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Showing 16 results for Spi
Mohamad Ekrami,
Volume 7, Issue 20 (5-2013)
Abstract
Morteza Khodagholi, Mahnaz Kavousi, Abbas Ali Arvin, Razieh Sabouhi,
Volume 7, Issue 21 (7-2013)
Abstract
The long-term monitoring and forecasting of climatological parameters in each zone can be the suitable technique to deal with the effect of climatic fluctuations (drought, flood and etc.) Therefore, it is mportant to identify the effective drought factors in this region such as Zayanderoud watershed basin that it is located in semi arid region. The purpose of this study is to identify the Zayanderoud watershed drought and the effect of Southern Oscillation Index (SOI) and the North Atlantic Oscillation (NAO) on climate conditions and climatical parameters such as precipitation. In this regard, the long-term time series (1970-2009) of synoptic and climatology stations and the data of NAO and SOI was prepared from the site of NOAA. So, to determine the extent and impact of the NAO and SOI on drought, the correlation was calculated between standard precipitation index at the end of May for 3, 5 and 8 months time scales and SOI and NAO indexes. Also, the correlation coefficients are investigated between seasonally and monthly precipitation in this watershed and the mentioned indexes The results show that the precipitation of Meime, Najaf abad, Freydan, Freydoonshahr, Daran, Chadegan, Koohrang has statistically significant negative correlation with SOI. However, Esfahan, Freydan and Freydoonshahr have statistically significant negative correlation with NAO and Shahreza, Abade and Varzane that are located in the dry zone show no statistically significant correlation with any signals and SOI and NAO indexes. The mentioned indexes synchronize and unsynchronize are showed the statistically significant correlation with seasonally and monthly precipitation in different parts of the watershed.
S.adib Banimahd, Davar Khalili,
Volume 8, Issue 24 (6-2014)
Abstract
In the present research, probabilistic drought characteristics, i.e., steady state probabilities of drought occurrence, drought termination and expected residence times for each severity class were studied for Mazandaran province, utilizing a modified version of Standardized Precipitation Index (SPI) for 3-, 6- and 12-month time scales and Markov chains. According to results, drought termination time and expected residence time of drought classes with increasing time series steps (from 3- to 12-month) showed increasing and decreasing trends, respectively. Furthermore, log-linear models were applied for short term prediction of drought class transition corresponding to SPI 12-month. Results also indicated that the lowest frequencies occurred during direct transitions from a given drought class to two/three classes with higher (lower) severity. Furthermore, the occurrence probability of each drought class from two previously given drought classes was calculated and validated by the log-linear model. Results of validation of the predictions during 2001 confirmed appropriateness of predictions corresponding to drought class severity for a 2-month lead time from two previous months, particularly when drought was initiating or dissipating. It is concluded that log-linear predictions of drought severity class can be used as a useful tool for early warning to farmers and water managers early in autumn.
Somaye Hejabi, Javad Bazrafshan,
Volume 9, Issue 28 (7-2015)
Abstract
One of the most important and widely used indices for drought monitoring, especially in our country, is the Standardized Precipitation Index (SPI). This index is the basis for drought definition and monitoring in most of studies. In this study, two procedures were used for the calculation of SPI. In the first procedures, with the hypothesis that the precipitation data follow the gamma distribution and in the second, using the optimum distribution, the SPI series in three timescales of 3, 6 and 12 months were calculated. In the next step, the t-student test was applied to consider significance differences in the results of two procedures. In three time scales, on average, the frequency of significant difference in the results of two procedures, was maximum in normal class and thereafter, across the wet classes, extreme wet class and mild wet class and across the drought classes, mild drought class and moderate drought class, had the most frequency of significant differences. The results of the study showed that the calculation of the SPI based on gamma distribution give rise to the wrong diagnosis of the SPI classes. Then, calculation of SPI on the basis of the optimum distributions instead of blindly using of gamma distribution is proposed, in order to more accurate drought monitoring for the suitable management of drought.
