Cosmic-ray Soil Moisture Probe: A New Technology to Manage African Dryland Ecosystems

摘要

An estimated 200 million rural smallholders practice livestock-based or mixed livestock-crop-based agriculture in sub-Saharan Africa, where levels of poverty and food insecurity are among the highest in the world. Demographic, environmental, and climate changes have led to diminishing supply of resources that is crippling dryland productivity and increasing people's vulnerability. There is a need for research to develop, monitor, and evaluate strategies to cope with diminishing resource availabilityand build resilient ecosystems. Reliable, long-term measurements of soil moisture are critically needed for addressing productivity and food security in African drylands. We propose that measurements of effective infiltration, plant available water and deep drainage are sufficient metrics to understand dryland ecosystem health and to assess and evaluate restoration strategies. In this work, we evaluate the advantages and disadvantages of two different measurement methods, the cosmic-ray neutron method (as implemented in the COsmic-ray Soil Moisture Observing System (COSMOS) and eddy covariance techniques, for long-term measurements of African dryland water balance. We compare estimates of ecosystem level daily evapotranspiration between the two methodsover a six-month period at a site in central Kenya, and found the cosmic-ray method to be more appropriate. The eddy covariance data are smoother than the cosmic-ray measurements. However, the cosmic-ray neutron probe method provides additional information on the key variable, area-average soil moisture, allowing us to partition rainwater into infiltration, runoff, evapotranspiration, and deep drainage. In addition, cosmic-ray neutron probes are easier to operate and maintain, more robust and less expensive than eddy covariance towers, making them more appropriate for long-term deployments.