عنوان مقاله [English]
Assessment of Climate Change Effects on Renewable Surface Water Resources due to 30 Basins in IRIR.
Climate change as one of the most important environmental hazards around the world has led to the emergence of the worst climatic conditions, such as: heat waves, changes in the temporal and spatial distribution of atmospheric dispersal patterns (heavy rainfalls), prolonged periods of droughts, severe floods, severe storms , Dust particles, etc., and has, in recent years, left unhealthy effects on the hydrological cycle and renewable water sources (IPCC, 2016).
According to the IPCC, the global average temperature in 2016 is about 1.3 degrees Celsius more than the recent 100 years because of uprising the greenhouse gas emissions (IPCC 2017). In Iran, during the period from 1970 to 2004, the average annual temperature ranged from 1 to 2 degrees Celsius (IPCC 2014).
Currently, due to rising temperatures and reduced rainfall in recent years, fresh water resources have fallen across the Iranian catchment areas and in some places have led to the drying rivers. In this way, the annual and balance of water supply's with the amount of renewable water has been interacted and has led to increased demand for agricultural, drinking and industrial water in this paper. To query this, 30 watersheds throughout Iran have been selected as a case study with the aiming to assessing the potential impacts of climate change on renewable water sources.
Materials and methods:
In this case study, using the data of 2113 meteorological and 1116 hydrometric stations of the Ministry of Energy and the Meteorological Organization, the values of the time series of rainfall data and the annual volume flow of all rivers in 30 catchments were selected using Excel software from 1968 to 2018. Subsequently, rainfall and runoff data were classified into three statistical periods of 50, 30 and 20 years (respectively from 1968 to 2018, 1968 to 1997, and 1998 to 2018). Finally, using parametric statistical tests T-test and non-parametric Mann-Whitney and Man-Kendall mutation variability in the time series of these periods, at 95% confidence level and 99% confidence level, SPSS software was evaluated and verified.
Results and discussion:
In this research, the results of parametric and nonparametric statistical tests to reveal the mutation and verification of the trend in the long-term variations of rainfall data and annual flow volume of all rivers in 30 catchments are presented in Table 1. In this case study.
Table (1) Statistical values of T-Student, Mann-Whitney and Mann-Kendall tests of rainfall (R) and surface flow (SF) 30 of catchment area Iran.
In this table, the results of T-Student and Mann-Whitney tests at 95% and 99% confidence levels show that significant leakage has occurred in the catchment area of Lake Uremia in reducing rainfall and annual river flow volumes, as well as in basins there is also a significant mutation in rainfall in decreasing and increasing order, respectively. In the other basins of Aras, Tallesh-Anzali, Lahijan-Noor, Harraz-Neka and Atrak, although the Z (R) statistics of the Mann-Whitney test show a negative trend, but Z (R) precipitation is not significant and not confirmed, In comparison with rainfall, annual volume fluxes in these basins are more intrusive and Z (SF) is significant, which is confirmed by the mutation.
According to the results of these tests, across the catchment areas of Hamoun, Serakhs, West Frontier, Karkheh, Dez-Karoun, Maroun Jarrahi and Zohreh, Kol-Mehran and Southern Coastlands, Bandar Abbas-Sedich, Salt Lake, Gavkhoni, Tashk-Bakhtegan, MeHarlow, Siah-kuh and Rigzarin also have a significant mutation in reducing the rainfall and annual volume flow rates, so the Z (R) and Z (SF) statistics of the Man-Whitney test in these basins Is negative and the result of the mutation is confirmed, if the T (R) and T (SF) statistics obtained from the T-test are positive for all of them.
The results of my Kendall test's revelation in Table 1 show that in most of the country's catchment areas from 1968 to 2018, although the process of rainfall variability is more strongly negative, but their U(ti) R statistics are significant be. Therefore, this phenomenon can be related to the possible impacts of climate change. For example, the minimum U(ti) R statistics in the Dez-Karoun basins is -2.81, Maroun Jarrahi -2.18, Karkheh -1.98 and in the western border region is -1.78, with a significant negative trend And the maximum U(ti) R in the Gherahso-Gorgan basin was + 2.70 with a positive and significant trend. In the case of U(ti) SF, the volume of surface Flow of these basins is -3.35, -2.87, -3.07, -4.51 and -3.29, respectively, and has a decreasing and meaningful trend.
Also, according to the results of this test, it can be seen that in all the country's catchment areas, the variability of rainfall and annual volume flows from 1968 to 1997 (the first statistical period selected for 30 years) compared to the time series from 1968 to 2018 (For 50 years), the U(ti) R and U(ti) SF statistic were 95% and 99% confidence levels less than ± 1.96 and ± 2.58, respectively, and were not significant Be These conditions also apply to the rainfall from 1998 to 2018 (the second period of statistical selection). The trend of fluctuation of surface Flow from 1998 to 2018 (for 20 years) has had a relatively moderate decrease compared to the last 50 years, but their U(ti) SF is significant, therefore, the effect of droughts Climate and excessive perceptions for agriculture, drinking and industry in the last decade, which has greatly diminished as a result of river flows.
Assessing the results of the T- Student and Mann-Whitney tests in this study showed that from 1968 to 2018, rainfall and annual flow volumes of all catchment areas across the country had a relatively slow downward trend. Also, according to the results of the Man-Kendall test in the catchments of Dez-Karoun, Karkheh, West border, Lake Uremia, Central plateau, Hamoun and Serakhs, the trend of long-term variability of atmospheric precipitation (except for the Gherahso-Gorgan basin) has been very low. Since From 1998 to 2018 annual precipitation values have declined over the past half century, but U(ti)R are meaningful and, therefore, can be attributed to the certainty of the trend of rainfall variability to the phenomenon of climate change.
What is certain is that the process of variation of surface flow volume in comparison with annual rainfall has very large fluctuations and has a decreasing intensity several times. It seems that rainfall reduction is the cause of the rivers discharge volume, but other factors such as Excessive harvesting in the upper reaches of the catchment areas has always been effective for the use of various sectors, so according to U(ti) SF, they can be attributed to the climatic phenomenon as the definitive causes, therefore, according to the results of my Kendall test The effect of climate change on the reduction of annual yield and the volume of surface Flow of rivers are skeptical.
Keywords: Climate Change, Precipitation, Man-Kendall, Renewable Water Resources.