Irrigation
M. Gaznavi; A. Mosaedi; M. Ghabaei Sough
Abstract
Introduction: Drought is a climatic phenomenon and an integral part of climate fluctuations that occurs periodically and intermittently throughout the world and across all climates. However, the magnitude of this natural hazard in arid and semi-arid regions, such as most parts of Iran, is more acute ...
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Introduction: Drought is a climatic phenomenon and an integral part of climate fluctuations that occurs periodically and intermittently throughout the world and across all climates. However, the magnitude of this natural hazard in arid and semi-arid regions, such as most parts of Iran, is more acute due to the high sensitivity and weakness of these areas, and its effects may persist for years after the occurrence of drought. Drought is a multifaceted phenomenon as precipitation, temperature, evaporation, wind and relative humidity play important roles in the drought characteristics such as occurrence, severity, and magnitude. Climate change and global warming, and in some cases displacement of meteorological stations cause heterogeneity in time series of meteorological data. Therefore, the purpose of this study was to investigate the homogeneity and break point in precipitation time series data and the effects of a break point in drought characteristics in some synoptic stations in Iran. Materials and Methods: In this study, homogeneity of rainfall time series data at two time scales of annual (water year) and plant growth periods in some selected synoptic stations of Iran with different climatic conditions was investigated. For this purpose, four tests including Standardized Normal Homogeneity test (SNH), Buishand’s Range test (BHR), Buishand’s U test (BUR) and Petite’s test were applied and the break points were determined. Then, at the stations with break points in the precipitation data series, the drought severity values were determined using four indices of SPI, SPEI, RDI and eRDI, for two periods, (before and after of the break points). Then drought characteristics based on Markov Chain Model and Transition probability matrix including vulnerability, reliability, reversibility and stationary of three condition of droughts (dry, normal and/or wet condition) were determined for the two time scales periods (annual and plant growth periods). Then, the differences between the characteristics for the two periods were investigated. Also, the characteristics of drought-free time intervals for the two periods based on Run’s theory were determined and compared. Results and Discussion: Based on the homogeneity tests, precipitation data of Arak and Tabriz stations for two scales of annual and plant growth periods have break points. According to the results, in the most cases, the second period's reversibility was lower than the first period. Reliability and vulnerability also decreased and increased in all cases in the second period, respectively, compared with the first period. In most cases, there was an increase in stationary of drought in the second period relative to the first period. The rate of change in the probability of survival of the normal and wet condition in both periods was increasing and in some cases decreasing. Regarding the results of Run’s theory at the growth periods scale, the average and maximum duration of drought periods increased in all cases in the second period. The minimum, average and maximum severity of drought periods also increased in most cases in the second period. The minimum, average, and maximum values increased in most cases in the second period. On an annual basis, the number of drought periods in most cases has increased in the second period. The average and maximum duration of drought periods increased in all cases in the second period. The minimum, average, and maximum severity of drought periods also increased almost in all cases in the second period. Minimum, average, and maximum of drought magnitude values increased in most cases in the second period with respect to the first one. The minimum, average and maximum values of the drought-free durations (interval time without drought conditions) in most cases were lower in the second period. At the annual scale, the minimum duration of drought was one year in all cases and no change was found between the time slices. The average duration in most cases was lower in the second period. Conclusion: The results show that the rainfall data of Arak and Tabriz stations have break points in the time scales of plant growth period and annual periods. The reliability was decreasing while the vulnerability of drought was increasing in the second period, indicating an increase in drought occurrence in recent decades. Moreover, the probability of drought stability (stationary) in the second period increased in most cases. The average and maximum duration of drought periods also increased in the second period. The minimum, average, and maximum drought severity, and the minimum, average, and maximum of magnitude of drought periods were higher during the second period. In most cases, the minimum, average, and maximum of severity and magnitude of drought-free time intervals were lower in the second period. In general, difference in the characteristics of drought before and after of precipitation break point can be due to increased evapotranspiration, as a result of global warming, intensifying the effects of drought. Moreover, based on the results of the eRDI index, the climatic conditions became drier in both stations and time periods. In other words, it can be stated that the effective rainfall has decreased to some extent in recent years compared to the early years of the study period. Further studies are needed to assess the changes in drought characteristics in all synoptic stations in the country having long-term data.
