Climatology
Yagob Dinpashoh; Saeid Jahanbakhsh-Asl; Asma Azadeh Garebagh
Abstract
In this study the values of potential reference crop evapotranspiration were calculated using the FAO-56 Penman Monteith method in six stations located in southern shores of Caspian Sea. Trends in annual ET0 values of the stations were analyzed using the Mann-Kendall test. Then to determine the relative ...
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In this study the values of potential reference crop evapotranspiration were calculated using the FAO-56 Penman Monteith method in six stations located in southern shores of Caspian Sea. Trends in annual ET0 values of the stations were analyzed using the Mann-Kendall test. Then to determine the relative importance of climatic variables on ET0 in a certain station factor analysis conducted. To do this, correlation matrix (R) of seven variables also called similarity matrix was constructed. The significance of correlation coefficients were tested. Results of trends in ET0 showed that in all the stations (except Noshahr) trends of annual ET0 were upward and significant. The slopes of trend lines were positive in all the stations. Factor analysis showed that the first two factors accounted the total variance in the range of 56.5 per cent in the Rasht to 79.6 per cent in the Sari. The largest loading of the first factor is attributed to sunshine hours in the station Rasht, however, it was maximum air temperature in all other sites. In the case of the second factor, the largest loading belonged to wind speed (in Rasht, Gorgan, Sari and Noshahr) and precipitation (in Ramsar and Astara). The findings of this study can be helpful in optimum management of regional water resources.
Climatology
amanollah fathnia; Saeid Rajaee; Farzane Borzo
Abstract
In this study, using Gorgan station data for the period 2010-1980 was studied precipitation trends. In order to extract precipitation trend the moving average and Mann-Kendall test was used. Also, using by SPI (standard precipitation index) drought period and by Markov chain probability event each of ...
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In this study, using Gorgan station data for the period 2010-1980 was studied precipitation trends. In order to extract precipitation trend the moving average and Mann-Kendall test was used. Also, using by SPI (standard precipitation index) drought period and by Markov chain probability event each of the different states drought or wet period was calculated. Then, using NOAA-AVHRR images fluctuations vegetation affected by the precipitation trend and by Markov chain probabilities alternation for each class were examined. Results showed has occurred in 2001-2007 and 1990-1994 Years wet period and in 1982-1986 and 2005-2010 drought period. Study of drought index showed precipitation trend in same period and has occurred wet period in 2001-2005 and drought period from 2005. According to Markov Probabilistic matrix probability alternation from severe drought to same is 0.6 and severe drought to moderate drought is 0.13. In same trend, have decrease semi-dense vegetation from with 494479 hectares in 1985 to less than 380,120 hectares in 2000. Density and area of Vegetation have increased from 2000-2005, but for the reason of drought decrease recently and with 0.48 probabilities will remain non vegetation class in same conditions. The most probability changing is related to sparse vegetation to non-vegetation with 0.41. On this basis, may be will changed 214060 hectares to non-vegetation.
Climatology
nahideh Jahedi; mohammadali Ghorbani
Volume 19, Issue 52 , June 2015, , Pages 63-63
Abstract
Being aware of decreasing or increasing trend of precipitation and discharge in watersheds has very important role in water resources management and the subjects relating to water engineering. In this study, the trend of precipitation and discharge at Qara-su River Basin in Ardebil has been studied in ...
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Being aware of decreasing or increasing trend of precipitation and discharge in watersheds has very important role in water resources management and the subjects relating to water engineering. In this study, the trend of precipitation and discharge at Qara-su River Basin in Ardebil has been studied in monthly, seasonal and annual timescales over the period from 1351 to 1382. For investigation of the existence or absence of a trend, Mann-Kendall test was used by detecting effects of all auto correlations coefficients, and Sen’s estimator was used at different significant level to evaluate the magnitude of the test. The results of the calculated values for precipitation and discharge data set indicated that the trend of the Qara-su River discharge was decreasing for both stations in annual timescale. Also, decreasing trend of discharge dataset was found for seasonal timescale in spring, autumn and winter in which significant trend belonged to winter season. Maximum value of decrease for discharge is for Doustbiglo station in spring (-0.62 m^3/s), and the minimum value of decrease for discharge in summer for this station, too. Furthermore, there was not significant trend for precipitation dataset in monthly, seasonal, and annual timescales.
