Decades of drought in the southwestern United States have led some scientists to classify the intense and prolonged drought as a “mega-drought.” But drought in North America took a different form in 2021, affecting areas that don’t experience long-term or intense drought as often. The northern Great Plains have faced drought for months.
According to US and Canadian drought watchers, an “extreme” drought first set in in North Dakota and Manitoba in mid-March 2021. In summer, extreme and “exceptional” drought (the worst classification ) had spread to parts of Montana, Minnesota, Alberta and Saskatchewan. Recent autumn rains have mitigated the impact in some areas, but most soils remain parched.
Drought in the northern Great Plains can affect crop production, as well as fodder for livestock. When assessing drought and its potential to affect agriculture, scientists look at a wide range of indicators such as rainfall, temperature, evapotranspiration, and the amount of moisture in the soil.
“Earth observation data can tell us a lot about the environmental conditions that impact crop production early enough in the growing season, and of course throughout the season,” said Mary Mitkish, Deputy Director of NASA Harvest, an applied science program advancing the use of Earth observations for agriculture and food security. “By combining satellite data with weather and other data sets, we can monitor crop conditions in depth and anticipate expected impacts on production. “
One of these indicators, soil moisture, is shown on the map above. Specifically, the map shows soil moisture anomalies; i.e. how the water content in the top meter (3 feet) of the soil from October 1 to 12, 2021, compared to normal conditions for the time of year. This layer of soil, called the “root zone”, is the most relevant layer for agriculture. Too little water here can prevent seeds from germinating or stunt plant growth.
The measurements were derived from data collected by the Soil Moisture Active Passive (SMAP) mission, NASA’s first satellite dedicated to measuring soil water content. SMAP’s radiometer can detect water within the top 5 centimeters (2 inches) of the ground. Scientists use this surface layer data in a hydrologic model to estimate the amount of water present in the root zone.
The second map below shows the storage of shallow groundwater, as measured by the Gravity Recovery and Climate Experiment Follow On (GRACE-FO) satellites on October 11, 2021. Compared to water in the root zone, which can react relatively quickly to rainfall events, is a deeper resource, and replenishes slowly. This deeper water source is used for crop irrigation, drinking water and can supply waterways during times of drought.
The Canadian Drought Monitor reported that at the end of September, 67 percent of Alberta was experiencing moderate to severe drought, including 97 percent of the province’s farmland. Sixty-four percent of Saskatchewan and 43 percent of Manitoba was experiencing moderate to exceptional drought, covering 100 percent of farmland in both provinces. High temperatures and a lack of rain throughout the summer led to low crop yields, especially wheat. The reduction in livestock feed has led some ranchers on the Canadian prairies to reform their herds.
In the United States, drought throughout the summer has also hit hard the growing areas of spring wheat, which is harvested from late summer to early fall. USDA harvest reports indicate that in mid-August, around the most critical time for spring wheat, harvest conditions were mostly fair to very poor in the Dakotas, the Montana and Minnesota.
Soils in parts of Iowa and Wisconsin also appeared unusually dry. However, in early fall, the condition of the corn crop was generally good to fair.
It remains to be seen how the current drought will affect the yields of winter wheat, which is sown in the fall and harvested in the spring. In early fall, nearly half of the winter wheat crops grown in the United States were still facing drought.
Images from NASA’s Earth Observatory by Lauren Dauphin, using soil moisture data courtesy of JPL and the SMAP science team and GRACE data from the National Drought Mitigation Center. Article by Kathryn Hansen with information provided by Mary Mitkish, Keelin Haynes and Estefania Puricelli / NASA Harvest. NASA Harvest is an applied science program whose mission is to enable and advance the adoption of satellite Earth observations by public and private organizations for the benefit of food security, agriculture and human resilience. and environmental in the United States and around the world. This consortium of scientists and agricultural stakeholders is led by the University of Maryland.