P. Moradzadeh; H. Ojaghlou; Mohammad Ghabaei Sough
Abstract
Introduction: The average of irrigation efficiency is less than the global average due to improper irrigation systems and traditional water management practices in the field. The use of modern irrigation systems is one of the most important ways to cope with the water shortage crisis in Iran. ...
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Introduction: The average of irrigation efficiency is less than the global average due to improper irrigation systems and traditional water management practices in the field. The use of modern irrigation systems is one of the most important ways to cope with the water shortage crisis in Iran. However, it is necessary to evaluate the effective factors on performance of irrigation system. In present study, a zoning map of suitable land for implementation of sprinkle irrigation system was prepared using AHP method with considering the criteria such as chemical characteristics of water, soil properties, topography, climate, social and economic factors in the Zanjan plain.
Materials and Methods: The present study was carried out using collected data from Zanjan plain that located in northwest of Iran and east of Ghezel Ozan River. The total study area is about 4705 km2 and the average rainfall and temperature in region are 259 mm and 10.9 °C, respectively. The first step in the AHP method is to create a hierarchical structure. For this purpose, each of the criteria was rated 1 to 9 based on paired comparisons done by experts and then classification maps were prepared for each of them. In order to provide zoning maps for water and soil factors, data of more than 2000 wells and 111 soil samples were collected, respectively. In addition, data of 13 Meteorological stations were used to prepare zoning maps of climatic factors such as wind speed and temperature. In this research, a topographic map with a scale of 1/25000 was used to investigate the ground slope effect. More than 60 interview forms were completed to produce maps related to socio-economic factors. Zoning maps were prepared using the Kriging interpolation method in ArcGIS software. Finally, the weight of each criteria was calculated according to the scores that obtained in the previous stage and then land classification map was produced by applying the obtained weights on each criteria. In order to evaluate the situation of sprinkle irrigation projects, location of 52 farms equipped with sprinkle irrigation system obtained from the agricultural organization of Zanjan province.
Results and Discussion: Regarding the quality of water resources, 40.3% and 21.0% of area were classified in most suitable and suitable classes, respectively and about 10.4% was evaluated in the inappropriate class in order to implementation of sprinkler irrigation. In terms of the soil physical and chemical properties, about 38.4% of plain were classified as "most suitable", 22.8% as "suitable" and 24.7% as "inappropriate" class. In relation to topographic criteria, it can be stated that about 85% of area are in good condition, so that the ground slope in most of the lands is less than 10%. Based on climate criteria and specifically wind speed factor, about 61% of the plain was classified as "good" and "very good", while about 39% was in medium and low class. In terms of social and economic criteria, most of area were found to have a good rating, so there is no particular limitation in this regard. The results of the paired comparisons between criteria showed that, social and climatic criteria have the lowest and highest weight, respectively. The value of the inconsistency rate was calculated about 0.07, which indicated the acceptability of the gained weights. An examination of land feasibility map showed, about 33.4% of the region is suitable for implementing sprinkle irrigation system. About 29.5% and 25.8% were evaluated without limitation and low limitation, respectively. Also, about 10.3% was not recommended for use of sprinkle irrigation. The assessment of the location of implemented projects showed that 44.2% of the projects were in suitable or perfectly suitable classes of land. The rest of the projects (55.8%) were implemented in medium or unsuitable classes.
Conclusion: The results obtained from the AHP method showed that wind speed factor has the most weight and importance in selecting sprinkle irrigation system. Generally, in most farms of the region, there is no significant limitation on the implementation of sprinkler irrigation system. Due to low water quality and high wind speed in a small part of the study area that located in northern and eastern, the use of these systems is not recommended. The results showed that some of the sprinkle irrigation projects have been implemented in lands with low-class and it is essential to improve or change these systems.
