Papers by Mohammad ElNesr
Theoretical and Applied Climatology, 2018
As the temperature and the diurnal temperature range (DTR) influence our life in many fields like... more As the temperature and the diurnal temperature range (DTR) influence our life in many fields like agriculture and health, changes in either parameter may affect our current and future plans in such areas. This paper investigates the variability of temperature and DTR in the Levant and the Arabian Peninsula (172 stations in 12 countries) in different study periods of 10, 25, 40, 50, and 60 years. The data were tested for homogeneity using four standard tests, and we used the nonparametric statistics Mann-Kendall and Theil-Sen to calculate trend significance, direction, and magnitude in time series. Our results show a significant warming trend in 45-60% of the region with an average increase of 0.65, 0.43, and 0.30 °C/decade for the 25-, 40-, and 50-year study periods. The highest number of stations that have a significant increase in temperature occurs in spring and summer. On the other hand, decreasing DTR trends occur in about 31% of the region, mostly in the south of the Arabian Peninsula at 0.60 °C/decade. This work, additionally, provides an interactive online tool that shows the trends and temperature on zoomable maps, charts, and other visuals to station level. This tool could benefit researchers and strategic planners for the studied region. In many stations, we found that there are a significant increase in temperature and a decrease in DTR which reflect a severe change in the climate that should be considered in future planning. We recommend expanding this study to cover precipitation and other meteorological factors. Highlights • We have studied the trends of temperature (T) and diurnal temperature range (DTR) for the Arabian Peninsula, the Levant, and Iraq. • We used the nonparametric statistics Theil-Sen and Mann-Kendall and compared them to the normal linear slope. • We performed the study for five different periods (10-60 years) and compared the results. • For each of the T and DTR, we studied the trends for maximum, minimum, and average seasonal values over years. • We have provided an online visualization tool that shows the trends on maps, line charts, and fountain charts for the benefit of the readers of the journal. Electronic supplementary material The online version of this article (https://doi.
Computers and Electronics in Agriculture , 2019
This is the second part of the companion papers assessing HYDRUS simulations of drip irrigation. ... more This is the second part of the companion papers assessing HYDRUS simulations of drip irrigation. While the first part focused on surface drip simulations, this part focused on the subsurface simulations and how they differ from the surface simulations. We evaluated the effect of different domain geometries, emission element shapes, coordinate systems, emitter discharges, and soil textures on the accuracy and stability of the simulation. The results showed that all the 2D and 3D simulations were done with a mass balance error of less than 0.9%, in contrast to the surface 2D cases that have large error values. The flux-conductivity ratio for subsurface simulations does not have the same influence on the mass balance error as in the surface simulations. We found extreme differences in the simulation speeds that were attributed to the emitter's location (the subsurface is faster), the domain axes (axisymmetric is faster than Cartesian), soil texture (the lighter is faster), the elapsed time or stage (the redistribution is hugely faster than redistribution). For the 2D-3D comparisons, we found that the 2D domains mostly underestimate the 3D slices. Finally, we found that the flux profiles of the 2D domains perfectly match the flux profiles of the 3D domains, in contrast to the surface comparisons. Hence, we can use 2D simulations reliably for subsurface drip, but not for the surface drip.
Computers and Electronics in Agriculture , 2019
HYDRUS is a popular package for simulating water and solutes movement in variably-saturated porou... more HYDRUS is a popular package for simulating water and solutes movement in variably-saturated porous media. It is widely used by designers of drip irrigation systems to simulate the active wetting pattern. However, there are many design parameters of the domain and for the flux calculation; other than the acceptable simulations, some configurations might cause underestimation or over-estimation of the wetting pattern. Comparative assessments of the surface drip simulation parameters were performed. We evaluated the effect of different domain geo-metries, element shapes, coordinate systems, emitter discharges, and soil textures on the accuracy and stability of the simulation. The results showed that the 3D simulations are more successful and reliable than the 2D simulations in terms of mass balance error. For the 2D domains, the error increases as the texture goes finer, and for axisymmetric domains than the Cartesian ones. We found a relationship between the flux and the soil hydraulic conductivity that their quotient should not exceed 1.8 and 3.2 for axisymmetric and cartesian coordinates. Our outcomes show that the infiltration stage took more time than the redistribution stage because of the variation in water content that delays the convergence at infiltration. Additionally, we found that the range between the saturated and the residual water content of the soil causes instability of the simulation as it gets higher. The differences between 2D simulations and the equivalent 3D slices were highly dependent on the soil texture, the heavier the larger; and dependent on the simulation phase, where the redistribution phase has fewer differences than the infiltration phase. Finally, we have determined the best matching 2D flux profile to each 3D profile and revealed the source of variation between 2D and 3D profiles where it was mostly-affected by the emitter's location, the soil texture, and simulation phase. In part 2 of this paper, we expanded the study for subsurface drip simulations and showed the difference between the two systems' designs.
