Contents lists available at ScienceDirect Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat Understanding surface water–groundwater interactions for managing large irrigation schemes in the multi-country Fergana valley, Central Asia Mirzakhayot Ibrakhimov a , Usman Khalid Awan b, ⁎ , Biju George b , Umar Waqas Liaqat c a Khorezm Rural Advisory Support Service (KRASS), Urgench, Uzbekistan b International Center for Agricultural Research in the Dry Areas (ICARDA), Cairo, Egypt c Environment and Remote Sensing Laboratory, Department of Water Resources, Graduate School of Water Resources, Sungkyunkwan University, Suwon, 440-746, Republic of Korea ARTICLE INFO Keywords: Groundwater recharge Net groundwater recharge Water balance Crop water requirements ABSTRACT Traditionally, surface water supplies are the sole sources to satisfy crop water requirements in large irrigation schemes such as those in the Fergana Valley, Central Asia. Recent studies indicate that 23–30% of these re- quirements are met from shallow groundwater, but this is not usually quantified. To manage favorable groundwater levels – i.e., without increasing soil salinity and nutrient leaching and reducing crop yields – information on, and quantification of, groundwater recharge and discharge rates at large spatial and temporal scales, as well as understanding their mechanisms of interaction, is indispensable. With the aim to quantify groundwater recharge, discharge and their interaction, a conceptual water balance model at a scale of a Water Consumers’ Association was established on a monthly basis for a 10-year period. Average groundwater recharge was estimated as 780 ± 75.7 mm, representing 62% of surface water supplies. The highest average annual recharge (930 mm) driven by excessive precipitation and water supply was in 2010 and the lowest (667–726 mm) was in years of lower water availability: 2006–2008 and 2012. The net groundwater recharge was 82.4 ± 79 mm, and determined the groundwater level fluctuations. The highest positive net groundwater recharge rate (247 mm) and the shallowest groundwater level (123 cm) also occurred in 2010. The negative net recharge in 2006 (–11 mm), 2008 (–41 mm) and 2012 (–5 mm) indicated deeper groundwater levels during these periods. The groundwater recharge values were excessively high even for this large irrigation scheme. To save limited freshwater resources, groundwater discharge should be reduced, with one option being to reduce ex- cessive drainage outflow. 1. Introduction Groundwater is a critically important global water resource and it is intensively extracted at the rate of 982 km 3 yr -1 (Margat and van der Gun, 2013), of which around 60% is used for agriculture and the rest for domestic and industrial uses (Vrba and van der Gun, 2004). Around 38% of the irrigated areas worldwide have facilities for direct use of groundwater (Siebert et al., 2010). In other areas, capillary rise from shallow groundwater contributes around 20–25% to total crop water requirements (Awan et al., 2014; Ayars et al., 2006; Kahlown et al., 2005; Kazmi et al., 2012). Shallow groundwater within a few cen- timeters of the surface is, however, also a source of waterlogging and secondary soil salinization (Awan et al., 2011a; Kahlown et al., 2005). In many regions (e.g., North Africa, Arabian Peninsula and South Asia), groundwater is intensively extracted at rates that have resulted in de- clines in groundwater levels (Awan and Ismaeel, 2015; George et al., 2011; Venot et al., 2010). In the other areas, the contribution from shallow groundwater to crop water requirements is not accounted for (Awan et al., 2017), leading to freshwater over-supply and eventual waterlogging. Hence, appropriate groundwater management is a pre- requisite for sustainable management of surface and groundwater re- sources in large irrigation schemes. Water from the Amudarya and Syrdarya Rivers is a main source of irrigation in Central Asian countries, and drainage and groundwater serve as a safety net during severe droughts (FAO, 2001). In Central Asia, such as in the Fergana Valley (Karimov et al., 2014) and Khorezm (Awan et al., 2017) Provinces of Uzbekistan, groundwater serves as a storage of water that infiltrates due to excessive water applications in agricultural fields and seepage from earthen irrigation networks. The groundwater level reaches 1–3 m below the land surface during in- tensive irrigation and thus contributes to soil moisture enhancement through capillary rise. Due to uncertainty concerning timely surface https://doi.org/10.1016/j.agwat.2018.01.016 Received 26 September 2016; Received in revised form 11 December 2017; Accepted 15 January 2018 ⁎ Corresponding author. E-mail address: u.k.awan@cgiar.org (U.K. Awan). Agricultural Water Management 201 (2018) 99–106 0378-3774/ © 2018 Elsevier B.V. All rights reserved. T