Mohammad Ghabaei S; Hamid Zare Abyaneh; Abolfazl Mosaedi; S. Zahra Samadi
Abstract
Introduction: Drought is a recurrent feature of climate that caused by deficiency of precipitation over time. Due to the rise in water demand and alarming climate change, recent year’s observer much focus on drought and drought conditions. A multiple types of deficits and relevant temporal scales can ...
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Introduction: Drought is a recurrent feature of climate that caused by deficiency of precipitation over time. Due to the rise in water demand and alarming climate change, recent year’s observer much focus on drought and drought conditions. A multiple types of deficits and relevant temporal scales can be achieved through the construction of a joint indicator that draws on information from multiple sources and will therefore enable better assessment of drought characteristics including return period, persistent and severity. The Standardized Precipitation Evapotranspiration Index (SPEI) combines information from precipitation and temperature in the form of water surplus or deficit according to Standardized Precipitation Index (SPI). Rainfall over some regions of Iran during some resent year was below average while mean and maximum temperatures were very high during this period, as was evaporation. This would suggest that drought conditions were worse than in previous recent periods with similarly low rainfall. The main objective of this study is to assess the influences of humidity on the SPEI index and investigate its relation with SPI and Reconnaissance Drought Index (RDI) over six different climatic regions in Iran.
Materials and Methods: Iran has different climatic conditions which vary from desert in central part to costal wet near the Caspian Sea. In this study the selection of stations was done based on Alijani et al (2008) climatic classification. We chose 11 synoptic stations from six different climatic classes including costal wet (Rasht and Babolsar), semi mountains (Mashhad and Tabriz), mountains (Shiraz and Khoram Abad), semi-arid (Tehran and Semnan), arid (Kerman and Yazd) and costal desert (Bandar Abas). The Meteorological datasets for the aforementioned stations were obtained from the Iran Meteorological Organization (IRIMO) for the period 1960-2010. The compiled data included average monthly values of precipitation, minimum and maximum air temperature, mean relative humidity, sunshine hours) and wind speed at 2 m height. A probability-based overall water deficit assessment was achieved from multiple drought-related indices (i.e. SPEI, SPI and RDI). The humidity conditions were monitored for given stations based on each index during annual, short term (1, 3 and 6 months) and long term (9 , 12, 18 and 24 months) periods. This research further examine the Locally Weighted Scatter plot Smoothing (LOWESS) graphical method and nonparametric Man- Kendal test to evaluate the trends associated with humidity deficiency in annual and monthly time scales during 51 years period (i.e. 1960-2010).
Results and Discussion: Our results revealed that the maximum correlation between SPEI index with indices of SPI and RDI was achieved in the coastal wet region and with a declining trend in relative humidity condition in the rest of the regions, this correlation is down over both short- and long-term periods. A comparison between SPI and SPEI also performed that the SPI index was able to reflect prolonged drought over the costal wet region where it showed significant inconstancy in desert and semi desert regions. SPEI result suggested substantial deficiencies in relative humidity at the beginning of 1997 during long term period which indicated an increasing trend of drought statues during last decades. Overall, according to the results of SPEI index in 1month periods monthly drought assessment showed a declining trend in drought magnitude during autumn, winter and spring season months (October to June) at investigated stations excepts Tehran and Shiraz stations and with a potential deficiency in relative humidity conditions. Unlikely, annual trend showed increasing trends in drought frequency and persistent over last decade.