Saeed Farzin, Hojat Karami, Shahab Nayyer, Elham Zamiri,
Volume 11, Issue 39 (1-2018)
Abstract
Cylindrical weir is one of the hydraulic structures that due to measurement flow rate and flood control are used, and is less expensive than similar structures. In this study, the numerical model validation is performed with an accredited experimental model in three different diameters (11, 9 and 6.35 cm), and in three different angles (45, 90 and 135 degree) toward the wall with Flow3d software. According to the simulation, in the results with k-ε turbulence model there is a good adaptations than the other turbulence models such as the RNG and LES model, and the correlation coefficient (R2=0.965), indicated that the k-ε turbulence model is the best. Due to increasing the length of weir in oblique position and changing the situation of spillway from direct position to oblique position, discharge coefficient will increase, so leads to increasing of discharge. The results show that in models with complementary angles, because of the similarity of these models in the flow pattern, the discharge coefficients will be almost equal to each other. With increasing the diameters of spillway from 6.35 cm to 11 cm discharge coefficient reduced up to 50%. Maximum of the correlation coefficient between discharge and discharge coefficient for cylinder with 11 cm diameter is equal to 0.95 that show high Effectiveness of discharge on discharge coefficient.
Dr Massoud Goudarzi, Dr Boroumand Salahi, Dr Seyed Asaad Hosseini,
Volume 12, Issue 41 (7-2018)
Abstract
Evapotranspiration is a major component of the hydrological cycle which shows the amount of water loss. Since the amount of evapotranspiration is directly associated with climate variables and is related with the amount of changes in climate parameters, particularly temperature plays a key role in this regard. Therefore, in this study, possible impacts of climate change on evapotranspiration rate are estimated in the Lake Urmia Basin as a wet basin in the country. The basin nowadays is faced with drought and reduction of water level. Predictions of the changes in the lake, were examined Under scenarios A1B, A2, B1 and B2 using LARS-WG and SDSM Statistical Downscaling models and HadCM3 general circulation model output in the next three periods (2030-2011, 2065-2046 and 2099-2080) . Using the predicted climate parameters changes, Evapotranspiration rates in the basin in monthly and seasonal periods, was calculated using Hargreaves Samani and Priestley Taylor. The results showed an increase in long-term average minimum temperature in the basin between 0.2 to 3.4 degrees and a maximum temperature increase of between 0.9 to 2.9 degrees in future periods compared to the base period (1990-1961). The estimate of evaporation rate shows an increase in monthly and seasonal time series in future affected by the temperature. The increase would be between 2.4 to 15 percent on long-term average in the basin. The results can be used in the management of groundwater and surface water resources, irrigation and drainage projects, estimating crop water requirements, irrigation scheduling and environmental studies and watershed plans.
Maryam Mirakbari, Farizhendi Ghasem Mortezaii, Saravi Mohsen Mohseni,
Volume 12, Issue 42 (10-2018)
Abstract
Groundwater and surface water resources are severely affected by the lack of rainfall. Several indices provided for evaluation of drought based on meteorological and hydrological variables. In this study condition of meteorological and hydrological drought evaluated by SPI, SPEI, SDI and GRI. The correlation of indices was evaluated at different time scales. Base on the results SPEI has higher correlation than SPI with SDI at 9 and 12 months time scales and in the same month and one month later. Also SPEI has highest correlation with GRI at 24 and 48 months time scale that shows the impact of meteorological drought on groundwater level after two years and more. Knowledge of interval time between of meteorological drought as the main factor of drought would help to manager and planner for management practices in order to cope with drought due to lack of surface and ground water resources.
