Sayed-Hossein Sadeghi

Sensitivity analysis of monthly reference crop evapotranspiration trends in Iran: a qualitative approach

The main objective of this study was to analyze the sensitivity of the monthly reference crop evapotranspiration (ETo) trends to key climatic factors (minimum and maximum air temperature (Tmax and Tmin), relative humidity (RH), sunshine hours (tsun), and wind speed (U2)) in Iran by applying a qualitative detrended method, rather than the historical mathematical approach. Meteorological data for the period of 1963–2007 from five synoptic stations with different climatic characteristics, including Mashhad (mountains), Tabriz (mountains), Tehran (semi-desert), Anzali (coastal wet), and Shiraz (semi-mountains) were used to address this objective. The Mann–Kendall test was employed to assess the trends of ETo and the climatic variables. The results indicated a significant increasing trend of the monthly ETo for Mashhad and Tabriz for most part of the year while the opposite conclusion was drawn for Tehran, Anzali, and Shiraz. Based on the detrended method, RH and U2 were the two main variables enhancing the negative ETo trends in Tehran and Anzali stations whereas U2 and temperature were responsible for this observation in Shiraz. On the other hand, the main meteorological variables affecting the significant positive trend of ETo were RH and tsun in Tabriz and Tmin, RH, and U2 in Mashhad. Although a relative agreement was observed in terms of identifying one of the first two key climatic variables affecting the ETo trend, the qualitative and the quantitative sensitivity analysis solutions did never coincide. Further research is needed to evaluate this interesting finding for other geographic locations, and also to search for the major causes of this discrepancy.

Modified G and GAVG Correction Factors for Laterals with Multiple Outlets and Outflow

Anwar’s friction correction factor, G, and the average correction factor, GAVG, are used to compute the head loss resulting from friction and to calculate the required inlet pressure in horizontal tapered sprinkler laterals with multiple outlets. As a result of their being developed by using a discrete outflow model, which consists of a finite number of operating outlets, the previous approaches for determining these factors required tables or the solving of relatively complex formulas that may be cumbersome. In addition, use of these factors is subject to certain errors when the Darcy-Weisbach equation is used because they are developed assuming a constant friction factor along the lateral. In this study, considering the continuous flow-rate variation concept, at first, two simple and direct equations for calculating the G and the GAVG factor were developed. The proposed equations are then adjusted for the case in which the variability of the friction factor should be considered. The validity of suggeste...

Design of Zero Slope Microirrigation Laterals: Effect of the Friction Factor Variation

AbstractMicroirrigation has become quite a common practice in agricultural production in various parts of the world. To achieve the optimum (hydraulic and economic) system performance, designers are often faced with the problem of designing a maximum lateral length which results in a desired coefficient of uniformity (CU) or an allowable pressure head variation (δH). Previous theoretical design approaches are usually based on a constant Darcy–Weisbach (DW) friction factor along the lateral and this assumption can lead to substantial errors. In the research reported in this paper, a new analytical design approach does not require the constant DW assumption for zero-slope laterals while it still takes into account the emitter exponent and the effect of minor friction losses caused by emitters. Assuming a constant friction factor along the lateral might result in errors up to 14% in the calculation of the maximum lateral length. Conversely, the maximum relative error caused by the application of the proposed...

Direct Calculation of Thermodynamic Wet-Bulb Temperature as a Function of Pressure and Elevation

A simple analytical method was developed for directly calculating the thermodynamic wet-bulb temperature from air temperature and the vapor pressure (or relative humidity) at elevations up to 4500 m above MSL was developed. This methodology was based on the fact that the wet-bulb temperature can be closely approximated by a second-order polynomial in both the positive and negative ranges in ambient air temperature. The method in this study builds upon this understanding and provides results for the negative range of air temperatures (2178 to 08C), so that the maximum observed error in this area is equal to or smaller than 20.178C. For temperatures

Closure to ‘‘Analytical Determination of Distribution Uniformity for Microirrigation Tapered Laterals Laid on Uphill and Horizontal Slopes’’ by Sayed Hossein Sadeghi and Troy Peters

08C, wet-bulb temperature accuracy was 60.658C, and larger errors correspondedto very high temperatures (Ta

Energy Grade Line Assessment for Tapered Microirrigation Laterals

398C) and/or very high or low relative humidities(5%,RH,10% or RH . 98%). The mean absolute error and the root-mean-square error were 0.158 and 0.28C, respectively.

Comparison of deficit irrigation management strategies on root, plant growth and biomass productivity of silage maize

Based on the mathematical procedure presented in the discussion, the discusser concludes that Eq. (13) [Eq. (7)] is only valid under a limited design case where y 1⁄4 1. He justifies this statement by denoting that it is only under this circumstance that Eq. (12) reduces to (13). In the following, we show that this conclusion is incorrect: 1. Basically our reference equation for evaluating Hav is Eq. (13) and not Eq. (12). Eq. (12) cannot be considered as an exact solution of Hav because it is derived by substituting the following approximation equation:

EVALUATION OF THE CHRISTIANSEN METHOD FOR CALCULATION OF FRICTION HEAD LOSS IN HORIZONTAL SPRINKLER LATERALS: EFFECT OF VARIABLE OUTFLOW IN OUTLETS

AbstractIn pressurized irrigation systems the total long-term costs can often be minimized by dividing the pipeline into segments of different diameters. To properly design such a system requires an accurate hydraulic analysis. In this study, an analytical procedure was developed to simulate the energy grade line along trickle laterals with dual pipe sizes. Appropriate equations were developed to accurately estimate several important design factors such as the total head loss (JTot), the total required head at the inlet (Ein) and the minimum pressure head along the lateral (Emin). The methodology takes into account the effect of the number of outlets along each reach of the lateral, outflow nonuniformity, friction factor variation, velocity head changes, and local losses. Friction losses were evaluated using the power form equation of the Darcy-Weisbach formula. Local losses and velocity head change were both addressed by obtaining an average along the lateral constant coefficient which is a function of t...