Conclusion: Our results can be summarized as below:
Focusing on various types of deficits, the result of humidity based deficiencies indicated that for semi-mountains, mountains, semi-arid, arid and costal desert regions the period of 1997 to 2010 has a large total moisture shortage over all climatic regions. Most of the climate stations showed moisture deficits (decline trends) during October to June (9-month) at many stations expect Tehran and Shiraz stations which revealed a significant increasing over 51 years. We recommend using SPEI index for arid and semi-arid regions because it includes temperature variability in drought model so it reflects drought conditions better than other indices. Furthermore, three drought indices (i.e. SPEI, SPI and RDI) have similar sensitivity to water deficits over wet climatic regions; therefore, each of those indices can be used.
A. Mosaedi; S. Mohammadi Moghaddam; M. Ghabaei Sough
Abstract
Introduction: Weather features and their variations have an important role in the yield of agricultural products, especially in rain-fed conditions. The main metrological variables that affected yields consist of precipitation, temperature, soil moisture and solar radiation. Also, drought is one of the ...
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Introduction: Weather features and their variations have an important role in the yield of agricultural products, especially in rain-fed conditions. The main metrological variables that affected yields consist of precipitation, temperature, soil moisture and solar radiation. Also, drought is one of the major constraints to production, especially the mid-season drought which occurs during the podand seed formation stages and the terminal drought which occurs during the pod filling stage. The results of investigating the relation between drought indices such as Standardized Precipitation Index (SPI), Palmer Drought Severity Index (PDSI), Crop Moisture index (CMI) and Z index with crop yields indicated the capability of these indices to estimate variations in crop yields. The objective of this study in the first step is investigation of relations among wheat and barley crop yields with climatic variables and SPI and RDI drought indices based on Principle Component Analysis (PCA) method at Bojnourd, Mashhad and Birjand stations. In addition, by selecting the prominent variables via PCA method, the best models of estimating each crop’s yield based on multivariate regression methods at selected stations were determined.
Materials and Methods: In this study, the relationship between yields of rain-fed wheat and barley with weather variables consisting of minimum, mean and maximum temperature, precipitation, evapotranspiration and drought indices including SPI and RDI were investigated and modeled at Bojnourd, Mashhad and Birjand stations. For this purpose, the values of each variable were calculated for 34 time scales of 1, 2, 3, 4, 6, and 9 months and wet periods (nine 1-month periods, eight 2- month periods, seven 3- month periods, six 4- month periods, two 6- month periods, one wet period (5 or 7-month) and one 9-month period). After that, the main influencing variables were chosen among investigated time periods for each variable by using the method of principal component analysis (PCA). In continuation, the selected variables via PCA technique were used in the multivariate regression methods to create the best model of predicting wheat and barley yields based on each mentioned variable and combination of them. The performance of the established model was evaluated based on Ideal Point Error (IPE) criteria and the best predicting model of wheat and barley was selected for each region.
Results and Discussion: The results showed that applying PCA technique as a powerful statistical tool leads to decrease of the error and inflation of constructed models. This is done by reducing the volume of data and selecting influencing variables. Based on the PCA results by choosing only four components the 90 percent and greater than variation of crop yields are estimated and the first component includes time periods of spring and winter months. Investigation of the results of the best model at the given stations based on IPE criteria show that the constructed models based on variables of SPI index have more accuracy for predicting yields of wheat and barley at station of Bojnourd, at Mashhad station the created models based on a combination of variables and at Birjand station a model based on a combination of variables and a created model according to RDI variables was used that has more accuracy for predicting yields of wheat and barley, respectively. Comparing the estimated and actual values of wheat and barley yields indicate that the correlation coefficients of the models when applied to estimate the yield of wheat and barley at Bojnourd station resulted in 68 and 69 percent, at Mashhad station 89 and 86 percent and at Birjand station 66 and 74 percent, respectively.The performance evaluation graph shown in Fig. 1 can be used to illustrate model performance and to diagnose model bias.
Conclusion: According to the results, a relation between crop yields and combination of metrological variables and drought indices is more positive and stronger than only metrological variables combination. The results showed that the variables of temperature, precipitation and evapotranspiration are to be considered. Also, the evaluation model indicated that the RDI index is more suitable for predicting rain-fed wheat and barley yields.