Friction head loss equations and friction correction factors were evaluated and compared to field... more Friction head loss equations and friction correction factors were evaluated and compared to field observations collected from thirty
center pivots with laterals made of PVCs. The friction head loss equations include Darcy-Weisbach (D-W), Hazen-Williams (H-W), and Scobey, in addition to a proposed equation valid for smooth and rough pipe types and for all turbulent flow types. The proposed equation was developed by combining the equations of D-W and H-W, along with the multiple nonlinear regression technique. The friction correction factors were computed by using the typical Christiansen, modified Christiansen, Anwar, and Alazba formulae. The evaluation has been based on statistical error techniques with observed values as a reference. With the combination of modified Christiansen, Anwar, and Alazba formulae, the results revealed that the magnitudes of friction head loss calculated by using the D-W, H-W, and proposed equations were in agreement with field observations. The root mean square deviation (RMSD) values ranged from 1.6 to 1.7 m. As expected, and when the typical Christiansen friction correction factor was used with the D-W, H-W, and proposed equations, the results showed poor agreement between observed and computed friction head loss values. This was clearly reflected by the high RMSD values that ranged from 5.4 to 5.9 m. On the other hand, agreement occurred between observed friction head loss values and those calculated by using the Scobey equation, invalid for PVC pipe type, when combined with the typical Christiansen formula. This interesting finding led to improved results of the Scobey equation through a developed Cs coefficient suitably valid for PVC pipe type through analytically mathematical derivation; accordingly, the RMSD value dropped from approximately 8.6 to 1.6 m.
Applied and Environmental Soil Science, 2013
Spanish Journal of Agricultural Research, 2015
Saxton Equations to determine field capacity, wilting point, saturated conductivity, porosity, an... more Saxton Equations to determine field capacity, wilting point, saturated conductivity, porosity, and bulk density from clay and sand percents. All in MS.Excel format. by Dr. Mohammd ElNesr Source: K.E. Saxton et al., 1986, Estimating generalized soil-water characteristics from texture. Soil Sci. Soc. Amer. J. 50(4):1031-1036
PLOS ONE, 2015
The effects of three water management techniques were evaluated on subsurface drip irrigated toma... more The effects of three water management techniques were evaluated on subsurface drip irrigated tomatoes. The three techniques were the intermittent flow (3 pulses), the dual-lateral drip system (two lateral lines per row, at 15 and 25 cm below soil surface), and the physical barrier (buried at 30 cm below soil surface). Field experiments were established for two successive seasons. Water movement in soil was monitored using continuously logging capacitance probes up to 60 cm depth. The results showed that the dual lateral technique positively increased the yield up to 50%, water use efficiency up to 54%, while the intermittent application improved some of the quality measures (fruit size, TSS, and Vitamin C), not the quantity of the yield that decreased in one season, and not affected in the other. The physical barrier has no significant effect on any of the important growth measures. The soil water patterns showed that the dual lateral method lead to uniform wetting pattern with depth up to 45 cm, the physical barrier appeared to increase lateral and upward water movement, while the intermittent application kept the wetting pattern at higher moisture level for longer time. The cost analysis showed also that the economic treatments were the dual lateral followed by the intermittent technique, while the physical barrier is not economical. The study recommends researching the effect of the dual lateral method on the root growth and performance. The intermittent application may be recommended to improve tomato quality but not quantity. The physical barrier is not recommended unless in high permeable soils.