Javad Behmanesh; Nasrin Azad Talatape
Volume 19, Issue 51 , April 2015, , Pages 41-58
Abstract
One of the atmospheric cycle properties is climatic changes which can cause the fluctuations in meteorological parameters. These fluctuations in many world regions are considerable and water and soil resources are affected by them. To prepare against undesirable effect of climate change and adopt suitable ...
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One of the atmospheric cycle properties is climatic changes which can cause the fluctuations in meteorological parameters. These fluctuations in many world regions are considerable and water and soil resources are affected by them. To prepare against undesirable effect of climate change and adopt suitable development programs and water resources management, it is necessary to investigate the meteorological variable changes. The objective of this research was to investigate the climate change in Urmia region. In this research, the changes trend of temperature, precipitation, relative humidity, sunshine and potential evapotranspiration were studied. To achieve this goal, Urmia synoptic station daily data with 40 years period (1971-2010) were used. The Mann-kendall statistical test at confidence level of 95% was used to investigate the significance of trend in the mentioned parameters. The results showed that the trend slope of maximum, minimum and average of temperature was positive and this trend in 95% confidence level was significant. Urmia precipitation was decreased with slope of -2.26 so that this decrease was significant. The sunshine had positive slope and significant trend, but the negative trend of relative humidity and the positive trend of potential evapotranspiration (0.0068) were not significant. The monthly investigations showed that the average temperature in all months had positive slope, but this slope was not significant in all months. The other parameters in some months had positive or negative slopes.
Yagoub Dinpazhooh; Faege Niazi; Hamed Mofid
Volume 19, Issue 51 , April 2015, , Pages 145-169
Abstract
The aim of this study is trend analysis of meteorological parameter including mean wind speed, min, max and mean air temperature, difference between the min and max temperature, pan evaporation, average relative humidity, sunshine hours, total precipitation, the number of days with precipitation more ...
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The aim of this study is trend analysis of meteorological parameter including mean wind speed, min, max and mean air temperature, difference between the min and max temperature, pan evaporation, average relative humidity, sunshine hours, total precipitation, the number of days with precipitation more than 1, 5 and 10 mm, the number of days with dust, number of the days with snow and the number of days with visibility less than 2Km, degree days based on 18 and 21 oC at Tabriz station during 1970-2005 in three time scales, monthly, seasonal and annually using the non-parametric Mann-Kendall (MK) method. Trend analysis was conducted using two methods, which are conventional MK (for series having insignificant autocorrelation coefficients) and modified MK (for other series) in three significant levels, 1%, 5% and 10%. Trend slopes were calculated using Sen’s estimator. Results showed that in annual time scale, pan evaporation, min, max and mean temperature and degree days based on 18 and 210C have significant increasing trends at 5% level but precipitation, number of the days with precipitation more than 1 and 5 mm and degree days based on 180C have decreasing trend (at 5% level). Other parameters did not show significant trend in annual time scale. Trend slope of annual precipitation was -2.28 mm/year and trend slopes of all three elements, average, max and min temperature were 0.06 0C/year. Observed trends in studying parameters indicate climate change in Tabriz.
Hossein Negaresh; Behrooz Sarisaraf; Mohammad Daraee
Volume 16, Issue 42 , March 2013, , Pages 239-259
Abstract
In this study at first, we supposed the normality of the data by some statistical parametric methods and then using non-parametric (Mann-Kendall) test, the non-linear trend of basin precipitation changes from a period of 45 years (1961-2005) relating to the synoptic station of Saqqez have been investigated. ...
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In this study at first, we supposed the normality of the data by some statistical parametric methods and then using non-parametric (Mann-Kendall) test, the non-linear trend of basin precipitation changes from a period of 45 years (1961-2005) relating to the synoptic station of Saqqez have been investigated. The statistical test results were: 1-The decreasing trend of spring precipitation is significant. 2-There is a significant increasing in summer precipitation. 3-The numerously at precipitation days at the thresholds 1 to 20mm has been decreased, but it increased at the large thresholds to 25mm. 4-The frequency trend of rainstorms days has the significant increasing.
