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12Policies supporting rice production and investments in water infrastructure enabled 13 intensification and diversification of farming systems in the Vietnamese Mekong Delta (VMD) 14 over the past 20 years. Yet, demands of food security, economic development, and climate 15 change continue to pose diverging and often conflicting challenges for water resources 16 management in the upper, central, and coastal zones of the delta. The major changes effected in 17 the VMD's hydrological regime and land-use patterns are acknowledged in the literature, but few 18 studies have examined the interplay between these dynamics at the delta scale. Based on time-19series maps and statistical data on land-use, flooding, and salinity intrusion, we investigated the 20 interrelations between land-use dynamics and changes in hydrological regime across the VMD in 21 three representative periods. Land-use was found to be highly variable, changing by 14.94% 22 annually between 2001 and 2012. Rice cropping underwent the greatest change, evolving from 23 single cropping of traditional varieties towards double and triple cropping of high-yielding 24 varieties. Aquaculture remained stable after rapid expansion in the 1990s and early 2000s. 25 2Meanwhile, flooding and salinity intrusion were increasingly controlled by hydrological 26 infrastructure erected to supply freshwater for agriculture. Effects of this infrastructure became 27 particularly evident from 2001 to 2012. During this period, spatial and temporal impacts on 28 flooding and salinity intrusion were found, which extended beyond the rice fields to affect 29 adjacent lands and livelihood activities. Unforeseen effects will likely be aggravated by climate 30 change, suggesting a need to rethink the scale of planning towards a more integrated hydrologic 31 approach. 32 Keywords: land-use change, hydrological regime, land-use planning, water resources 33 management, Mekong Delta, Vietnam 34 1. Introduction 35Surface water, including reservoir water and stream flows, is essential for human activities, 36 particularly for agriculture, forestry, and fisheries. Indeed, land-use and water resources are 37 reciprocally related and mutually dependent. Water availability shapes land-use patterns; and the 38 way that land is utilized affects water supplies and quality. As discussed by Calder (2005), 39 afforestation, intensive agriculture, and urbanization have changed hydrological regime, leading 40 to diminished water quality in developing countries. This has contributed to changes in the 41 global hydrological cycle, which in turn are considered a main factor causing erosion and more 42 than half of the world's soil degradation -resulting in reduced agricultural land availability. 43Understanding how changes in land-use interrelate with changes in hydrological regime is 44 therefore crucial, at the global and at the regional level. 45The interplay between land-use patterns and water resources is particularly manifest in large 46 deltas where agriculture is the dominant livelihood....

The recent increase in smallholder irrigation schemes in the Central Rift Valley of Ethiopia has been associated with the overexploitation of water resources, while the economic viability of these schemes has been questioned. This paper assesses water use efficiencies of the Haleku Irrigation Scheme and quantifies improvement scenarios. The viability of these scenarios is discussed, taking into account the socio-economic performance of the Haleku Irrigation Scheme and the nearby Dodicha Irrigation Scheme -that feature similar settings but contrasting socio-economic performance.The irrigation efficiency of Haleku is 35%, but conveyance losses and application efficiencies vary widely across the scheme. Scenario results indicate scope for improvement and reduced water abstraction. Yields and economic returns of irrigated crops were higher in Haleku than in Dodicha, but yields are still lower than attainable yields. Any strategy to increase irrigation efficiency will have to include a programme to improve crop productivity and economic returns.Considering the over-abstraction of water resources, the poor irrigation performance of Haleku and the disappointing socioeconomic performance of both Haleku and Dodicha suggest that policy should focus on improving existing schemes in the Central Rift Valley instead of further developing new ones. Copyright # 2011 John Wiley & Sons, Ltd. RÉ SUMÉ L'augmentation récente des périmètres irrigués à petite échelle dans la vallée centrale du Rift, en É thiopie a été associée à la surexploitation des ressources en eau, tandis que la viabilité économique de ces emménagements a été mise en doute. Cette étude évalue l'efficacité de l'utilisation d'eau du système irrigué de Haleku et quantifie les scénarios d'amélioration. La viabilité de ces scénarios est discutée en tenant compte des performances socio-économiques de l'aménagement de Haleku et de celles du système irrigué de Dodicha. Les deux sont géographiquement proches, présentent des caractéristiques physiques similaires, mais diffèrent par les performances socio-économiques. L'efficacité de l'irrigation de Haleku est de 35%, mais les pertes de transport et efficacité de l'application varient considérablement au sein du périmètre. Les scénarios appliqués indiquent des possibilités d'amélioration et de réduction des prélèvements d'eau. Les rendements et la rentabilité économique des cultures irriguées sont plus élevés à Haleku qu'à Dodicha, mais les rendements sont toujours inférieurs aux rendements réalisables. Toute stratégie visant à accroître l'efficacité d'irrigation devra inclure un programme de l'amélioration de la productivité des cultures et la rentabilité économique.Compte tenu de la surexploitation des ressources en eau, la performance médiocre de l'irrigation à Haleku et la performance décevante socio-économique des deux emménagements Haleku et Dodicha, il est suggéré que la politique devrait se concentrer

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