Study of Rainfall Trend and the Volume of Groundwater in Marivan Plain using Geographic Information Systems

Great progress and development in geographic information systems technology has provided users the ability to use this discipline to evaluate changes resulting from natural and human factors, and to determine these changes. In this research, the changes trend in rainfall in the region of Marivan Plain and groundwater level changes were studied using GIS. The geographical coordinates of 23 rain gauges in the GIS were used to produce maps of their distribution using Thiessen polygon method. The study area was delineated from the interpolated map. Monthly precipitation data for a period of 15 years (1997-2011) were obtained from stations in the study area, and the mean precipitation for the area was calculated using the Thiessen polygon method. First, a point map was created using 23 rain gauge station coordinates of the plain, which was then interpolated using the nearest point method. The slope of the regression line reveals increase in rainfall amount during the year of study. Fluctuation of ground water table was studied for the years 1997-2011. Using coordinates of 27 wells dug in the study area, a point map was created. Average yearly groundwater table data related to observational wells in 1997 and 2011 were used to interpolate the point map using the moving average method. The results revealed 2509316 m3 declines in volume of the water.