisture at 0–100cm depth falls between the 20th to 30th percentile of historical measurements for this day of the year. Learn more.
30 - 70 #c8c8c8 30th–70th Percentile Soil moisture at 0–100cm depth falls between the 30th to 70th percentile of historical measurements for this day of the year. Learn more.
Range Map Hex Color Description
70 - 80 #c3f7b2 70th–80th Percentile Soil moisture at 0–100cm depth falls between the 70th to 80th percentile of historical measurements for this day of the year. Learn more.
80 - 90 #78f573 80th–90th Percentile Soil moisture at 0–100cm depth falls between the 80th to 90th percentile of historical measurements for this day of the year. Learn more.
90 - 95 #37d23c 90th–95th Percentile Soil moisture at 0–100cm depth falls between the 90th to 95th percentile of historical measurements for this day of the year. Learn more.
95 - 98 #0fa00f 95th–98th Percentile Soil moisture at 0–100cm depth falls between the 95th to 98th percentile of historical measurements for this day of the year. Learn more.
98 - 100 #3c83e8 98th–100th Percentile Soil moisture at 0–100cm depth is in the top 2% (98th to 100th percentile) of historical measurements for this day of the year. Learn more.
20 cm Soil Moisture Percentile
Range Map Hex Color Description
0 - 2 #730000 0–2nd Percentile Soil moisture at 20cm depth is in the bottom 2% (0–2nd percentile) of historical measurements for this day of the year. 
2 - 5 #e60000 2nd–5th Percentile Soil moisture at 20cm depth falls between the 2nd to 5th percentile of historical measurements for this day of the year.
5 - 10 #e69800 5th–10th Percentile Soil moisture at 20cm depth falls between the 5th to 10th percentile of historical measurements for this day of the year. 
10 - 20 #fed37f 10th–20th Percentile Soil moisture at 20cm depth falls between the 10th to 20th percentile of historical measurements for this day of the year.
20 - 30 #fefe00 20th–30th Percentile Soil moisture at 20cm depth falls between the 20th to 30th percentile of historical measurements for this day of the year.
30 - 70 #c8c8c8 30th–70th Percentile Soil moisture at 20cm depth falls between the 30th to 70th percentile of historical measurements for this day of the year.
Range Map Hex Color Description
70 - 80 #aaf596 70th–80th Percentile Soil moisture at 20cm depth falls between the 70th to 80th percentile of historical measurements for this day of the year. 
80 - 90 #4ce600 80th–90th Percentile Soil moisture at 20cm depth falls between the 80th to 90th percentile of historical measurements for this day of the year.
90 - 95 #38a800 90th–95th Percentile Soil moisture at 20cm depth falls between the 90th to 95th percentile of historical measurements for this day of the year. 
95 - 98 #145a00 95th–98th Percentile Soil moisture at 20cm depth falls between the 95th to 98th percentile of historical measurements for this day of the year. 
98 - 100 #002673 98th–100th Percentile Soil moisture at 20cm depth is in the top 2% (98th to 100th percentile) of historical measurements for this day of the year. 
Root Zone Soil Moisture: Wetness Percentile
Range Map Hex Color
0 - 2 #730000
2 - 5 #E60000
5 - 10 #FFAA00
10 - 20 #FCD37F
20 - 30 #FFFF00
30 - 70 #ffffff
Range Map Hex Color
30 - 70 #ffffff
70 - 80 #8ccdef
80 - 90 #99BFFF
90 - 95 #1D90FF
95 - 98 #4169E1
98 - 100 #0000FF

Related Content

By Sector | Agriculture

Agricultural drought occurs when drought conditions negatively affect crops and forage. Learn more about how drought affects the agriculture sector.

Research & Learn | Flash Drought

In its simplest form, flash drought is generally considered the rapid onset of drought, which can cause extensive, unexpected damage to agriculture and economies. Changes in soil moisture can provide an early warning of flash drought. 

Research and Learn

Balancing the Water Budget: Advancements in Soil Moisture Monitoring and Interpretation

Soil moisture is a vital part of the Earth’s water budget, yet given the complexities in measuring and interpreting soil moisture, an accurate depiction of this variable has been a serious challenge over the past several decades. This means that important public needs, such as drought and flood early warning, water management, and agricultural monitoring, are not being fully addressed.

To address this situation, NIDIS is working with USDA and other partners to develop a strategy for a National Coordinated Soil Moisture Monitoring Network (NCSMMN). The goals of this initiative include:

  • Establishing a national “network of networks” that effectively demonstrates data and operational coordination of in situ networks and addresses gaps in coverage
  • Supporting R&D on innovative techniques to merge in situ soil moisture data with remotely-sensed and modeled hydrologic data to create near-real time, gridded, user-friendly soil moisture maps and associated tools
  • Building a community of practice and expertise around soil moisture measurement and interpretation.
Soil probes seen from above

Soil Moisture Research and Resources