Drought and Ecological Migration in Northwestern of Iran Over the Last Three Decades (1986-2016)

Introduction
Permanent or temporary migration has always been one of the most important strategies adopted by human societies and individuals in the face of ecological or man-made disasters. However, our knowledge about complex relationship between ecological change as cause and migration as effect remains limited. Migration due to drought and climatic change is one of the examples of ecological migration. Drought in Iran is one of the most important climatic hazards as its consequences are evident today in various sectors such as water resources, environment, drying of wetlands and drying of lakes in different parts of country. Monitoring of drought in the past years, can increase our understanding and awareness about climate change and drought and would improve insights, predictions and future planning. Standard Precipitation Index (SPI) is one of the most well-known and widely used index to monitor drought in any scale.
Investigating the relationship between ecological factors and migration would be effective in increasing the understanding of planners and decision makers. Iran internal migration statistics in the last three decades shows that the northwestern counties of the country almost have a negative net migration rate. Therefore, the aim of this paper is to monitor drought and investigate the relationship between drought and internal migration in the northwestern of Iran (Fig.1).
Materials and Methods
In order to achieve the goal of the research, the research process was followed in two separate sections. In the first part, migration studies, raw data of the internal migration matrix in county scale were received from the Statistics Center of Iran. By processing internal migration data, the net migration rate was prepared for each of the counties in the northwestern region of the country. In the drought studies section, initially, representative synoptic stations in the study area were selected. In selecting these stations, having 30 years of continuous statistics and appropriate spatial distribution in the study area was considered. Precipitation data of selected stations were obtained from the Meteorological Organization of Iran and were initially processed. Then SPI index was calculated using Meteorological Drought Monitor (MDM) software. After that, the shapefile of the administrative areas of the study area at the county level was taken from the Ministry of Interior of Iran. Then, the values of the standard precipitation index along with the values of the net migration rate were entered into the GIS environment and attributed to the relevant counties. By using SPI values, the study area was interpolated using thiessen polygons and Inverse Distance Weighting (IDW). Then thiessen polygons were converted to raster format and then the values of each county were calculated using the majority function of the zoning statistics tool.
After this phase, spatial analysis techniques were used to investigate the effect of drought on internal migration in the study area. In this regard, the existence of autocorrelation in dependent and independent variables data were first investigated using the Moran’s I in GIS environment. Since the existence of autocorrelation and clustering pattern was evident in the data, Geographical Weight Regression in GIS environment was used to analyze the relationship between drought and internal migration.

Fig 1. Location of the study area in Iran

Discussion of Results
Drought
Monthly SPI showed that in the past 30 years, the frequency of dry months has been the lowest in the southern areas of Lake Urmia and increased to the central areas, so that the northern part of the region has the highest frequency of dry months. Based on six-month SPI, different pattern of the drought frequencies was seen in the study area. In this regard, Urmia and Miyaneh synoptic stations had the most drought frequencies.
The one-year SPI also showed that Mahabad station and surrounding areas had the lowest drought frequency (2 years). This station had a similar pattern in the monthly and six-month SPI. Among the remaining eleven stations, Ardabil, Khoy, Jolfa, and Tabriz have experienced 6 years of drought and Miyaneh, Mako, Parsabad and Maragheh have experienced 5 years and Khalkhal, Ahar and Urmia have experienced 4 years. One-year SPI revealed that the pattern of drought distribution extends from the southwest, i.e. Mahabad station, to other geographical directions.
Migration
In the last three decades, only 26 percent of the region's counties have had a positive net migration rate. In fact, less than one-third and 74 percent of study area counties have a negative net migration rate. The spatial pattern of distribution of counties with a positive net migration rate is mainly concentrated around Lake Urmia, and this spatial pattern is well visible in the last three decades.
Relationship
The overall results revealed that there is a relatively low coefficient of determination (average 21.5 percent) between the independent and dependent variables. However, this amount of explanatory is not far from expectation because many variables are influential in decisions leading to migration and this amount of explanatory seems to be significant for the drought variable.
Conclusions
Ecological migration is one of the issues that has attracted the attention of various researchers due to the extensive changes in the ecological context that made by humans and sometimes by natural processes. Drought is one of the ecological factors that can cause population movements, especially in arid and semi-arid regions. Although drought is not an unfamiliar phenomenon for arid and semi-arid climates, climate change and excessive use of surface and groundwater resources have intensified its impact. Migration is affected by many factors and understanding drought as one of the migration causes is very complex. The Relationship between drought and migration in the study area indicates a significant but relatively weak relationship. This is primarily due to the nature of migration, which is influenced by various economic, social, cultural, political and environmental factors. Also, drought has several dimensions that in the present study only its climatic dimension has been studied. The SPI revealed that little drought has occurred in the study period. So weak relationship can also be due to the timely distribution of precipitation, as the region has received average precipitation, but this has not happened in the growing season. This adds to the complexity of this relationship. However, the amount obtained R2 is significant given the nature of the migration.