Water Withdrawal and Climate Change Causing Water Quality Problems along the Zarafshan River (Tajikistan, Uzbekistan)

Abstract

The Zarafshan River is a typical transboundary (Tajikistan/Uzbekistan) river in Central Asia with a large mountainous part of the upper river catchment, covered by snow and ice. These mountains are part of Central Asia’s „water towers“ [1]. The highly dissected mountain relief with its steep slopes, the relatively negligible water retention by thin soils, and weak evaporation due to low temperatures in high mountains, cause a rapid runoff onto the adjacent semi-arid and desert plains, creating a good water supply where little is precipitated [2]. That is why river valleys of the lowland part were and are the main centers of the agricultural and social development in Central Asia. The research presented here provides a detailed overview of the Zarafshan River, the lifeline for more than six million people. The findings are based on field measurements, existing data from the national hydrometeorological services and an extensive literature analysis. They cover the status quo of hydrological characteristics of the Zarafshan as well as water quality parameters. The discharge of the Zarafshan is characterized by a high natural discharge dynamic in the mountainous upper parts and by sizeable anthropogenic water extractions in the lower parts of the catchment, where on average 60.6% of the available water is diverted for irrigation purposes in the Samarkand and Navoi provinces. The water quality is heavily affected by the unsustainable land use and inadequate/missing water purification techniques. The reduced discharge and the return flow of untreated agricultural drainage water lead to a critical pollution of the river in the lower parts of the catchment. Additional sources of pollutants where identified in the Navoi special economic area and the mining industry in the Tajik part of the catchment. The impact of the global climate change and the socioeconomic growth on the water availability and the water demand will aggravate the detected problems and might lead to severe local and transboundary upstream-downstream water conflicts within the next decades.