نشریه نیوار
پیاپی 90-91 (پاییز و زمستان 1394)

The analysis of frequency and return period of rainfall and flood events is the most important step in water resources management and hydraulic structure designing. In this paper¡ the data of 24-hour maximum precipitation in five synoptic stations of Tehran province were provided to identify the best-fit distribution. Then¡ the results of nine probability distributions including Normal (N)¡ 2-parameter log-normal (LN2)¡ 3-parameter log-normal (LN3)¡ Pearson type 3 (P3)¡ Log-Pearson type 3 (LP3)¡ Gumbel (GUM)¡ Generalized extreme values (GEV)¡ Generalized logistic (GLOG)¡ Generalized Pareto (GPA) distributions were compared with the partial series fitted to exponential distribution using HYFA and MATLAB softwares. The RMSE ¡R2 ¡Bias ¡MAE and (Relative Root Mean Square Error) RRMSE statistics were used to identify the best-fit distribution at all stations. The results showed GPA at Abali and Mehrabad stations¡ GLOG at Doshantapeh and Northern Tehran stations and LN3 at Karaj station have better fit to data. Also¡ the Normal Exponential distributions were the most unsuitable ones. Finally¡ the results of RRMSE statistic represented that GEV distribution is the best-fit distribution and can be suggested for analyzing of maximum daily rainfall for the study area.

Mesoscale weatherforecast model(WRF) has a wide variety of physical parameterizations schemes and choosing a particular set of schemes can have a significant impact on the accuracy of model predictions. So according to weather systems we should select an appropriate options of these schemes. In this study¡ accuracy of 24 hours predictions in the south west of Iran post processed from December 2011 until February 2012 with 9 different WRF configurations has been considered. Post processing is done by 2×2 contingency table. Despite great difficulties in precipitation prediction¡ post processing of the bias quantity shows that WRF model overestimates forecast for all precipitation thresholds for all configurations except for 10-15 mm rainfalls thresholds for the 3rd configuration and over 15 mm rainfalls thresholds for the 2nd and3rd configurations that have underestimated the forecast. Proportion correct quantity (PC) for under and over 15 mm rainfalls shows respectively the 3rd and 2nd configurations are good by 91 and 97 percent accuracy. Comparing the bias quantity(B) for 9 configurations in 4 rainfalls thresholds indicates that the model has overestimated the forecast for the mild and moderate rains¡ severe rains except the 3rd configuration and heavy rains except the 2nd and 3rd configurations. This quantity shows that the 3rd configuration for mild to severe rainfalls and the 4th configuration for heavy precipitation are more appropriate. For the hit rate quantity (H)¡ the 2nd configuration for mild to mean rainfalls¡ the 4th configuration for severe rains and the 8th configuration for heavy precipitations¡ are more appropriate. Pierce skill scores (PSS) shows that for rainfalls thresholds below 10 mm the 2nd configuration is good. This score appropriates the 4th configuration for thresholds rainfalls between 10-15 mm and the 8th configuration for thresholds rainfalls over than 15 mm. Generally for light precipitations (0.1-5 mm) and moderate rainfalls (5-10 mm)¡ the 2nd and 3rd configurations have higher accuracy among the others. For severe precipitations (10-15 mm) the 3rd and 4th configurations have higher accuracy compared to the others. However¡ in the case of heavy rainfalls (more than 15 mm) the 2nd and 3rd configurations have similar results and a specify configuration can not be chosen between them.

The aim of this study was to investigate temporal and spatial distribution of beginning and ending of frost at the base and future period in the northern region of the country. For this goal¡ the minimum temperature data of several synoptic stations in the study area including Bandar Anzali¡ Rasht¡ Gorgan¡ Ramsar¡ Nowshahr and Babolsar have been used. In this research¡ the period 1976-2005 and 2012-2039 is considered as the base and the future period¡ respectively. It is noted that the data of ECHO-G model have been used for determining of beginning and ending of frost in the daily scale. In this paper¡ we have used from ARC GIS software for mapping of beginning and ending of frost. The obtained results show that the beginning date of frost is a function of latitude and follow up of Eastward arrangement. In other words¡ with moving from West to East¡ beginning of frost comes sooner. The results suggest that future frost will start earlier and will end sooner. Namely¡ the beginning date of frost will move from early winter to late autumn. The results indicated that the beginning date of frost in the eastern region in the coming period (29 November) will occur about 10 days earlier than last period (19 November). This value is lower in the western regions and will reach from 12 January to 7 January in the coming period. In central and southern parts of the study area¡ the frost will occur seven days earlier and will be reached from 26 December to 19 December. The results also show that in most areas studied¡ ending date of frost will take place 0-23 days earlier than last year and in compared with the last period (7 March)¡ it will occur on 12 February. So¡ the growing season length in northern regions will increase in future periods. The maximum number of frost days associated with East coast and West coast has the lowest number of frost days. .

