PI: Colin Everson (University of KwaZulu-Natal)
U.S. Partner: Marek Zreda (University of Arizona)
Project Dates: August 2013 to February 2017
Dr. Colin Everson (right) and a student with the cosmic ray probe at the Baynesfield Estate in KwaZulu-Natal (Photo courtesy Dr. Everson).
This PEER Science project leverages the recent development of the Cosmic Ray Probe (CRP) as part of a National Science Foundation-supported project. The CRP uses cosmic-ray neutrons to measure soil moisture content over an area of tens of hectares. Dr. Colin Everson and his research team will test the suitability of a cosmic ray moisture probe in providing data for the continued support of soil moisture modeling of South Africa using a hydrologically consistent land surface model, accurate field and satellite-scale estimates of soil moisture for the calibration of hydrometeorogical models, and estimation of the spatial variability of soil moisture at catchment scale.
The researchers plan to build capacity in South Africa by developing a network to extend the cosmic ray moisture probes to multiple applications. Measurements using the probe at area scales of up to 34 hectares have the potential to provide hydrometeorologists with an entirely new way of evaluating surface soil water at spatial scales never achieved with ground-based techniques. This will provide water resource managers, engineers, and agriculturalists with an invaluable but economical new tool to monitor the critical interface between the ground and atmosphere. This new technology can be employed in water demand forecasting and promises to improve the utilization of irrigation water, especially in water scarce regions like South Africa. The probe can also be used for predictive weather and climate models by measuring soil water content. This is currently a major source of uncertainty in weather and climate forecasts, due largely to a lack of suitable observations. The project should also improve the quality of soil moisture data that feed into the South African Flash Flood Guidance System, which provides alerts to the public based on current and predicted rainfall. The system currently uses a relatively crude evaporation model. Therefore, the application of CRP data should help in validating evaporation estimates with better temporal and spatial resolution, thus improving the accuracy of flash flood predictions.
Summary of Recent Activities
This PEER project leverages the recent development of the Cosmic Ray Probe (CRP) which uses cosmic-ray neutrons to measure soil moisture content over an area of tens of hectares. Dr. Colin Everson and his research team’s main objective was to test the suitability of a cosmic ray moisture probe in providing data for the continued support of soil moisture modeling of South Africa. They carried out this experiment using a hydrologically consistent land surface model, accurate field and satellite-scale estimates of soil moisture for the calibration of hydro-metrological models, and estimation of the spatial variability of soil moisture at catchment scale.
Understanding the spatial and temporal variability of total evaporation and soil water at different scales is of great importance in many land surface disciplines, such as hydrology. Soil water is a key hydrological variable, as it impacts the water and energy balance at the land surface-atmosphere interface and is the main water source for natural vegetation and agriculture. The CRP is a new and innovative in-situ instrument that is capable of measuring soil water at an intermediate scale. The CRP, once properly calibrated, is suitable for providing spatial estimates of soil water.
The CRP estimates were used to validate modelled soil water estimates.
For many field and modelling applications, accurate estimates of Soil Water (SW) are required, but are often lacking. Modelled estimates of SW are often used without proper validation and the verification of the results is questionable. In addition, remotely sensed products are becoming more widely used in hydrological modelling. However, remotely sensed SW measurement is faced with the difficulty of,”seeing” below the soil surface and penetrating the aerial plant canopy layer. This still presents a major source of uncertainty in many hydrological applications where SW forms the interface between the atmosphere and the vadose zone and ultimately streamflow generation.
The vulnerability of South Africa to climate and environmental change is increasing as demands on resources continue to rise in conjunction with rapidly growing populations. Disaster management agencies will have to adapt to the increasing number of natural disasters, including droughts and floods. In addition, water resources management, crop modelling, and irrigation scheduling all require accurate, spatially distributed,
daily estimates of SW and total evaporation (ET) from catchment to national scale. This will only be feasible through remote sensing technologies and it is therefore essential to further the development and integration of space-based technologies within already existing national disaster management plans
The major highlight at the completion of the project was the validation of hydrometeorological models using the stationery cosmic ray probes (CRP) at Cathedral peak and Baynesfield and the implementation of the CRP Rover. This is a new technology worldwide and the application in this project represented the first time this technology has been applied in Africa. The CRP equipment acquired through this PEER project has also created a platform for a young PhD student (Thigesh Vather) to use it as the focus of his PhD studies. An annual report on these activities was submitted to the WRC in February 2017.
Dr. Everson and his team are currently collaborating with his US partner to advance the application of the Cosmic Ray technology using high-resolution neutron and soil moisture mapping. This innovative research to calibrate CRP probes on multiple measurements of neutrons at meter scale within the hectometre scale of the stationary CRP probe will represent a major advance in this relatively new technology. Through this NSF PEER award they have recently purchased a CRP Rover system. This has multiple applications in hydro-meteorological modelling of flood and drought forecasting, irrigation scheduling for food production, water sustainability and protection of wetlands. In addition, we are looking at the long-term monitoring of soil water for climate change studies in the pristine grasslands of the KwaZulu-Natal Drakensberg. The stationary probe and CRP Rover have provided a 34 ha footprint that we have found useful for remote sensing validation at this larger scale. However, this scale has also presented limitations as it is not always possible to find homogenous areas of crops and natural vegetation of this size. The ability to map soil water at a finer resolution will represent a major advance in their hydrological and agricultural research.