Icing MAR method for semi-arid, highly continental region (An example at Ulaanbaatar city, Mongolia) Narantsogt Nasanbayar 1 , nnasan.4@gmail.com Prof. Dr. Sangi Chuluunhuyag 1 , 1 Environmental Engineering Department, SCEA, MUST Ulaanbaatar, Mongolia chuluunhuyags@yahoo.com Prof. Dr. Nico Goldscheider II , II Institute of Applied Geosciences, KIT Karlsruhe, Germany nico.goldscheider@kit.edu Abstract - Ulaanbaatar, the capital of Mongolia, exhibits dynamic urban and industrial development with rapidly increasing population numbers. Against the background of this situation, water demand is rising continuously, but water availability is comparatively low and less reliable. A groundwater aquifer located near Ulaanbaatar, is the city’s only source of water, with the main watercourse in the vicinity being the Tuul River, fed by precipitation in the nearby Khentii Mountains. For many decades, the water supply of Ulaanbaatar has been exclusively based on the use of groundwater in the Tuul valley, but as the city grows, ensuring water availability to Ulaanbaatar’s population both now and in the future has become a pressing issue. There are two principal hurdles to overcome in addressing this situation. First, due to the winter coldness and absence of precipitation during spring, the Tuul River usually runs dry during these seasons. Observations show that this dry period has been extending in recent years. Second, in parallel with the city’s increasing development, the extended groundwater aquifer is exhibiting a clear decline, with groundwater levels dropping significantly. Therefore, we propose a groundwater management system based on managed aquifer recharge and present a strategy to implement these measures in the Tuul Valley. It consists of an enhancement of natural recharge rates during the summer flood period, an increase of groundwater recharge through melting ice in the river bed, and the construction of underground dams to retain groundwater. Keywords— MAR - Managed Aquifer recharge, FEFLOW simulation, Icing - Aufeis I. INTRODUCTION A. Study area In 2014, the population of Ulaanbaatar, Mongolia’s capital city reached 1.345 million, about 45 percent of Mongolian total population, with the city producing about 65% of its national GDP. Ulaanbaatar’s water supply depends on wholly of groundwater aquifers along the Tuul River valley on the southeastern side of the city. Ulaanbaatar’s water consumption had reached around 100 M.m 3 per a year. Mongolia’s fast- growing economies combined with widespread migration to the capital are putting more and more strain on the groundwater resources in the Tuul River valley. The Tuul River flows through Mongolia’s capital along the borderline of the Siberian Taiga forest and dry steppe lands of central Asia near Ulaanbaatar. The water level of the Tuul River fluctuates according to annual high-flow to low-flow cycles, with its average water flow being 24,94 m 3 /s. It also feeds the aquifer that providing Ulaanbaatar’s water supply. Ulaanbaatar’s water consumption has grown significantly with the increasing economic development experienced over the last 10 years. Groundwater resource issues, including water scarcity and negatively impacted water quality downward of the city have been identified as a major threat through the dry season, when Tuul River dries out. With the city’s water needs increasing while it’s groundwater aquifer and its streamflow shrinks. The recharge capacity of the aquifer is also being increasingly compromised. The advent and duration of the Tuul River’s dryness is coming earlier and lasting longer year to year. B. Climate The climate of the region is extreme, with large fluctuations in daily and annual amplitudes of air temperature and low precipitation. The average annual temperature is minus 3,1 0 С at absolute maximum 39 0 С in July and an absolute minimum of minus 49 0 С in December. Average absolute minimum air temperature is minus 41 0 C. Low winter temperatures in the low cover snow cause permafrost in soil 10-15m thick. [8]. Below are shown recorded extreme climate parameters in the Ulaanbaatar city wetter station. The Ulaanbaatar terminal site is due to evaporation and infiltration the clayey soils are slight to medium heaving soils in seasonal freezing depth. [7]. The duration of the cold period is 187 days with average daily air