Drought monitoring: a system for tracking plant available soil moisture based on the Oklahoma Mesonet

Statement of critical regional or State water problem:
Real-time drought monitoring is essential for early detection and adaptive management to mitigate the negative impacts of drought on the people, economy, and ecosystems of Oklahoma, and improved drought monitoring is a key need identified in the 1995 Update of the Oklahoma Comprehensive Water Plan.  Drought impacts can be severe in Oklahoma.  For example, the 2006 drought cost the state's economy over $500 million from lost crop production alone. While drought monitoring is critical to Oklahoma's resource managers, it is hampered by a lack of data on a crucial drought indicator:  plant available water.  Crop yield losses and, by extension, the economic impacts of drought, are strongly linked to plant available water (i.e. the amount of soil moisture which is available for plant uptake).  Real-time monitoring of plant available water requires two components: (1) sensors which monitor soil moisture and (2) knowledge of the site-specific soil properties controlling the plant availability of soil moisture.  In Oklahoma, the first of these requirements is already met via the Oklahoma Mesonet, an automated network of 120 stations that collect real-time observations of soil and atmospheric variables across the state (Fig. 1). However, the component needed to monitor plant available water and dramatically improve drought monitoring across Oklahoma is increased knowledge of the soil properties at the Mesonet sites. 

Fig. 1.  The locations of the Oklahoma Mesonet stations

Nature, scope, and objectives of the project:
The long term goal of the team of collaborators representing Oklahoma State University, the Oklahoma Mesonet, the Oklahoma Climatological Survey, and the University of Oklahoma is to develop and implement a system for accurately monitoring soil moisture and plant available water at each Mesonet station and to predict those values in near real-time for all other locations across Oklahoma.  The objective of this proposal is to complete a critical first stage of the research and improve drought monitoring in Oklahoma through the development of a Mesonet-based system for tracking plant available water.  The central hypothesis of the proposed work is that measuring key soil properties at each Mesonet site will allow the proposal team to integrate the existing soil moisture data into an accurate measure of plant available water.  Preliminary data presented in this proposal provide early support for this hypothesis. The rationale for the proposed research is that providing resource managers with real-time data on plant available water will enable them to adopt management strategies (e.g. crop marketing contracts, cattle stocking rates, hay purchases, fertilizer rate adjustments) to mitigate drought impacts.  The proposal team is well prepared to succeed with this project due to the extensive expertise and strong achievement records in soil moisture related research, leadership in managing the Oklahoma Mesonet, and experience in the development of online products through the popular websites www.mesonet.org and www.agweather.mesonet.org.  The following specific aims are proposed as part of the project:

Specific aim #1:  Determine the soil properties controlling the plant availability of soil moisture at each Mesonet site.  Soil samples will be collected from every site and key soil physical properties will be measured in the laboratory.

Specific aim #2:  Develop a routine to calculate plant available water by integrating the sensor output and the site-specific soil properties. Existing pedotransfer functions will be used together with the measured soil properties to translate the output from the sensors (Campbell Scientific, Model 229, heat dissipation sensors) into prototype plant available water maps.

Statement of results or benefits:
The proposed project is a truly unique research opportunity because no other state in the nation and no other region in the world has a soil moisture sensing infrastructure comparable to that of the Oklahoma Mesonet.  At the completion of this project, it is expected that an innovative drought monitoring system, providing resource managers with reliable, daily updated information on the remaining reserves of plant available water, has been developed and coupled with the unmatched resources of the Oklahoma Mesonet.  This system and the products developed will enable end users to more effectively adapt their management strategies.  For example, by knowing early that plant available water is decreasing and reaching critical minimum values, farmers could reduce mid-season N fertilizer application rates on wheat, change forward contracting strategies, or choose to graze out more wheat.  Similarly, ranchers, facing the potential for reduced pasture, could make early arrangements to purchase hay or could sell cattle early, when prices are more favorable.  Further, government agencies, such as the Oklahoma Water Resources Board, could gain a clearer picture of the extent of drought effects in the state and could target relief efforts more effectively.