Detection of climate changes by mann-kendall analysis and drought indexes (Case study: Agh Gol wetland)

Introduction:
Climate change is one of the most significant challenges in sustainable development that has negative effects on land and marine ecosystems. This phenomenon leads to imbalances that cause effects including hydrological changes, increased soil erosion, increased runoffs and reduced groundwater aquifer feeding, etc. Effects of climate changes over the past decade have significantly increased in Ecology and Hydrology Literature. Therefore, researches have increased in this area with focusing on climate change. Furthermore, researchers know pressure on wetlands likely due to changes in the hydrological regime directly, and the effects of temperature change and lands-use indirectly. The purpose of this study is to predict climate change important parameters in the study area and management planning of Agh Gol wetland in the predicted conditions to be protected against drought in the coming years. Also, knowing the drought years can provide better and more comprehensive management model for the study area.
 
The study area:
Natural and seasonal Agh Gol wetland is located in 34 degrees and 49 minutes into eastern longitude and 29 degrees and 2 minutes into northern latitude. This wetland that is a Hunting Prohibited Area in Hamedan province in recent years as other water sources was exposed to extra (ecological) pressure of sources, which led to drying up of wetlands in recent years. In this study, we tried to detect the characteristics, climatic and hydrological changes in addition to land-use and factors influencing the revival of the dry wetland and present the strategies affecting the revival of this wetland.
 
Materials & Methods
This study was based on data obtained from synoptic stations of around Agh Gol wetland. To determine the severity of the drought, indices including SPI, RAI, and PNPI were used over the last 30 years.
Also in this study to show the trend of changes and calculation of time series in climatic parameters, Mann-Kendall graphical test was used. In Mann Kendall graphical test each value in the time series, is compared continuously and subsequently with the rest of the series values.
 
Discussion of Results
Kendall graphical test results in Figure (2) shows that with respect to collision of Diagrams u and u' for temperature indicator outside the critical range  a significant trend for the temperature indicator can be recognized in Nozheh Station. Results and the trend of graph changes indicate the occurrence of mutation for temperature indicator in Nozheh station, in the years 2007, 2010, and 2012. Also through 1999, the temperature indicator at the station has shown a positive trend. On the other hand, with the analysis of rainfall indicator at this station the existence of a significant trend in recent years is emphasized and the results indicate observing a mutation in 2013. The rainfall index shows a negative trend at this station and it can be due to reduction of precipitation at the station in recent years.
 
Figure 1. GraphicalKendalltest, Hamedan-Nozhehweather station
 
The results of the analysis of Kendall graph in Weather Station of Hamedan-Airport (Figure 3) in the time period of study (1984-2013) confirm a significant trend for temperature indicator with regard to cross of Line u from the critical point . The results show that in temperature indicator of Hamadan-Airport Station in the years 2008 and 2009 a mutation has occurred that can be a trigger for abrupt climatic change .Changes of Line u in this station has a positive trend considering that this line in the range u> +1.96 has experienced an upward turn and can confirm the existence of time series in Hamedan-Airport station.
 
 
Figure 2. GraphicalKendalltest, Hamadan-airportweather station
 
The results of Mann-Kandall model in weather station of Malayer in the period 1994 to 2013, due to inclusion of Line u for two indicators of temperature and precipitation in the range  and failure to observe the trend due to placement of random series in data of this station does not show a significant trend for these indicators.
 
 
Figure 3. GraphicalKendalltest, Malayer weather station
 
Investigation of drought indices according to Figure 5 represents that based on RAI index in the years 1985, 1990, 1995, 2001, 2008, Hamedan- Airport Station has experienced very dry years and in the rest of the study period, the region has experienced moderate or mild drought.
 
Figure 4.Trends of changes of Drought Indices in Hamadan- Airport weather station
 
Investigating the drought index in Hamedan- Nozheh station showed that for the years 2013, 2012 and 1999, the region has experienced severe dry years according to RAI index. In other years, the region has not been in satisfactory condition, and has experienced years with relative drought.
 
Figure 5. Trends of changes of Drought Indices in Hamadan- Nozheh weather station
 
Evaluating trend of changes of drought in Malayer Station in terms of RAI index showed that in the years 1995, 1997, 1998, 1999 and 2008, the drought index has been in cute conditions. And the rest years of the study period in this station are associated with normal or mildly drought.
 
Figure 6. Trends of changes of Drought Indices in Malayer weather station
Discussion:
The study area around the wetland, over a 30-year study period (1984-2013), according to climatic conditions in meteorological stations did not have stable conditions. Thus, analysis of the climatic results emphasizes that in the years 1999, 2001, 2005, 2008 and recent years (2010- 2013) a significant trend of drought has been experienced in terms of all analyses. The use of drought indices in this study suggests the tensions that region has endured over a period of 30 years. Comparing these results with evaluating the trend of changes and time course of changes and modifications indicated that the greatest changes occurred in the temperature indicator and precipitation variations usually appear with a delay of up to several years after the temperature mutations in the region. Therefore, by a careful planning and consideration of the interests of all concerned and influential parties we can present a comprehensive plan for the sustainable management, and  controlling and mitigating the effects of drought and climate change, in Agh Gol wetland, , to be witness of dewatering of wetlands in the coming years. Also presenting a sustainable agriculture program in accordance with the climatic conditions of the region may contribute to regional stability a lot.