Principles and Applications for Water Management, 2013
Principles and Applications for Water Management, 2013
IOSR Journal of Agriculture and Veterinary Science, 2014
Arabian Journal of Geosciences
Identifying the shortwave solar radiation, Rs, is very important in various fields of science whi... more Identifying the shortwave solar radiation, Rs, is very important in various fields of science which is calculated by mathematical models if not measured experimentally. These models depend on the coastality factor, kr. Several equations are developed to calculate kr but with errors of estimation. The aim of this paper was to develop a local formula to calculate kr from temperature range. Based on the 30-year climate data for 29 weather stations throughout the Kingdom of Saudi Arabia (KSA), monthly temperature ranges were calculated. The hyperbolic equation was derived based on the best-fit analysis and the resulted errors of four statistical parameters were compared with any other established formula. The average of the absolute percent error was estimated as 2.1% as compared with 6–11% of the various published models. Results show that kr is inversely proportional to the distance from the coast and the altitude. In addition, it was found that urbanization has a considerable effect on kr and the noncoastal but high-population cities behaved similar as coastal cities. It is recommended to use the proposed equation due to its accuracy for the KSA instead of using other models. More research is needed to further investigate the effects of urbanization on the kr.
The developed model 'Drip Chartist' by Ismail et al. (2006a) was verified and validated in field ... more The developed model 'Drip Chartist' by Ismail et al. (2006a) was verified and validated in field and by comparison to other related model "Hydrus 2D". Field validation resulted showed that the surface system without hydraulic barrier represents the real-condition by 94.99% (correlation coefficient of 0.9746) with under estimation of 0.157. While in the subsurface system with hydraulic barrier represents the realcondition by 81.96% (correlation coefficient of 0.9053) with under estimation of 0.021.
ABSTRACT A computer model was developed to simulate surface and subsurface drip irrigation system... more ABSTRACT A computer model was developed to simulate surface and subsurface drip irrigation systems. The model combines the alternate direction implicit method (ADI) of solving two dimensional linear partial differential equations with the iterative Newton-Raphson method to advance through variable time steps. After each time step, a volume balance is applied to avoid error accumulation. Several techniques were selected to harmonize the auxiliary equations in the model.
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Papers by Mohammad ElNesr
center pivots with laterals made of PVCs. The friction head loss equations include Darcy-Weisbach (D-W), Hazen-Williams (H-W), and Scobey, in addition to a proposed equation valid for smooth and rough pipe types and for all turbulent flow types. The proposed equation was developed by combining the equations of D-W and H-W, along with the multiple nonlinear regression technique. The friction correction factors were computed by using the typical Christiansen, modified Christiansen, Anwar, and Alazba formulae. The evaluation has been based on statistical error techniques with observed values as a reference. With the combination of modified Christiansen, Anwar, and Alazba formulae, the results revealed that the magnitudes of friction head loss calculated by using the D-W, H-W, and proposed equations were in agreement with field observations. The root mean square deviation (RMSD) values ranged from 1.6 to 1.7 m. As expected, and when the typical Christiansen friction correction factor was used with the D-W, H-W, and proposed equations, the results showed poor agreement between observed and computed friction head loss values. This was clearly reflected by the high RMSD values that ranged from 5.4 to 5.9 m. On the other hand, agreement occurred between observed friction head loss values and those calculated by using the Scobey equation, invalid for PVC pipe type, when combined with the typical Christiansen formula. This interesting finding led to improved results of the Scobey equation through a developed Cs coefficient suitably valid for PVC pipe type through analytically mathematical derivation; accordingly, the RMSD value dropped from approximately 8.6 to 1.6 m.
center pivots with laterals made of PVCs. The friction head loss equations include Darcy-Weisbach (D-W), Hazen-Williams (H-W), and Scobey, in addition to a proposed equation valid for smooth and rough pipe types and for all turbulent flow types. The proposed equation was developed by combining the equations of D-W and H-W, along with the multiple nonlinear regression technique. The friction correction factors were computed by using the typical Christiansen, modified Christiansen, Anwar, and Alazba formulae. The evaluation has been based on statistical error techniques with observed values as a reference. With the combination of modified Christiansen, Anwar, and Alazba formulae, the results revealed that the magnitudes of friction head loss calculated by using the D-W, H-W, and proposed equations were in agreement with field observations. The root mean square deviation (RMSD) values ranged from 1.6 to 1.7 m. As expected, and when the typical Christiansen friction correction factor was used with the D-W, H-W, and proposed equations, the results showed poor agreement between observed and computed friction head loss values. This was clearly reflected by the high RMSD values that ranged from 5.4 to 5.9 m. On the other hand, agreement occurred between observed friction head loss values and those calculated by using the Scobey equation, invalid for PVC pipe type, when combined with the typical Christiansen formula. This interesting finding led to improved results of the Scobey equation through a developed Cs coefficient suitably valid for PVC pipe type through analytically mathematical derivation; accordingly, the RMSD value dropped from approximately 8.6 to 1.6 m.