جستجوی مقالات مرتبط با کلیدواژه « annual precipitation » در نشریات گروه « کشاورزی »

One of the concerns of the human society is that the changes caused by global warming change the frequency and amount of precipitation and temperature. This study was conducted to investigate the trend of annual, seasons of cultivation, seasonal and monthly temperature and precipitation changes using the Mann-Whitney test at Ahvaz Meteorological Station. The study period consisted of two 31-year periods from 1957 to 2018. The results of this study showed that the minimum temperature had more changes compared to the average and maximum temperatures in the first 31 years (1957-1987) compared to the second 31 years (1988 to 2018). Mean comparison of minimum temperature and average temperature for the two periods showed that there was a significant difference at the 5% of probability level.  The means of the minimum and average temperature increased from 12.1 to 14.9 and 24.9 to 26.9°C, respectively. Mean comparison of the maximum temperature and precipitation for the two periods showed that there was no significant difference at the 5% of probability level. The averages of the maximum temperature and precipitation decreased from 37.5 to 36.8°C and 226.9 to 188.8 mm, respectively. Also, the study of precipitation trend in the two studied periods showed a high distribution of this climate parameter and a small change in the amount of this factor.

The Improvement and development of predictions in ungauged catchments require recognizing effective factors and understanding the interactions between different components of the catchments and hydrological response in different climatic zones. The most important factors affecting the flow duration curve (FDC) indices are precipitation and its characteristics. Since the flow duration curve represents the hydrologic response of watersheds, investigating and recognizing the effect of rainfall distribution on it can help to identify predictive factors for estimating the flow duration curve in ungauged catchments. The purpose of this study was to analyze the relationships between the number of rainy days and the indices FDC in the different climate zones of the country. Catchments of each climatic region were separated using the climate map of the country and overlapping it with the four-level border map of the watershed, and 314 hydrometric stations with the common period (1976–2011) in six climatic zones were selected. Flow duration curve using daily stream flow data were extracted by the Hydro Office software (2015) and indices of Q2, Q5, Q10, Q15, Q20, Q50, Q75, and Q90 were selected. The average of rainy days for each catchment was calculated and the regression relations between the FDC indices and the average of the number of rainy days in different climatic regions were extracted and analyzed. The results showed that the correlation between the indices of the first part of FDC with the number of rainy days in all selected watersheds of climatic zones had a weak and unreliable relationship for prediction and estimation of FDC in the ungauged catchments. But the relationships for the end parts of FDC (Q75 and Q90), were strong. It is noteworthy that the average coefficient of determination for the low flow indices (Q75 and Q90) with the average annual rainy days in catchments of different climatic zones was approximately equal to 0.66. This indicates the importance of the parameter of the number of rainy days as the predictor of the low flow indices associated with the end part of the FDC in different climatic zones. Therefore, it is suggested that the number of rainy days should be used as a predictive parameter for estimating the indices of the end section of FDC; its use for estimating other indices is not recommended.

Precipitation is one of the most important meteorological criteria whose quantity significantly varies throughout the earth. One of the methods to study precipitation trends in the past and present is the analysis of time series in different time scales. In this study, time series analysis was used for modeling and forecasting the average annual precipitation in Shiraz. Accordingly, the annual precipitation data in Shiraz were collected in the time interval 1951-2010. The results of this study indicated that 2.5, 5, 10, 12 and 20-year cycles cover in the study area and the third Compatible with a return period of 20-years and variance about 12 percent was dominanted in the study area. In the end, to make sure of the trend in the past and also forecasting the future precipitation, the ARIMA modeling was used. Finally, by trial and error in the ARIMA patterns family, a final pattern called M4(0,1,1) CON was selected as the optimum pattern in terms of statistical criteria. This pattern has suggested a 1.44 mm decline in precipitation until the year 2020. According to the results (the decreasing annual precipitation) and according to the climate change as a main topic, a comprehensive planning for the management of water resources unavoidable in Fars province and Shiraz city.