Professor Alimohammad Khorshiddoust, Professor Behrooz Sarraf, Professor Bagher Ghermez Cheshmeh, Professor Fatemeh Jafarzadeh,
Volume 12, Issue 42 (10-2018)
Abstract
Heavy rainfall is one of the most important climatic events, and if the correct planning is not done, it will have destructive environmental and economic impacts and will be removed without exploitation. This study is trying to forecast changes of the future heavy rainfall in southern coasts of the Caspian Sea with regard to global climate change in the period of 2011-2030. For this purpose, changes in the pattern of 10, 20 and 25 mm and more rainfall were analyzed based on rainfall data of six synoptic stations (Anzali, Astara, Babolsar, Gorgan, Noshahr, Ramsar and Rasht). Daily rainfall data was simulated in the period 1961-2009, after verification of their accuracy and Correctness, using the Lars-wg model. After comparing the simulated values with the current period data, the daily rainfall values were predicted for the upcoming period (2011-2030). The eleven indexes of the R-Climdex global model were calculated for the current period and the upcoming period. Among these, three heavy rainfall indicators (R10mm, R20mm, R25mm) were analyzed. The results show that at most stations in the area in the upcoming period, the total number of days with rainfall of 10, 20 and 25mm will be added (other than Nowshahr station and Ramsar station). Overall, among all the stations studied, Anzali station will experience the largest number of days with heavy rainfall of 10 mm and heavy rainfall of 20 and 25 millimeters.
Mohammad Golshan, Abazar Esmaliouri, Keyvan Khorrami,
Volume 13, Issue 44 (3-2019)
Abstract
Groundwater is of the most reliable sources of water for agriculture and drinking. In coastal areas due to saltwater intrusion, determine the interface between fresh and salt water for residents of these areas is very important. In this study, the characteristics of coastal aquifers West and East Babolsar, using geoelectrical studies and geo-electromagnetic studied that these methods are of the most accurate methods in this field. For this purpose 6 sections in the coastline in this area of study were chosen, in each section 15 study locate with 50 meters away in 500 meters coastal distance than with 100, 200, 300, and 400 meters were selected. In order to determining saltwater interface with geo-electric method was assistance of detection wills. With regard to observation data in many points, the results of study showed that the geo-electromagnetic have high accuracy in compere to geo-electric method. Also the results showed that the interface between saltwater and fresh water in the west Babolsar study sections are more than east Bobosar study sections. Over all, with regard to obtained interface depth the saltwater intrusion in each to region exist and it is necessary to tackle of saltwater intrusion in these areas using of management Practices.
Tayebeh Mesbahzadeh, Maryam Mirakbari, Mohsen Mohseni Saravi, Hasan Khosravi, Ghasem Mortezaii,
Volume 13, Issue 46 (10-2019)
Abstract
Reducing or increasing the climate parameters such as temperature and rainfall as a result of the climate change process, causes a variety of droughts. In this study, the effect of climate change on meteorological drought in Yazd province is investigated. For this purpose, the drought time series were determined in two historical periods (1961-2005) and the future (2017-2100) by SPI and SPEI. Historical data from Yazd's synoptic station and future data were generated by the CanESM2 model under RCP scenarios. Drought characteristics such as severity, duration and frequency were extracted based on run theory in order to compare and evaluate the trend of drought changes. The results showed case study experiences more sever droughts in the future than historical period based on SPI under 3 RCP scenarios while based on SPEI index under RCP2.6 and RCP4.5, the drought characteristics will decrease in the future compared with historical period and under RCP8.5, the severity and duration of the drought will increase. The severity-frequency and duration-frequency curve showed that increasing the return period increases the severity and duration of drought.
Mohammad Hossein Jahangir, Mrs. Mahsa Mousavi,
Volume 14, Issue 48 (3-2020)
Abstract
The permanence of rainfall shortage compared with the long-term average of meteorological droughts, reduces river flow, groundwater level and hydrological droughts. To quantify the drought, several indexes have been defined. In this study, two drought indexes, including standardized precipitation index (SPI) and standardized streamflow index (SSI), were used for meteorological and hydrological drought monitoring. The aim of this study was the monitoring the drought in 5 stations in Tehran province during the period of (1985-2016), determining the most appropriate cumulative distribution function for calculating the SSI drought index and also comparative study of meteorological and hydrological drought indicators in this province. The results show that the most suitable cumulative distribution function at the Darake station is Gen-Loglogestic, at the Firuzkuh and Abali station is Gamma, at the Namrud station is Fatigue life and at the Sharifabad station is Beta. Among the stations with proper functions, Derek with the highest P-value (0.996) and the lowest RMSE (0.916) had the best fit with the Gen-Loglogestic distribution function. Also, the similarity in the process of drought resulting from two different indicators,indicates that the meteorological and hydrological indicators are completely same, in other words, surface water resources in Tehran province are completely influenced by rainfall.
