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The validation of the variables (evaporation and soil water) in hydrometeorological models: Phase II, application of cosmic ray probes for soil water measurement
Expanded Title: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 (RS) products are becoming more widely used in hydrological modelling. However, RS 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. 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. One of the major challenges facing providers of SW products is validation. This project was initiated to provide a spatially explicit validation procedure for the 1 km grid of SW and ET produced by the SAHG at UKZN and other Global Climate models. The recent development of the Cosmic Ray Probes (CRP) was timely and provided a technology previously unobtainable, which fitted perfectly with the spatial resolution of this project. The CRP is a new and innovative in-situ instrument, capable of measuring SW at an intermediate scale. The CRP estimates were used to validate modelled SW estimates and the back-calculation of SW l from relative evaporation estimated from the SEBS Model.The back-calculation of SW from relative evaporation and evaporative fraction, estimated using the SEBS model, looked like a promising technique. The spatial resolution was less than the catchment area and the measurement depth was representative of the root zone of the vegetation (0.50 m). Therefore, this product would have the least horizontal and vertical scaling issues, when validated against the CRP. Although the back-calculation method results in SW estimates on a 30m spatial grid, the temporal resolution of the imagery used is 16 days and performed poorly against the CRP validation data. It is recommended that further research is required into the measurement of SW from RS products and the CRP.
Date Published:01/07/2017
Document Type:Research Report
Document Subjects:Water Resource Management/IWRM - Catchment Management
Document Keywords:Hydrology
Document Format:Report
Document File Type:pdf
Research Report Type:Standard
WRC Report No:2323/1/17
ISBN No:978-1-4312-0900-2
Authors:Everson CS; Mengistu MG; Vather T
Project No:K5/2323
Originator:WRC
Organizations:National Reseach Foundation; SAEON; University of Kwazulu Natal
Document Size:5 860 KB
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