In this study¡ daily rainfall data of 95 synoptic stations of the country were used in a 18-year statistical period (1990-2007) in order to determine spatial – temporal distribution and zoning severity of risk degree of rainfall event in road transport network of the country. In addition¡ Spline with Barrier Interpolation Method was also used in this study by Critical Threshold Indicators in Arc GIS environment (rainfall with severity of 30mm and more¡ rainfall exceeding 90 percent and coefficient of variability of daily rainfall). The results show that maximum risk degree of spatial distribution and frequency of severity of rainfall can be observed in west-part roads of the Caspian region and central and northwest part of mountainous region of the country. In the same direction¡ maximum frequency of threshold rainfall severity is related to the main roads of cities of Anzali (304 days)¡ Kuhrang (277 days) and Rasht (210 days). In the same direction¡ maximum risk of temporal distribution of rainfall severity is observed in January (In Day month especially in southwest regions of the country) and March (April month in west regions of the country) in monthly scale in main roads network. The maximum coefficient of rainfall changes is observed in southeast regions of the country and maximum rainfall share exceeding 90 percent of total annual rainfall in the country is seen in west region of the country and also in west part of northern region.

Time series analysis in mathematical modeling and prediction of future events is very important. The aim of this research is to analyze changes in temperature during the day and at night in the city of Kerman station¡ during different months of the 2010-1961 period. For this purpose¡ the Mann-Kendall test statistic Z (at 95 percent) is used. The results showed day time temperature in the months of November¡ December¡ January¡ February and April (cold period) has increased. Also¡ the temperature at night during the months of June¡ July¡ August and September (warm period) have decreased. This means that the days of the cold period during the last half century¡ have been warmer than normal (especially in the months of November¡ December¡ January¡ February and April). While the nights warm period¡ have been cooler than normal levels (especially in the months of June¡ July¡ August and September).

Climatic characteristics have a significant impact on the development of ecotourism in a region. In this regard it can be taken a major step forward in the growth and prosperity of the region by identifying effective parameters in tourism planning. In relation to tourism activity¡ what that help the development of this activitiy¡ is depends on Tourism Climate. In this research with method of descriptive- analytical in order to evaluation of tourism climate in Noor city for ecotourism development¡ climate parameters have been analyzed using models Beiker¡ TCI and Terjung. The results show that there is suitable climatic conditions for tourism in both the Terjung and TCI in the months of June¡ July¡ August and September but none of the months of the year is favorable climatic according to result of Beiker.

Analyzing temperature profile of the Earth''s atmosphere is an essential work for understanding the dynamic¡ radiative and chemical processes occur within the atmosphere and its boundary layers. Such analysis is also critical for the detection and modeling of climate change. Several studies is made on different temporal and spatial scales of the vertical structure of the atmosphere. Expanding knowledge and technology of remote sensing is also helpful to identify the vertical profile of the atmosphere. For better understanding the characteristics of vertical temperature profile in southern parts of Iran¡ daily records of radiosonde data at Shiraz station (Latitude 29.6N and Longitude 52.5E) were collected for the period 2005-2010. The dataset consisted of pressure¡ temperature and relative humidity data gathered from surface up to 30 Km above sea level at 0:0 Greenwich Mean Time GMT (3:30 am local time). Daily data were firstly transformed to monthly and seasonal time-series using arithmetic averaging procedure. There was no significant changes in pattern of vertical profiles of temperature fluctuations in the years studied. The study has found a temperature inversion layer¡ mostly having vertical length from 100 to 300 meters above surface level for all months of the year. The layer length was shorter when the relative humidity was greater. Temperature gradient changes to negative at the height of 1760-1580 meters above sea level. A lapse rate with the measure of 4Co/ Km during cold months and 6Co/Km during warm months was detected between the top of inversion layer and tropopause level. Maximum and minimum heights of tropopause were occurred during March and December 2009 (16494 and 19006 meters)¡ respectively. Result showed that according to global warming¡ variation in tropopause elevation trend in Shiraz station not only increase but also decrease. Tropopouse height changes from month to month and from year to year and we could not find any rule for it. Maybe these conflicts are because of short period of investigation. Tropopouse minimum temperature occurs in Jun and July and it is about -74 to -77.5 degrees Celsius .Maximum temperature occurs in December and January and it is closed to -68 degrees Celsius. Average annual value of tropopause temperature was estimated as (-71.6 Co). The coldest and warmest tropopause data were associated to the warm and cold months of the year¡ respectively. In seasonal scale¡ while the highest tropopause height occurred during winter (18138 meters)¡ the lowest elevation was associated to autumn (17158 meters). According to global regularity tropopause height increase in the warm months¡ but in this study it was proven otherwise because the maximum height of tropopause see in winter and it is due to the characteristics of a tropical latitude30 °and being in Subtropical Jet Stream path. Some discrepancies were found between our results and the findings of Australian investigator who analyzed Australian data (Khandu et al.¡ 2011). Discussion was made to justify these differences..Temperature gradient was found positive over the lower parts of stratosphere (up to 30 Km level). The highest or lowest increasing gradient was 1 or 2 oC per Kilometer¡ which happened during cold or warm months of the year¡ respectively.