Economic effects of changing the quality and quantity of water in drought conditions, case study: Qazvin, Iran

Drought reduces the quantity and quality of water resources and ultimately increases the risk of agricultural activities at the farm level. Therefore, by developing risk-based economic models, the effects of changes in the quantity and quality of water resources on farmers' decisions should be examined. In this regard, the economic effects of drought on farmers in the Qazvin Plain Irrigation Network have been evaluated. For this purpose, firstly, the river flow quality was simulated using the Qual2k model in 1998–2016 and then using the biophysical model, the effects of water quality on crop yield were estimated. Finally, the risk effects of changes in water quantity and quality were calibrated using a Positive Risk Mathematical Programing. The risky effects of drought are estimated in three scenarios, including increasing salinity of water, reducing the amount of water and a combination of these two. The results showed that farmers' response to changes in water quantity is much greater than its qualitative changes, because the change in water quantity occurs in a shorter time and the cropping pattern leads to the products with less water requirement such as irrigated barley. Also, profit (Gross Margin) and farmer’s income risk declined in all scenarios. Although the negative effects due to reducing the amount of water are more than the effects of increasing the salinity of water, but reducing water quality as a result of drought will have significant effects on the sustainability of agricultural products.