H. Zareabyaneh; M. GHobaeisoogh; Abolfazl Mosaedi
Abstract
Introduction: Drought is a natural and recurrent feature of climate. The characterizations of it may change under the effect of climate change in future periods. During the last few decades a number of different indices have been developed to quantify drought probabilities. Droughts are caused by disruptions ...
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Introduction: Drought is a natural and recurrent feature of climate. The characterizations of it may change under the effect of climate change in future periods. During the last few decades a number of different indices have been developed to quantify drought probabilities. Droughts are caused by disruptions to an expected precipitation pattern and can be intensified by unusually high temperature values. Precipitation-based drought indices, including the Standardized precipitation index (SPI), cannot identify the role of temperature increase in drought condition and in addressing the consequences of climate change. Recently, two new standardized drought indices have been proposed for drought variability analysis on multiple time scales, the Reconnaissance Drought Index (RDI, Tsakiris et al., 2007) and the Standardized Precipitation Evapotranspiration Index (SPEI, Vicente-Serrano et al., 2010). The objective of this study is to evaluate the characterization of wet and dry periods under the effect of climate change according to SPEI index in synoptic station of Hamedan for the next thirty years (2011-2040).
Materials and Methods: In this study, the indices of SPEI, SPI and RDI were investigated and the SPEI index as a multiscalar and suitable index was used to detect, monitor, and explore the consequences of global warming on drought conditions in synoptic station of Hamedan (airport). For this purpose, the period of 1981-2010 was chosen as the base period and the simulation of the future climate variables were done based on A1B, A2 and B2 emissions scenarios and performance of multi model ensemble via LARS-WG5 model for the period of 2011-2040. The performance of the multi model ensemble was done by using five global climate models including IPCM4, MPEH5, HADCM3, GFCM21, and NCCCS in the IPCC Fourth Assessment Report (Semenov and Stratonovitch, 2010). By simulating the values of precipitation ,and the values of temperature and the values of estimated evapotranspiration , the values of SPEI, RDI and SPI indices were calculated annually and 1, 3 and 6 months (short- term period) and 12, 18 and 24 months (long- term period) time scales for the base period and the three next decades. Then, the relation among them was computed and investigated via correlation coefficient. Then, by monitoring the humidity condition via SPEI index, the characterization of wet and dry periods including period numbers, longest period, total deficit or surplus, and maximum deficit or surplus were derived based on Run theory and were comprised for the base period and three future decades.
Results and Discussion: Evaluation of LARS-WG5 model for base period showed that the model was able to simulate minimum and maximum temperatures and precipitation data with high accuracy based on statistic error and can be used to generate data for future years according to emission scenario. According to the simulated results of performance of multi model ensemble, the average values of mean temperature and precipitation will increase by 0.820C and 2.5 % for A2 scenario, respectively. In addition, the minimum and maximum temperatures have increased in all of the months according to the three scenarios in comparison with the base period. The correlation results between the investigated indices showed that the maximum and minimum of correlation can be observed between SPI & RDI and SPEI & SPI indices in the base period and future decade for each scenario, respectively. Drought assessment based on the SPEI index in the base period shows that the main drought episodes occurred in the 1999 to 2001 that were consistent with FAO report (2006). Comparison of wet and dry periods in relation to the base period showed that the number of dry periods will increase in time scales of 1 and 3 months and will decrease in other long-term time scales.