Behrooz Mohseni, Mahmood Habibnejhad, Kaka Shahedi, Abdullah Darzi,
Volume 16, Issue 59 (12-2022)
Abstract
Sustainability of groundwater resources means ensuring the permanent availability of essential groundwater services for a long-time. This research was conducted to investigate the sustainability of groundwater resources in the prohibited plain of Behshahr- Bandar-e-Gaz by using water expoliation and green water scarcity indices. Initially, the green water deficit index was calculated based on the concept of water footprint. The water exploitation index was obtained according to the long-term average of annual fresh water resources based on the components of well and qanat discharge, total recharge and return flow. The indices were calculated for the common cropping pattern of the region (spring wheat and rice) for a 33-year period (1982- 2015). The green water deficit index was 2.68 and 2.54 for spring wheat and rice cropping system, respectively. Also, the water exploitation index was 18 percent and 17.8 percent, respectively. Increase in evapotranspiration under spring wheat cropping reduced soil water content and ultimately led to excessive instability of groundwater resources in the study area. Based on the results, the use of water expoliation index can improve the sustainability of groundwater resources in Behshahr Bandar-e-Gaz plain rather than the green water scarcity index.
Ehsan Zahedi, Dr. Ali Talebi, Dr. Kamran Davari, Dr. Vahid Mousavi,
Volume 17, Issue 61 (9-2023)
Abstract
Evapotranspiration (ET) is one of the most important components of the hydrological cycle and an important factor in determining water demand, its spatial distribution and accurate estimation for many studies such as water balance, crop production simulation, program Irrigation planning and water resources management are very important. Also, using of geostatistical methods is one of the ways to estimate evapotranspiration in places without stations. In this study, SWAT hydrological model was used to simulate evapotranspiration of Samalghan watershed . To evaluate the simulation results, indices R2 , bR2 , NS was used. In the calibration stage, the coefficients of R2, bR2 and NS were equal to 0.74, 0.71 and 0.68, respectively, and in the validation stage, they was equal to 0.69, 0.62 and 0.59. .Then, using the results of spatial analysis of data in this study, the exponantial model was selected as the most appropriate model for zoning due to the lower RMSe value and higher correlation.
Mohammad Saeed Cheldavi, Mohammad Heidarnejad, Aslan Egdarnezhad,
Volume 18, Issue 64 (5-2024)
Abstract
Introduction
Spillways are constructed in a variety of types to discharge excess water and major flood streams to avoid damage to dams. Flowing over spillways dissipates energy; however, the non-dissipated portion of energy leads to bed erosion and holes downstream. Ogee spillways are hydraulic structures that have been of interest to researchers. They were developed first in concrete dams and then in embankment dams. These spillways are actually simple examples of a high roughness coefficient channel, considering the low energy dissipation along its length, in the toe of the dam there is no need to use energy dissipating structures. During the flow passing over the crest of the spillway structure, potential energy is converted to kinetic energy at the toe of the structure.Scouring occurs downstream of the stilling basin, and it is important to evaluate techniques to protect the downstream bed. Scholars have studied parameters influencing scouring downstream of stilling basins in recent decades. They analyzed the scouring mechanism and the effects of the structure shape and sediment particle parameters on the scour size. This study aims to obtain deeper insights into the effects of a gate used over the ogee spillway and scouring in the tailrace wall. Thus, an ogee spillway model was developed, and experiments were designed to test the system.
Materials and Methods
Experiments were designed to evaluate the effects of the gate size in the ogee spillway crest and tailrace scour. A plexiglass-walled flume with a metal bottom from Khuzestan Water and Power Organization was used. It had a length of 7 m, a width of 60 cm, and a height of 50 cm, and a total of 45 tests were performed to evaluate the effects of the gate shape and discharge rate on scouring downstream of the ogee spillway. The flow rate was also measured using a calibrated triangular weir and a manometer installed at the end of the flume. A depth gauge was used to read the water level in the required sections, mounted on the flume. A butterfly valve was used to adjust the input flow rate. Additionally, a triangular weir and a manometer were used to measure the flow rate. The flow rate was also measured using a calibrated triangular weir and a manometer installed at the end of the flume. A depth gauge was used to read the water level in the required sections, mounted on the flume. The model was prepared, and the gate was opened until the flow became steady in 40 min. Then, the scour width and length were measured. Furthermore, in order to achieve the goals of this research, the governing parameters of the hydraulic flow of the weir were first introduced, and then the effective governing parameters in this study were presented using the π (Buckingham) method.
