July 2018 was the driest July in Australia since 2002. The dry month exacerbated an ongoing drought that had already ruined large swaths of grazing land and cropland. New South Wales has been hit the hardest, according to a news reports. About 99 percent of the state was in drought heading into August.

Drought becomes relevant to farmers and ranchers when there are deficits in the amount of water available to plants in the “root-zone,” which generally includes the top 200 centimeters (80 inches) of soil. The map above shows root-zone soil moisture anomalies—how much the moisture content was above (green) or below (brown) the norm—on July 28, 2018. Soils were extremely dry in eastern Australia, which is a major agricultural area.

“Agricultural drought can irreversibly damage crops and hamper yield formation, leading to economic losses and food insecurity,” said Iliana Mladenova, a scientist at NASA’s Goddard Space Flight Center.

The map is derived from data collected by the Soil Moisture Active Passive (SMAP) mission, the first NASA satellite dedicated to measuring the water content of soils. SMAP’s radiometer can detect the amount of water in the surface layer of the soil; that is, the top 5 centimeters (2 inches) of the ground. Scientists use that surface layer data in a hydrologic model to estimate how much water is present even deeper in the root zone. Analyzing this moisture can tell you whether there is enough water for plants to function properly and to achieve an optimal yield.

“Timely and accurate knowledge of the root-zone soil moisture is very important for farmers, stakeholders, and agricultural agencies,” Mladenova said. “Soil moisture provides the necessary information to track and monitor drought development and occurrence, and predict its impact on end-of-season yields.”

NASA Earth Observatory image Joshua Stevens, using soil moisture data from NASA-USDA and the SMAP Science Team. Story by Kathryn Hansen.