Conclusion: Climate change and its effects are among the main challenges of water resources management in the present century. In this study, the effects of this phenomenon on drought monitoring and change of characterizations were investigated. For this purposes, we used daily meteorological variables during thirty years (1981-2010) from Hamedan Synoptic station. The results of drought monitoring were based on SPEI index, and it revealed the high variability of humidity condition in the first decade of simulation in comparison with the second and third decades. This issue indicated that this decade requires more attention and management measurements. Also, according to the results of the derived characterization via Run theory, the number of dry periods will decrease and persistence of the longest dry period and consequently the volume of deficit will increase in the next three decades. In addition, the total volume surplus of wet periods will decrease in relation to the base period that can be interpreted as the increasing of moisture deficit in future decades The SPEI is based on precipitation and temperature data, and it has the advantage of combining multiscalar character with the capacity to include the effects of temperature variability on drought assessment. Thus, we recommend SPEI, as a suitable index for studying and identifying the effect of climate change on drought conditions.
A. Mosaedi; M. Ghabaei Sough
Abstract
Abstract
SPI is based on fitting a gamma distribution to precipitation amounts in selected periods. Based on current research, the gamma distribution may not be fitted to annual precipitation of some regions. In order to evaluate this subject, annual precipitation have been used during 1958- 2007 at ...
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Abstract
SPI is based on fitting a gamma distribution to precipitation amounts in selected periods. Based on current research, the gamma distribution may not be fitted to annual precipitation of some regions. In order to evaluate this subject, annual precipitation have been used during 1958- 2007 at 11 Synoptic Stations in Iran. In first step, values of SPI and frequency of different classes of drought severity were calculated. The Kolmogorov– Smirnov test is used to assess the goodness of fitting most appropriate distribution function to annual precipitation. Then, according to equi-probability transformation the values of SPI were modified. The impact of applying most appropriate distribution function was evaluated to change the frequency of different classes of drought severity in Modified Standardized Precipitation Index (MSPI). The results showed that annual precipitation in all stations do not fallow Gamma distribution as appropriate distribution function except for Rasht station. Using appropriate distribution function in a MSPI leads to changing the frequency and/or displacement of different classes in SPI. So displacements occurred in all classes of drought severity at Tehran and Gorgan synoptic stations. The Gorgan station with 15 events has the most changes in frequency classes.
Keywords: Standardized Precipitation Index (SPI), Gamma distribution, Equi-probability transformation, Displacement of different classes, Iran
M. Ghabaei Sough; A. Mosaedi; M. Hesam; A. Hezarjaribi
Abstract
Abstract
Process of evapotranspiration (ETo) is a major component of the hydrologic cycle that its accurate estimation plays an important role to achieve sustainable development in water balance, irrigation system design and planning and management of water resources. Being a function of different metrological ...
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Abstract
Process of evapotranspiration (ETo) is a major component of the hydrologic cycle that its accurate estimation plays an important role to achieve sustainable development in water balance, irrigation system design and planning and management of water resources. Being a function of different metrological parameters and their interactions, evapotranspiration is a complex, nonlinear phenomenon. Preprocessing input parameters to select appropriate combinations is complex when modeling nonlinear systems. Using these methods reduce steps by trial and error by recognizing most important parameters for modeling by intelligent methods. In this study, two methods of stepwise regression (FS) and gamma test (GT) were used for preprocessing input parameters in multi layer perceptron neural network (MLP) to estimate daily estimation of ETo at Shiraz synoptic station. To evaluate the effect of Input parameters preprocessing in artificial neural networks using different statistical error criteria, ANN-FS and ANN-GT both with pre-processed parameters were compared against each other and also with ANN model without pre-processed parameters. The results showed that all three models have a high degree of accuracy to estimate daily ETo. ANN-GT model represented a determination coefficient (R2) of 0.9995 and the root mean square error (RMSE) of 0.0483. For ANN-FS and ANN models R2 values were 0.9984 and 0.9994 respectively and RMSEs were 0.0874 and 0.0548 respectively. Although the accuracy of ANN-GT model was slightly greater than ANN, but the ability of determination of importance of input parameters, education and recognition of the best combination of input parameters with 800 data in this study, makes this model a useful tool for fast preprocessing input parameters to model evapotranspiration.
Keywords: Potential evapotranspiration, Artificial neural networks, Gamma test, Stepwise regression, Shiraz synoptic station