Results and Discussion
For a given gate width, an increase in the gate opening reduced the Ds/Ls ratio; the Ds/Ls ratio reduced by 55% when the gate opening decreased by 500%. In fact, it can be said that with a 1% increase in valve opening, sedimentation decreases by 11.0%. As well, it can be concluded that increasing the valve opening leads to further sedimentation along the length and has less effect at depth. For a given gate opening, an increase in the gate width reduced the Ds/Ls ratio; a 400% increase in the gate width reduced the Ds/Ls ratio by 60%. Furthermore, the effect of H/b on the scour depth (Ds) was studied, and the scour depth increased as the gate width increased; a 400% increase in the gate width led to a 24% increase in the scour depth. The effect of H/b on the scour length (L) was evaluated, and a 400% increase in the gate width increased the scour length by 82%. It can be inferred that a further increase in the gate opening would increase the scour length, while an increase in the discharge reduced the Ds/Ls ratio; the Ds/Ls ratio increased by 15% when the discharge decreased by 50%.
Conclusion
One of the structures that is of great importance in water conveyance is the ogee spillways, which are used in many water conveyance networks. Scouring at the downstream of these structures has led researchers in this study to investigate the effect of dimensions and gate opening levels on the ogee spillway and the amount of sedimentation downstream of this structure. In other words, scouring is one of the problems in water structures that can lead to their destruction and, under the best conditions, can cause an increase in suspended sediments in river flow.This study evaluated the contributions of ogee spillways to scour reduction downstream. By comprehensively reviewing previous studies and conducting dimensional analysis, the dimensionless parameters affecting scouring were identified, and experiments were planned based on them. The results indicated that the scour depth could increase by 55% as the gate opening increased. Moreover, an increase in the gate width decreased the scour depth; a 6.5% increase in the gate width would lead to a 1% in the scour depth. A 400% increase in the gate width increased the scour depth by 82%. Moreover, A 1% rise in the discharge reduced the Ds/Ls ratio by 0.3%. Also, Increasing the width of the valve causes more sedimentation along the length and has less of an effect in depth.
Dr Sina Fard Moradinia, Eng. Ebrahim Bagheri, Dr Rasool Jani, Dr Azadeh Falsafian,
Volume 18, Issue 65 (7-2024)
Abstract
Introduction
Drought, as one of the natural disasters, has significant impacts on the environment. Although its occurrence is inevitable, its negative effects can be mitigated by taking measures. Freshwater groundwater, due to its sustainability and high quality, plays an important role in providing drinking water and socio-economic development, especially in dry and semi-arid regions. In this study, drought in Mahneshan County was investigated using various indices. 30 years of rainfall data from Mahneshan station were analyzed. To investigate climatic drought, the SPI index was used, to determine wet and dry periods, the 5 and 7 year moving averages of annual rainfall were used, and to investigate hydrological drought, well data and the GRI index were used. The findings show that climatic and hydrological droughts have occurred in the Mahneshan region and that there is a significant correlation between the SPI index and groundwater level changes. According to the findings, drought is one of the main challenges in the Mahneshan region. The use of various indices to investigate drought is necessary and its negative effects can be mitigated with proper planning. This study only focuses on a specific region and other factors affecting drought and ways to reduce its effects are not investigated. The aim of this study is to provide an overview of the drought situation in the Mahneshan region and the need to pay attention to this phenomenon in future planning and actions.
