جستجوی مقالات مرتبط با کلیدواژه "تعرق پتانسیل" در نشریات گروه "جغرافیا"

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.

The accurate estimation of potential evapotranspiration is very important in water source management، agriculture، forestry and pasture sciences. Recently using of Geographical Information Systems (GIS) for accurate estimation has been developed and has showed good results. In this paper we estimate potential evapotranspiration in eastern Azerbaijan by Estefnz method. For calculation of coming net radiation (Rs) we used DEMSRTM images and solar analyst in ArcGIS software for 31 May، 10-11 am. After calculation of slope and aspects through digital elevation model، net radiation was estimated. The average temperature calibrates for elevation was imported in equation. Final maps show that the amount of potential evapotranspiration is between 0~15 mm/hour. Northern aspect and areas with high temperature have the higher potential evapotranspiration. Elevation and aspects are important factors than other factors in potential evapotranspiration control in the study area. The amount of evapotranspirtaion is higher than precipitation and therefore it is better that agricultural activities move to higher areas

Potential evapotranspiration () is one of the most important component of hydrological cycle for irrigation systems scheduling, preparing input data for water balance hydrological models, and assessment of hydrological effect of climate change. One of the major issues of human societies in the present century is global warming due to green house gases increasing and water resources crisis. As a result, climate change may have significant effects on some of the hydrological parameters such as runoff, evapotranspiration, soil moisture and groundwater. Also, evapotranspiration is most important component of hydrological cycle after precipitation and usually crop water requirement determined using. Any change in climatological parameters due to global warming will affect evapotranspiration too. Eventual global warming may increase dry conditions in the world with increase of evapotranspiration and intensification of desertification. Therefore, Earth’s global warming may change the hydrological cycle components and global water resources will re-distribute in the time and place. This may intensify desertification in arid and semi arid countries such as Iran. 2- In this study values computed using the Blaney- Cridle method for the 6 synoptic stations located at southern part of Aras river basin in the period 1986-2008 (23 years). Furthermore, trend of and some meteorological variables (precipitation, maximum temperature and minimum temperature) which affect it were analyzed in both annual and seasonal time scales. Data used for computing involves: mean daily temperature, minimum relative humidity, wind speed (m/s) and sunshine hours. For trend computing, the effects of autocorrelation cofficients until 31 lags were included. Then trend analysis was performed with conventional MK method (for series with insignificant autocorrelation) and modified MK (for series with significant auto correlation). Mann – Kendall method is one of the most commonly used non parametric tests for considering trend in different hydrological and climatological variables. Test statistic Z was obtained from Mann-Kendall equations compared with normal Z in significance level. If Mann-Kendall test statistic absolute value, Z, was more than 1.645 then the trend (increasing or decreasing) considered being significant in 10% level. If it was more than 1.96, trend considered being significant in 5% level and if it was more than 2.33 then trend level will be 1%. In addition to trend test, slope of trend line also estimated using the Sen’s slope estimator. 3- Results indicated that variation trend of as one of the main components of hydrological cycle at southern part of Aras river basin has spatial and temporal variations. Among all stations, Khoy experienced the most sever significant increasing trend (P<0.05) at annual time scale. At this station strong decreasing trends detected for minimum relative humidity, which was stronger than other stations. At this station some parameters related to air temperature and wind speed showed increasing trends. trend line slope estimated about 25 mm/year at the mentioned station. Increasing insignificant trends detected for at Makoo and Ahar stations at annual time scale. At this station decreasing trend for relative humidity experienced. Other station’s trend was detected to be decreasing (but insignificant). At seasonal time scale, combinations of both positive and negative trends observed for stations. Khoy station’s seasonal trend for all seasons was positive (autumn was significant at 5% level) and at Parsabad station was negative (but insignificant). Among considered parameters, trends of sunshine hours at all stations were significant at both seasonal and annual time scales. Minimum, maximum and mean air temperature in annual time scale at all stations had increasing trends. Trends of autumn precipitation at all stations were decreasing. Decreasing trends observed for wind speed at all stations (except Jolfa and Parsabad) at annual time scale. 4- Results showed that among all stations, Khoy had highest significant increasing trend which is due to significant increase in wind speed, sunshine and significant decrease in relative humidity values. Maximum value of trend line slope at this station observed at annual time scale which was estimated equal with 25 mm/year. Among all stations the strongest decreasing trend slope belonged to Parsabad station (at annual time scale) equal with 8.4 mm/year. Among parameters which their effects considered on evapotranspiration more variation related to autumn sunshine hours in Ardebil station which is about 3.7 hours/year. The most decreasing precipitation trends observed at Ahar and Parsabad station which the slope of trend line was about 2.4 mm/year.