Interduction: Spatial and temporal improper distribution of precipitation is one of the major problems in the water district. Increasing population and reduction per capita fresh water has made freshwater resources as a renewable to a semi-renewable source (1).
Rainfall is one of the climatic variables that influence the ground water resources. The existence of models for predicting the annual precipitation and subsequent management of water resources in arid, semi-arid and also humid regions is useful . In this study, the simple regression models that relate the annual precipitation to the duration of 42.5 and 47.5 mm of precipitation from the beginning of autumn (t42.5 and t47.5, respectively) and mean annual precipitation (Pm), in Khuzestan (2), Kerman (3) and southern and western provinces of Iran (4) were evaluated using long-term daily precipitation data of Shahrekord and Yazd Weather stations and, if necessary, modified equations.
In this study, long-term daily precipitation data of Shahrekord and Yazd Weather stations (1360-1392) from Meteorological Administration of Chaharmahal and Bakhtiari and Yazd were prepared, completed and used for analysis. At each station the duration of 42.5 and 47.5 mm of precipitation from the beginning of autumn (t42.5 and t47.5, respectively) for each year, annual precipitation and mean annual precipitation for subsequent calculations were extracted. Then, the homogeneity and adequacy of data were checked using RUN Test. Equations of 1 to 8 were used for predicting the annual precipitation using 70% of the data. The relationship between observed and predicted annual precipitation were evaluated. Then the coefficients of equations were corrected by 70% of the data set using SPSS Software in Shahrekord and Yazd Weather Stations. The remaining 30% of data were used to validate the modified models. Index of agreement (d) and normalized root mean square error (NRMSE), were used to evaluate the models. The NRMSE values close to zero and d values close to 1 indicate proper operation of the model.
Results showed that the models with straight and reverse relationships between t42.5 or t47.5 and Pm were not suitable to estimate the annual precipitation in Shahrekord. However, these models were relatively acceptable for Yazd. While the simple regression model using t42.5, t47.5 and the long-term Pm as independent inputs could be able to predict the annual precipitation of Shahrekord and Yazd stations with acceptable accuracy.
Using the relationship between t42.5, t47.5 and Pa (equations of 1, 3, 4 and 7) for estimating the annual precipitation in Shahrekord and Yazd stations, NRMSE values obtained greater than 0.3 and d index less than 0.7 (Fig. 3 and 4). Furthermore , the models included t42.5, t47.5 and Pm versus Pa (equations of 2, 5, 6 and 8), had not acceptable results (Fig. 5 and 6). By modifying the above mentioned equations (models of 10 to 14 for Shahrekord and 15 to 19 for Yazd) and comparison of measured and predicted annual precipitation by the modified models, the results showed that the linear and inverse relationship between t42.5, t47.5 and annual precipitation could not be an appropriate model for Shahrekord Station (Fig. 7-A and 7-B and 7-C) and results of the evaluation of these relationships for estimating of the average annual precipitation of Yazd were relatively acceptable (Fig. 8-A and 8-B and 8-C results in Yazd station). While the simple linear model including the relationship between those time periods (t42.5, t47.5 ) and the long-term average annual precipitation with corrected coefficients could accurately estimate the annual rainfall in the Shahrekord and Yazd stations (Fig. 7-d and 7-H for Shahrekord and 8-D, 8-H for Yazd station). In order to validate the above results, the models were evaluated with the remaining 30% of the data . Results showed in Figs. 9 and 10. The NRMSE values in Figs. 10-A, 10-B and 10-C, confirm the validity of the relationship between t42.5, t47.5 and annual precipitation.

In this study, which lasted for 7 years due to two factors on annual precipitation and growing season precipitation ranges were Tang Laybid Yazd. The study area was the type of dominant vegetation types Artemisia aucheri. This type of plant was selected in three key. In every key area of 100 meters within 10 meters of each other transectbased and transect was placed on the slope 10 plots along each transect was calculated as 1 × 1 m square with a clear and proven choice and Available forage in each plot was measured by weighing and clipping method.. The results showed that the total amount of forage production with an annual rainfall level is 95 percent and The total yield of forage growing season with rainfall positive correlation. Rainfall during the growing season than other years was the appropriate rate will be higher yield

Forage quality is one of the most important affecting factors on the livestock performance which is affected itself by different parameters. In this research، four dominant and palatable range species were collected from Gorab Feraidonshar of Isfahan province in three phenological stages (vegetative، flowering and maturity) over two years (2007 and 2008). The plant species consist of Ferula ovina، Bromus tomentellus، Astragalus macruorus and Prangos uloptera. The samples were ground، and then nitrogen (N) and acid detergent fiber (ADF) were measured and the crude protein (CP)، dry mater digestibility (DMD) and metabolizable energy (ME) was estimated. Split plot design was used to analyze the data. Overall amount of crud protein، dry mater digestibly and metabolizable energy had significant differences in two years so that amount of these indices in 2007 (wet year with 725. 1 mm annual precipitation) was higher than those of 2008 (dry year with 284. 1 mm annual precipitation) in vegetative and flowering stages. However، amount of acid detergent fiber in 2007 was lower than that of 2008، but was not significance. In the maturity stage، significant differences were not found among the total indicators.