General Formula for Estimation of Monthly Mean Global Solar Radiation in Different Climates on the South and North Coasts of Iran

Using sunshine duration, cloud cover, relative humidity, average of maximum temperature, and ground albedo as the input of several radiation models, the monthly average daily solar radiation on horizontal surface in various coastal cities of the South (25.23∘ N) and the North (38.42∘ N) of Iran are estimated. Several radiation models are tested and further are revised by taking into consideration the effects of relative humidity, ground albedo, and Sun-Earth distance. Model validation is performed by using up to 13 years (1988–2000) of daily solar observations. Errors are calculated using MBE, MABE, MPE, and RMSE statistical criteria (see nomenclature) and further a general formula which estimates the global radiation in different climates of coastal regions is suggested. The proposed method shows a good agreement (less than 7% deviation) with the long-term pyranometric data. In comparison with other works done so far, the suggested method performs a higher degree of accuracy for those of two regions. The model results can be extended to other locations in coastal regions where solar data are not available

Mid-level synoptic analysis of flood-generating systems in South-west of Iran (case study: Dalaki watershed river basin)

Flood is known as one of the most distractive natural disaster worldwide. Therefore, its prediction is of great importance from the socio-economical point of view. Despite the great improvement in computational techniques and numerical weather prediction approaches, so far, in Iran, an acceptable flood prediction method has not yet been introduced. The main aim of this study is to recognize and classify the patterns of synoptic systems leading to torrential rainfalls in a watershed basin located in south-west of Iran. In this research, 20 major floods characterized by high rainfall intensities and severe damage were selected. The pattern, extension, and the direction of movement of the selected synoptic maps from surface to 500 hPa pressure levels were identified. Furthermore, the position of cyclones, anti-cyclones and mid-level trough lines were carefully tracked and classified into different groups. The results show that the major severe floods occurring in Dalaki watershed river basin are mainly influenced by strengthening of the center of Sudan heat low (SHL) and the coincidence moisture feeding by the Indian Ocean and Mediterranean Sea. It was found that simultaneous merging of the SHL system and Mediterranean frontal system would intensify the flood intensities over the basin. The mean positions of high pressures, low pressures, the Red Sea trough lines and 1015 hPa isobars of the major floods are also discussed

GEOGRAPHICAL FACTORS AFFECTING THE PRECIPITATION REGIME IN IRAN

This study compares the precipitation regime by using harmonic analysis during the last four decades (1965-2004).We used interpolated precipitation data from different weather stations distributed across Iran by applying 15x15 km spatial grids for the interpolated data. Data validations were employed by statistical tests. In this study three harmonies of precipitation variances were evaluated. Variability of precipitation regime was explored by using three-harmonic analysis method. In addition, the effect of geographical factors (altitude, latitude, longitude) affecting to the precipitation regime was verified. Analysis of the first harmonic method proved that the main precipitation regime in Iran occurs in winter season as result of large scale Mediterranean systems passing over Iran in the mentioned season. Moreover, the fluctuations of the seasonal precipitation regime were found to be different, so that in one region led to the appearance of the new regimes and in other region caused change or disappearance of the regimes. In all three harmonics, variances of precipitation were mainly a function of the geographical factors. This effect was more evident in the third harmonic, in such a way that the increases in latitudes (moving to northern region) caused higher precipitation variance. This means that precipitation regime in northern sites are more exposed to local factors and seasonal precipitation than those of southern sites. The results of this research can be used in land–use projects, environmental plans and water resources management