Opportunities and challenges in using soil moisture from cosmic ray neutron sensing for rainfall-runoff modelling

2021-9-08
Duygu, Mustafa Berk
Retrieving or estimating soil moisture is one of the most important elements of hydrology, since most of the hydrological studies consider the absence (drought) or excessiveness (flood) of water stored in the soil. Water stored in a basin has a very strong relation with the amount of soil moisture thus knowing the soil moisture significantly facilitates the estimation of other parameters of the hydrological cycle. For agricultural decision making systems, it is also vital to know whether the plants receive the amount of water necessary for their growth, which can be indicated by the amount of soil moisture. There are various ways of measuring soil moisture, where each technique has its own advantages and disadvantages. Some of these methods can provide very accurate measurements with very high costs or they may have very high temporal resolutions with limited spatial coverages. Among different methods, soil moisture measurement from recently invented Cosmic Ray Neutron Probes (CRNPs) has a good potential to be used in hydrological studies due to its larger spatial coverage, low cost and high temporal resolution. It is also possible to use this product together with satellite soil moisture products to obtain reliable soil moisture information with even more spatial coverage. The aim of this study is to assess the effectiveness of CRNPs in determination of soil moisture at basin scale, to validate satellite soil moisture products and to use the soil moisture information derived from CRNP and satellite products for improving hydrological modeling. For this study, the first CRNP of Turkey has been installed in Çakıt Basin, south of Turkey, and the neutron counts obtained from the CRNP have been converted into soil moisture values after a series of correction and conversion processes. The CRNP based soil moisture data have been used in the validation of different soil moisture satellite products to test the effectiveness of CRNPs in satellite product validation and assess the potential of using CRNPs in conjunction with satellite soil moisture products for studies covering relatively larger areas. The relation between soil moisture and evaporation is also investigated through CRNP soil moisture values. Finally, CRNP based soil moisture data have been introduced into the calibration of a conceptual hydrological model and it has been found that introducing CRNP soil moisture data into NAM conceptual model improves the model statistics of Çakıt Basin (421 km²) and one of its sub basins, Darboğaz sub-basin (121 km²). Using CRNP based soil moisture data to calibrate the NAM model increased the Kling-Gupta Efficiency score for the discharge data of Çakıt Basin from 0.56 (Calibration) and 0.42 (Validation) to 0.81 (Calibration) and 0.64 (Validation). Similar improvements were noted for most of the statistical measures for both Çakıt Basin and Darboğaz sub-basin.

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Citation Formats
M. B. Duygu, “Opportunities and challenges in using soil moisture from cosmic ray neutron sensing for rainfall-runoff modelling,” Ph.D. - Doctoral Program, Middle East Technical University, 2021.