Usman Khalid Awan, Bernhard Tischbein:
Linking Farmers Perceptions and Technical Solutions for Groundwater Management in Lower Amu Darya Basin, Uzbekistan

USMAN KHALID AWAN, BERNHARD TISCHBEIN
University of Bonn, Center for Development Research (ZEF), Germany

Due to arid climate, irrigated agriculture in Khorezm region of Uzbekistan depends on water withdrawal from Amu Darya River. Along with irrigation water supplies in vegetation season (April-October), farmers apply ca. 5000 m³ ha^-1 of water for leaching (February to March) the salts in the root zone. Effectiveness of leaching is questioned in past studies as leaching raises the groundwater (GW) level from 2.5m to 0.8m which caused secondary salinity. Farmers believe that they need to fill GW aquifer before the vegetation season so that crops can acquire in-situ crop water demands via capillary rise. Due to intensified irrigation in upstream parts of the Amu Darya basin, water availability in Khorezm is expected to become more limited. In discussion, one option to cope with this situation is raising currently low irrigation efficiency as promising strategy. As this strategy will lead to lower GW, the impacts on the current irrigation strategies partly relying on shallow GW, need to be assessed. Objective of this study was to estimate the reduction in in"=situ crop water demands due to decline in GW levels in Shomakhulum water user association (WUA). Four scenarios (S-A: business"=as-usual, S-B: improved conveyance efficiency, S-C: increased application efficiency, and S-D: improved conveyance and application efficiency) were developed. The impact of scenarios on GW levels was simulated by FEFLOW-3D model. Results showed that improving the irrigation efficiency would lower the GW levels by 12cm in S-B, 38cm in S-C and 44cm in S-D. HYDRUS-1D model was applied to simulate capillary rise contribution for the resulted GW levels. The maximum capillary rise contribution (19%) to the average evapotranspiration of all crops in WUA was for S-A, which reduced to 17, 11 and 9% for S-B, S-C and S-D, respectively. This implies that farmers perception that decline in GW level would affect the in"=situ crop water demand is truthful; hence contribution from GW is a viable strategy for crop production in Khorezm. Therefore, before implementing any irrigation and drainage interventions in the region, water managers needs to consider the in"=situ farmers benefits.

Keywords: Capillary rise, drainage, irrigation, shallow groundwater

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Contact Address: Usman Khalid Awan, University of Bonn, Center for Development Research (ZEF)Bonn, Germany, e-mail: ukawanuni-bonn.de