Investigation of drought time steps and effects of land use changes on quantitative and qualitative water parameters of Plasjan river

Drought refers to the lack of rainfall in the long trun, which is one of the most important natural disasters due to its spatial extent and short-term and long-term economic, social and environmental consequences (Nikbakht and Moradi, 2019). Factors affecting the physical, chemical and microbial properties of surface waters: precipitation, geographical location, climate, geology, industrial activities, domestic wastewater, agriculture, mineral pollutants, etc. can be mentioned (Mishra et al., 2017). In addition to drought, land use changes change the hydrological cycle of the basin and upset the balance between rainfall, evaporation, soil permeability and runoff (Farokhzadeh et al., 2016). Land use is one of the most important factors affecting the quality of surface water resources, especially rivers, as land population changes, land use patterns change. Therefore, runoff from rainfall as well as urban wastewater discharge leads to an increase in the amount of nutrients and other pollutants into rivers and surface water sources (Moradi et al., 2012). Tahiru et al. (2020) investigated the impact of land use change and land cover on water quality in a catchment area in the northern region of Ghana. Their results showed that there is a positive relationship between land use change and land cover and water quality parameters. Soltani-Gerdefaramarzi et al., (2021) investigated the effect of land use on surface water quality under both wet and dry periods in the Godarkhosh watershed. The results showed that barren and residential lands had the greatest impact on surface water quality and rangeland and forest land use showed a negative correlation with water quality parameters. Also, a strong significant relationship was found between water quality parameters and land use in dry years. Lei et al. (2021) investigated the effects of land cover, topography, and soil on water flow quality at multiple and seasonal spatial scales in a German lowland catchment. Overall changes in water quality on larger scales were estimated better in the summer. Due to the location of Iran in the dry land belt, most of its area will experience drought during most days of the year, which will cause changes in water and environmental resources. Biology, economic growth and development, agricultural activities, etc. are essential; on the other hands, land use changes have a significant impact on surface water quality. This effect can improve or reduce the quality of surface water. These changes have a great adverse effect on the environment and water resources, so the control and monitoring of surface water for various uses is necessary to make water of good quality available to the public. One of the main sources of drinking water, agriculture and industry in Isfahan province is the Eskandari watershed and the Plasjan river. Therefore, paying attention to water resources is one of the appropriate and necessary management measures at the level of the entire basin. Therefore, in the current research, land use changes during two periods of drought and drought have been investigated on the quantitative and qualitative parameters of the Plasjan River.