Materials and Methods
This study is of an applied nature with a descriptive-analytical approach. To collect data, two methods were used: library studies and field surveys. In the field section, various methods were used, such as questionnaires, interviews, and observations, to collect the opinions and views of the local residents, expert information from specialists, and field surveys of water resources and water transmission systems. To complete the information, inquiries were made from relevant organizations such as the Rural Affairs Deputy and the Rural Water and Sewerage Administration. Also, by visiting the region in the field, information related to water resources, water allocation, and other drought-related matters were collected and analyzed and interpreted using scientific methods. To investigate climatic drought in the region, the Standard Precipitation Index (SPI) was used. This index is calculated using long-term rainfall data (30 years) and can show wet, dry, and normal periods in the region. In addition to the SPI index, the 5 and 7 year moving averages of annual rainfall were also used to determine wet and dry periods. In this method, the average rainfall in a specific period of time (5 or 7 years) is calculated and compared with the long-term average rainfall. To investigate hydrological drought in the region, data from wells with appropriate distribution and long-term data were used. Changes in groundwater level in these wells were calculated by the Groundwater Recharge Index (GRI). The GRI indicates the amount of water entering the groundwater and can be used to assess the status of groundwater resources in the region.
Results and Discussion
Analysis of SPI values at different time scales and 5 and 7 year moving averages of rainfall indicates a significant decrease in rainfall in the Mahneshan region over the past 20 years. This downward trend raises concerns about its negative consequences for water resources, agriculture and other water-dependent sectors in the region.
Analysis of the GRI index on monthly and annual time scales indicates a decline in groundwater levels in the Mahneshan region. This decline has been exacerbated due to the imbalance between recharge and withdrawal from the groundwater table, especially in recent years with consecutive droughts.Overexploitation of groundwater resources has threatened the sustainability of these resources.
Correlation analysis between the SPI and GRI indices indicates a significant correlation between meteorological and hydrological droughts in the Mahneshan region. This correlation is stronger at longer time scales. The findings show that meteorological droughts can lead to hydrological droughts in the region.
Analysis of the relationship between meteorological and hydrological droughts with time lags of one, two and three years shows that there is a significant correlation between these two types of droughts with lags of one and two years. This correlation shows that meteorological droughts with lags of one and two years lead to hydrological droughts in the Mahneshan region.
Conclusion
The Mahneshan region has faced a decline in groundwater levels and frequent and severe droughts over the past two decades. Studies show that:
The average annual decline in groundwater level has varied over the years. This is due to the diversity in formation type, permeability, hydraulic gradient, and the amount of groundwater withdrawal in different regions. In the 20-year period (1375 to 1395), the groundwater level in the Mahneshan region has dropped by an average of 45 cm annually. This indicates the excessive and unsustainable withdrawal of groundwater resources. Repeated droughts have also exacerbated the trend of groundwater decline. In addition to rainfall, other factors such as overexploitation of groundwater resources also affect groundwater decline. A comparison of the SPI (climatic drought) and GRI (groundwater resources) indices shows that there is a significant relationship between these two indices on monthly and annual time scales. This relationship shows that climatic drought, with a 2-year lag, affects groundwater decline in the Mahneshan region. The lag time between climatic drought and groundwater decline can vary in different parts of the basin, depending on the diversity of formation type and geological characteristics and different groundwater withdrawals.
Overall, the results of this study show that the Mahneshan region faces a serious challenge of water scarcity and drought. Overexploitation of groundwater resources and repeated droughts have exacerbated this challenge.
Eng. Erisa Jahangiri, Dr Baharak Motamedvaziri, Dr Hadi Kiadaliri,
Volume 18, Issue 65 (7-2024)
Abstract
Introduction
Today, the phenomenon of climate change is one of the problems that has always received attention in the world. One of the reasons for climate change is the increase of greenhouse gases, which have a significant effect on extreme phenomena. Drought forecasting is one of the management strategies that helps to plan properly for using limited water resources. It is also important to examine drought changes based on climate changes from various aspects; in many long-term plans, it is necessary to develop a vision of the future state of rainfall and drought periods for the region. The SPEI index can calculate drought in different time scales and can also include the effects of temperature changes in drought assessment and be used to monitor current and future climate changes based on climate scenarios. Also, the Standard Precipitation Index (SPI) is one of the most important indicators in drought analysis. This index is known as the most appropriate index for drought analysis due to the simplicity of calculations, the use of available rainfall data, and the ability to calculate for any desired time scale. The recent increase in droughts in the Karun 3 watershed has caused water shortages and economic and social damages. Therefore, investigating the effect of climate change and analyzing the frequency of drought is very important. In line with this goal, in this research, firstly, simulation of rainfall, maximum temperature, and minimum temperature of eight meteorological stations using three climate models EC-EARTH, CNRM-CM5, and GFDL-ESM2M under two release scenarios RCP4.5 and RCP8 5. It was forecated for the period (2055-2030).
