Why We Should Start Thinking About Soil Moisture

EarthzineEarth Observation, In-Depth, Original

Photo of dark soil and small mushroom

What is the importance of the moisture beneath our feet- and we’re not talking about sweat? Earthzine offers a quick look at why soil moisture matters.

What is soil moisture?

Rarely do we start our day thinking, ‰ÛÏI wonder how much moisture is in the soil?‰Û Some of us are not sure what soil moisture is or why it is even important. Soil moisture is difficult to define because it is used differently in different disciplines.

Generally, soil moisture is the water occupying the pore spaces between soil particles. Although soil moisture is a small component of the hydrologic cycle, it plays a major role in understanding and predicting climatic patterns. Finally this January, NASA will launch their Soil Moisture Active Passive (SMAP) Mission, which will deliver global soil moisture measurements. The soil moisture data retrieved from SMAP will be used for several applications; including monitoring drought; assisting crop productivity; predicting floods; weather forecasting; and linking water, energy, and carbon cycles.

Soil Moisture Measurements Matter

Soil moisture measurements in agricultural settings provide important information for drought early warning. The upper 200 centimeters of soils is classified as the ‰ÛÏroot zone soil moisture‰Û and is important for describing the water that is available to plants. When drought occurs, there is a deficit amount of moisture in the root zone, and consequently crop productivity diminishes. Having continuous soil moisture measurements will lead to improved crop yield forecasting, and irrigation planning.

Soil moisture measurements also are important for predicting floods. By assessing how wet the soil is before a rainstorm, we can predict the potential for flooding to occur. If the soil is already oversaturated, at its maximum water-holding capacity, a rain event will not be absorbed adequately through the soil and flooding will likely occur.

Currently, weather prediction relies more heavily on observing the moisture levels in the atmosphere, instead of observing the moisture levels of soils; yet this is mostly due to the lack of soil moisture data available. Having soil moisture measurements may provide for a more accurate weather forecast. For example, soil moisture measurements could provide meteorologists with information on the amount of water available to evaporate from the land surfaces, which is directly related to weather and climate forecasting.

Soil moisture links together the water, energy, and carbon exchanges between the land and the atmosphere. Observing soil moisture measurements allows for an assessment of the entire Earth system, and analyzing global changes is extremely important for understanding future climate change impacts.

SMAP Remote Sensing of Soil Moisture

SMAPåÊuses active and passive remote sensing instruments to measure soil moisture everywhere on the globe. The active radar observations deliver high spatial resolution with lower soil moisture sensitivity, while the passive radiometer observations deliver higher soil moisture accuracy with lower spatial resolution. By combining these two methods of remote sensing, SMAP will achieve soil moisture maps with the highest accuracy and resolution available. Most importantly, the soil moisture data will be publicly available through two NASA-designated Earth science data centers, the Alaska Satellite Facility and the National Snow & Ice Data Center.