Climate-justified strategies for sustainable urban water supply system: sources diversification in Almaty city, Kazakhstan

Kazakhstan is a country in transition experiencing a rapid urbanization process with the highest rate in Almaty, the former capital of the country and the largest metropolis in the whole region. Over the past ten years, the city area has doubled its size. Being a concentration of economic and political power, Almaty attracts people from rural areas and neighboring states. Uncontrolled migration of the population leads to disproportional development of the city with inequality between the center and the periphery of the city. Rapid economic development and city growth led to increased per-capita water use and overall water demand and put pressure on water infrastructure. Such the foothill areas of Almaty, the southern part of the Nauryzbay, Bostandyk, and Medeu districts are experiencing a shortage of water supply due to low productivity, deterioration, or absence of networks and facilities. The city is located at the foothills of the northern Tien Shan Mountains in the valley of 4 rivers: Big and Small Almatinka, Esentay, and Kargaly. Climate change led to severe changes in Central Asia at high altitudes, including two times higher than the global average temperature rise and rapid glacier retreat. Shrinking glaciers supply ample quantities of water in the form of increased glacial runoff, and reduced glacier volume will ultimately result in a decrease in both glacier-fed and total runoff. There is no reduction in streamflow in any catchment or season in the northern Tien Shan. Instead, there is a positive trend in surface water availability.  At the same time, climate change poses the risk of more prolonged recharge of reservoirs and aquifers and may cause exhaustion of this water source that currently provides 70% of water for the city. Therefore, envisioning a long-term sustainable development perspective for a city, water resource efficiency, and climate change adaptation should be addressed together. Thus, our study suggests for the short term to limit the use of strategic groundwater reserves and diversify the water supply sources with a bigger share of surface water to benefit from the melting glacials. If the water allocation from groundwater reservoirs will be reduced and the aquifers will be recharged the water deficit for the city may be postponed.