AhmadReza Ghasemi; Morteza Moogooei
Abstract
Introduction
Climate change will affect the availability of water resources and the sustainability of their management. The impact of climate change on water resources has caused concerns and serious challenges around the world. Global climate change has decreased water resources in many regions ...
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Introduction
Climate change will affect the availability of water resources and the sustainability of their management. The impact of climate change on water resources has caused concerns and serious challenges around the world. Global climate change has decreased water resources in many regions and especially in arid and semiarid regions such as Iran. Water shortages decrease both agricultural production and food security and can also limit the economic development and ecosystem health. There is also growing evidence that climate change is changing the hydrological cycle.
The province of Chaharmahal-o-Bakhtiariis the main supplier of water for Khuzestan and Isfahan provinces and inter-basin water transfer talks have always been going on for these two provinces. However, there has not been a comprehensive study on the discharge changes in the rivers of this province, nevertheless, we cannot judge the future of water transfer. In Iran, there have been several studies on the seasonal changes in precipitation and other climatic variables, but assessments of river flows are limited. Therefore, the purpose of this research is to document statistically significant trends in seasonal and annual changes in stream flow in the main rivers in Chaharmahal-o-Bakhtiari.
Materialsand Methods
The total monthly and seasonal streamflow time series for the period of 1358–1389 (32 years) corresponding to 12 hydrometric stations across the Chaharmahal-o- Bakhtiari province were obtained from the Chaharmahal-o-Bakhtiari Regional Water Organization. This study is done with the latest data (1389) published by Chaharmahal-o-Bakhtiari Regional Water Organization. At first, the linear trends are determined on annual and seasonal timescales using Mann–Kendall (MK) non-parametric trend tests.The non-parametric Mann-Kendall tests are based on the calculation of Kendall's tau between two samples which is itself based on the ranks with the samples. This test has been widely used to detect trends in series of environmental data, climatic data or hydrological data, because it is less sensitive to the non-normality of the distribution and less affected by extreme values or outliers in the series.Also, the magnitude of trend- if a linear trend is present in a time series- is estimated by using the non-parametric Sen’ estimator test. The Sen’ estimator method is commonly used for calculating the trend slope. Thus, in this study this method is also used to calculate the trend slopes to obtain the extent of trend changes.
A number of methods can be applied to determine change points of a time series. In this study, the change point in the stream flow time series in 12 studied hydrometric stations is identified by Pettitt’s test. This test is a non-parametric approach for detecting change points based on the mann-whitney test. It has been demonstrated that the Pettitt’s test is a useful technique for examining the occurrence of abrupt changes in climatic records.
Results andDiscussion
The results of the non-parametric Mann-Kendall tests (MK) for all studied rivers through the Chaharmahal-o-Bakhtiari province showed a decreasing trend in the stream flow in all 12 hydrometric stations for both seasonal and annual scale. The amount of reduction based on the Sen’ estimator method, varies at different stations and seasons, from 0.8 m3/s to 17 m3/s in Gordbisheh and Beheshtabad, respectively. On seasonal scale, the results indicate a significant reduction in stream flow of all stations in summer, while in winter-except at two stations (Deh- Cheshmh and Soulegan) significant trend was not observed. The results of Pettitt's test also suggest that, the abrupt downward change (statistically significant) in most studied stations occured in the early 1370s. On the other words, in two recent decades a significant decreasing trend in stream flow has occurred in Karoon and Zayandeh Rood Basin. The results also showed that, in addition to the mean of stream flow, the extreme values of stream flow in these rivers also experience a very sharp decrease during the studied period.
Conclusion
Decreasing trend in all studied hydrometric stations through the Chaharmahal-o-Bakhtiari province clearly shows the reduction of water resources in this province and also the reduction of the role of the province in water supply to the country. The abrupt downward change that occurred in the early 1370s in most studied hydrometric stations also shows that the reduction of water production in the province has started from about 20 years ago. Therefore, for any water transfer plan from this province to other regions, the practical principles should be considered. Another important issue that must be considered is that, the water resources in Chaharmahal-o- Bakhtiari province are sharply decreasing and the water plants should not be based on the old information.
AhmadReza Ghasemi; Foruh Sadat Sayedi
Abstract
Wind is one of the main elements in the climate of each region,and its changes can affect phenomena such as dust storms and the severity of evapotranspiration.The declining trends of surface windreported by previous studies are generally small, but it is still important to assess the distribution of ...
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Wind is one of the main elements in the climate of each region,and its changes can affect phenomena such as dust storms and the severity of evapotranspiration.The declining trends of surface windreported by previous studies are generally small, but it is still important to assess the distribution of the trend of wind speed at the continental to global scale in order to betterunderstand the causes of the trend. This research was carried out aiming to predict wind speed in Iran by 2020 with the Holt-Winters model and using data from a 50-year statistical period (1961-2010). The results showed that this model has the ability to predict wind speed in most parts of the country. The values of the coefficient of explanation of this model varied in 34 stations under survey from 0.39 in Abadan to 80.0 in Babolsar, and the error values in most of these stations were acceptable. The results of Kolmogorov-Smirnov test used to evaluate the normalized residuals of model showed that the model residuals are normal in most of the stations that show the suitability of the model to estimate and predict the wind speed in Iran.The results showed that this model has also simulated the wind speed extreme values in most stations as well. The results of the Holt-Winters model to predict wind speed by 2020, indicate that wind speed in the Eastern half of the country as well as the southern slopes of the Alborz, which have dry and semi-arid climates, will increase by 2020, while the Western half, Southwestern and central regions of the country will experience a decreasing trend of wind speed. The maximum amount of wind speed increase will be at Gorgan station by 2020 with a value of 1.8 meters per second, and themaximum rate of wind speed reduction will occur in southwest stations of the country, so that in the Abadan station, wind speed will decrease from 48.6 m / s to 31.8 m / s by 2020.In other words, we can say that the wind speed in most arid and semiarid regions of the country will increasein the future, while moderate and mountainous areas in western parts of the country will experience a decreasing wind speed.