The Relationship between Recent Drought and Groundwater resources in the Qazvin plain. Water is the most precious natural endowment of each region and plays an important role in development of societies. Human factors at one hand, and natural factors at the other hand leads to variation in water resources, that is the basis of life and a main of factor in development of each society as well as the basis of scheduling for different sections at different levels. These variations, specific in arid and semi arid countries, have doubled the problems resulting from limited water resources and are a serious problem for planners. Iran is located on the arid zone of the world and its average of annual precipitation is approximately 250 mm. so, different intensities of drought are a common phenomenon in Iran that causes significant damages every year. For example, in drought of1977‐88, the average of annual precipitation was 26% less than the average of the 30‐year period and also 44% less than the average of previous year, which damaged 70% of dry farming and 10% of irrigated production, and the production of wheat and rise decreased 2400000 and 400000 tons respectively. So, at this project the relationship between variations of water table of Qazvin plain, as a main agricultural, industrial and residential center, and droughts has examined. The recognition of severity drought and relation between both climatic and hydrologic drought have been done by using data set of climatic and hydrometric stations in Qazvin plain. Intensity and longevity of droughts has calculated and examined using common methods and the relationship between groundwater and climatic droughts assessed in terms of these results. Using weighted mean method, the average of annual precipitation of Qazvin plain has calculated as nearly 325mm, which in rainy and rainless years it reaches nearly 580mm and 190mm respectively; in other words, the ratio of rainless year to rainy is 1 to 3 .One of the significant features of Qazvin plain is the presence of two absolutely different period of raining during a year. Correspondence of arid season with the growth period of crops necessitates the consumption of water in order to fulfill the water need of plants, and this is mainly done by exploiting groundwater resources. Productivity of the lands and high reliability coefficient of the groundwater of this plain has led to using deep and shallow wells. During the last 3 decades, the number of these wells has increased quintuple. Increased number of wells and spread of irrigated cultivation in this plain has led to increased exploitation of groundwater resources. Increased exploitation has disorder the balance between input and output resources of the plain and has led to decrease store of water table and negative of water budget. Decreased resources of water represent a completely negative procedure, in which correlation between fall in the water table and time is approximately ‐96%; in other words, a fall of 25cm has occurred every year. Performed studies revealed that during recent 3‐year droughts (1997‐1999), the fall in the water table was about 6m that is a significant and worrying figure. Correlation between the water table and increased number of deep wells shows that for every dugout well, a decrease of 1.6mm has occurred in
ground waters of Qazvin plain. Annual cycle and behavior of groundwater resources of Qazvin plain is affected by cycle and regime of region rain. This influence reveals in a two‐month delay. The highest of water table is seen in June. Decreased rain, as well as, continuous increased number of wells and exploitation of ground waters will lead to an environmental imbalance in Qazvin plain. Given to increased trend of global warming and irrigation requirement of agricultural productions, it is necessary for farmers to use standard and scientific principles for exploiting these resources. Damming around the plain, grow of plants that need less water, using mechanized system of irrigation, changing of life styles and water sublimate are appropriate guidelines for preventing of intensification of water crisis in Qazvin plain. Drought effects on water resources
Sprinkler irrigation