Measuring Soil Moisture Contributes to Predicting Drought Impacts

Hurricanes, tornadoes and floods can be sudden and violent, causing a massive amount of damage. Drought, although less dramatic, is longer lasting, causes even more damage and has similar costs over a long period. Montana suffered a long drought from 1997 to 2006. The effects of this drought and more recent shorter duration droughts have had an enormous impact on the state of Montana, its farmers and ranchers, and the overall economy.

Measuring soil moisture contributes to predicting drought impacts

Stillwater County was hit hard. At the beginning of the drought, the Stillwater County Drought Advisory Board was asked what could be done to help. Their response was disaster declarations which mainly considered rainfall, streamflow, and storage, but did not accurately reflect drought conditions because effective soil moisture was not being measured. This input led to the installation of soil moisture sensors to provide information to help make better drought disaster determinations. Stillwater County joined other drought-stricken counties in 2002, and the Montana Counties Soil Climate Network (MCSCN) was formed. Over 60 stations were installed across the state and data made accessible. However, this effort was not sustainable due to lack of a statewide system for maintenance and support. Most of the stations are now defunct or inoperable.

A new local program was initiated by Stillwater County MSU Extension with support of the MSU Extension Climate Science team. Ten stations with improved, updated technology, measuring current weather conditions, as well as soil moisture and temperature at four depths, have been installed in Stillwater and four surrounding counties. These were made possible by collaborations with county commissioners, Extension agents, conservation

districts, local landowners, a Western Sustainable Agriculture Research and Education (WSARE) Grant and the Montana Mesonet.

While perseverance at the local level has been important, the project would not have been possible or sustainable without the Montana Mesonet. Stillwater County was excited to join the recently formed Montana Mesonet, a cooperative, statewide soil moisture and meteorological information network, coordinated by the Montana Climate Office (http://climate.umt.edu/mesonet/default.php ) that originated with the Montana Research and Economic Development Initiative. The Mesonet has formed partnerships with the Institute on Ecosystems, Bureau of Land Management, Montana Department of Agriculture, MSU Extension, MSU Agricultural Experiment Stations, Montana Bureau of Mines and Geology, Montana Department of Natural Resources and Conservation, National Oceanic and Atmospheric Administration (NOAA), and other watershed groups. These partnerships will ensure the sustainability and expansion of the 56 monitoring stations currently installed across the state.

During the next few years, the Montana Climate Office will be developing user-guided applications and web-interface tools that use soil moisture and weather information to help farmers, ranchers, and other resource managers make critical decisions. In fact, Montana’s first early drought warning tool that integrates sensor outputs and site-specific soil moisture measurements was released in November 2018 (http://climate.umt.edu/mesonet/). This monitoring system will provide reliable information on remaining reserves of plant-available water, enabling resource managers to adapt management strategies. Knowing early that plant-available water is approaching critical minimum values, ranchers could make early arrangements to purchase hay or move or sell cattle early, when prices are more favorable. Further, government agencies can gain a clearer picture of drought effects in the state to target relief efforts more effectively and refine maps to determine drought status. Any efficiency increase from more accurate weather and soil moisture information can translate into several million dollars in statewide savings each year.

Today it is much more widely-accepted that cumulative rainfall data alone is a poor predictor

of drought impact and that short-term soil moisture deficits can occur in years of average or above average rainfall. This has led to the following research on practical uses of soil moisture data.

Measuring soil moisture using satellites is being researched. Microwave observations from NASA’s Soil Moisture Active Passive Mission (SMAP) provides statewide remotely-sensed soil moisture information. The technology works on the principle that moisture in the soil changes how much incident microwave energy is reflected from Earth’s surface. Lucas Jones at University of Montana and SMAP detected the development of extreme soil moisture deficits and vegetation impacts during the 2017 Flash Drought, proving the system’s ability to provide early warning of emerging drought. Actual measurements from Montana Mesonet stations help ground the accuracy of the satellite system measurements.

Precision agriculture monitoring technologies including harvest yield and protein sensors, coupled with other remote sensing and geographic information, allow assessment of crop performance relative to fertilizer chemical and moisture inputs across all parts of a field. In addition, this information can be used to develop field-specific yield and protein predictive models. These models can help determine what inputs should be applied to the field when weather information is added as the primary variable. Soil moisture relates most closely to crop performance, hence the need for Mesonet soilmoisture measurements in the field where the other measurements are made and crop predictive models are developed. This research can be found at https:// sites.google.com/site/ofpeframework/home.

Forest species occurrence and productivity are determined on the majority of northern Rockies sites by water balance (a function of precipitation, site water storage capacity, and evaporative demand). Water balance is essential for developing appropriate forest management practices that maintain positive soil moisture, and for predicting stand and forest risks related to water deficits, such as insect outbreaks, severe wildfire impacts, forest productivity and carbon sequestration. More information can be found at http://forestry.msuextension.org/

Soil water-holding capacity interacts with cropping system management and weather patterns to determine rates of deep percolation through cultivated soils. In annual cultivation systems, deep percolation transports minerals like nitrate out of the root zone, resulting in losses of soil fertility resources while simultaneously compromising groundwater quality. Current modeling efforts quantify the interaction of weather, management and soils to determine deep percolation and leaching rates in a context that can inform management decisions to increase agricultural sustainability. These modeling efforts rely on soil moisture for calibration and are potentially broadly applicable in locations where soil moisture data is available. More information can be found at http://waterquality.montana.edu/

As these and other tools continue to be developed, feedback is sought. Please contact MSU Extension in Stillwater County (http://stillwater.msuextension. org/) with questions or to help test these tools to make sure they are useful to farmers, ranchers and those who manage the land. �

Montana Mesonet

by Lee Schmelzer MSU Extension Agent in Stillwater County