Integrated assessment of the impact of drought and land use changes on Ground Water (case study: Hamadan-Bahar watershed)

Groundwater drought denotes the condition and hazard during a prolonged meteorological drought when groundwater resources decline and become unavailable or inaccessible for human use. The aim of this study is to identify the influencial factors on groundwater drought in Hamadan- Bahar Watershed,Iran, to understand the forcing mechanisms. The Standardised Precipitation Index (SPI) has been used to quantify the evaluation of meteorological to drought effects in the reduction of ground water table. The influence of land use patterns on the groundwater table drought also has been identified using remote sensing teqnique. The results show that in recent decades ground water table trend has been negative, water table has fallen around 17.91 meters in time period of 1992-2011, that its annual average is equal 0.90 meters. Also, result shows that drought intensity is more severe during the dry years. The rainfall deficit has a significant effect on meteorological drought which has a direct relation with groundwater drought. According to the result can be found in years that severe drought occurred (1996-97, 1998-99, and 2007-2008), the level of ground water in the plain has been decreased severely(1996-97, 1998-99, and 2007-2008). In subsequent years, despite the increase in rainfall in the region, and although the SPI showed the reduced drought situation but groundwater levels has been declining. The main reason is the excessive use of groundwater, in particular, by agriculture Wells. The results of monitoring of land use change indicate an increase in the area of irrigated agriculture, 39.1 km2, in 2011 Compared with 1992. Overexploitation of groundwater for irrigation agriculture and recurrent meteorological droughts are the main causes of groundwater drought in the study area. Efficient irrigation management is essential to reduce the growing pressure on groundwater resources and ensure sustainable water management