Materials and methods
In this research, firstly, the temperature data (maximum and minimum) and precipitation output of EC-EARTH, CNRM-CM5 and GFDL-ESM2M climate models under the CORDEX project for RCP4.5 and RCP8.5 emission scenarios with the help of CMhyd Raz software Scaled and time series of maximum, minimum and precipitation temperatures for eight meteorological stations in the future period (2055-2030) were produced. Then, the temperature and precipitation changes in the future period compared to the base period (1995-2020) were investigated. Finally, the investigation of drought (frequency and continuity) in the future period under two release scenarios of RCP4.5 and RCP8.5 by (SPI) and (SPEI) indicators in three-time scales of three, six, and twelve months using DIP software was performed. To evaluate the efficiency and accuracy of three EC-EARTH, CNRM-CM5, and GFDL-ESM2M general circulation models for simulating climate data, the monthly average of climate variables in the period (1990-2005) obtained from the output of the model was compared with the corresponding observational values. For this purpose, Nash Sutcliffe (NS), bias index and coefficient of determination (R^2) were used.
Results and discussion
The results showed that the maximum temperature increase is related to Shushtar station. In this station, the maximum temperature will increase by 1.46 degrees Celsius in the RCP8.5 emission scenario and one degree Celsius in the RCP4.5 emission scenario compared to the base period. Masjid Sulaiman station has the highest increase in minimum temperature. At this station, the minimum temperature increase under the RCP8.5 release scenario is 2.41 degrees Celsius and under the RCP4.5 scenario, it is 1.92 degrees Celsius. Also, the rainfall in the whole range has been decreasing in the coming period. The decrease of rainfall in Kohrang in the RCP8.5 scenario is 146.3 mm and in the RCP4.5 scenario, it is 53.6 mm, which is about 11.7 and 4.3 percent, respectively. In terms of the frequency of drought in the statistical period (2055-2030) on a three-month scale, in the RCP4.5 scenario, Izeh station has the highest frequency with 14 droughts, on a six-month scale, in the RCP4.5 scenario, the maximum number of droughts in Shahrekord with 16 times and on a twelve-month scale, in the RCP4.5 scenario, Kohrang station shows the highest frequency with 15 times. In the RCP8.5 scenario, Izeh station has the highest frequency with 20 drought experiences. Also, in the upcoming period, under the RCP4.5 release scenario, on the scale of three, six, and twelve, respectively, Shahrekord, Yasouj, and Lordegan stations will have eight, 11, and 27 months, and in the RCP8.5 scenario, the drought will continue the most at Masjid Sulaiman, Shushtar, and Lordegan, respectively.
Conclusion
The results showed that the annual long-term average of the maximum and minimum temperature in the future period compared to the base period in all eight stations had an upward trend. Also, the results showed that the maximum temperature under the 8.5RCP scenario increases more than the 4.5RCP release scenario. Also, the results showed that the Kohrang station affected by climate change will have the largest decrease in rainfall in the study area during the coming period. Also, the results showed that in all three-time scales of three, six, and 12 months in the future period, compared to the base period, there are many fluctuations in the time series of SPI and SPEI drought indices. Also, extreme drought conditions will increase in the coming period. It is expected that in the coming period, the number of dry months will be less than the number of months with normal and wet conditions. Also, when examining the drought situation using the SPEI index, it can be seen that, like the SPI index, the pattern of changes in the drought period can be recognized in the stations. It should be mentioned that the intensity of droughts calculated using the SPEI index is rarely higher than the numerical value of two. By comparing the duration and frequency of drought in the studied stations and in different time comparisons, it was found that the SPI index shows the continuity and frequency of drought in most cases compared to the SPEI index.
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