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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

NASA’s Short-term Prediction and Transition Center – Land Information System (SPoRT-LIS) provides high-resolution (about 3-km) gridded soil moisture products in real-time to support regional and local modeling and improve situational awareness. The 0–100 cm soil moisture percentile data has shown to be a utility for drought monitoring. The near-surface (0–10 cm) layer responds quickly to heavy precipitation and rapidly drying events. In deeper layers, soil moisture evolves more slowly and has demonstrated greater utility overall for drought monitoring purposes since drought evolves typically on timescales of weeks to years. Learn more.

This Blended Soil Moisture Product (5cm All Blend), developed by researchers at Ohio State University and the University of Illinois, is a high-resolution gridded soil moisture map derived from in situ, model-generated, and satellite data. The 5 cm All Blend is computed using a simple average to combine 5 cm interpolated in situ volumetric water content (VWC) percentiles, NLDAS Noah 0-10 cm VWC percentiles, and Soil Moisture Active Passive (SMAP) L3 enhanced VWC percentiles (~5 cm). To match the NLDAS output time step, the All Blend is generated daily with a 5-day delay. Learn more.

 

0–100 cm Soil Moisture Percentile

The color with the hex code #630f08 identifies:
< 2
The color with the hex code #da2d20 identifies:
2 – 5
The color with the hex code #de7a2e identifies:
5 – 10
The color with the hex code #f6b573 identifies:
10 – 20
The color with the hex code #c8c8c8 identifies:
30 – 70

The color with the hex code #c3f7b2 identifies:
70 – 80
The color with the hex code #78f573 identifies:
80 – 90
The color with the hex code #37d23c identifies:
90 – 95
The color with the hex code #0fa00f identifies:
95 – 98
The color with the hex code #3c83e8 identifies:
> 98

5 cm Soil Moisture Percentiles

The color with the hex code #730000 identifies:
< 2
The color with the hex code #e60000 identifies:
2 – 5
The color with the hex code #e69800 identifies:
5 – 10
The color with the hex code #fed37f identifies:
10 – 20
The color with the hex code #fefe00 identifies:
20 – 30

The color with the hex code #aaf596 identifies:
70 – 80
The color with the hex code #4ce600 identifies:
80 – 90
The color with the hex code #38a800 identifies:
90 – 95
The color with the hex code #145a00 identifies:
95 – 98
The color with the hex code #002673 identifies:
> 98

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