Regional assessment of groundwater recharge in the lower Mekong Basin

Groundwater recharge remains almost totally unknown across the Mekong River Basin, hindering the evaluation of groundwater potential for irrigation. A regional regression model was developed to map groundwater recharge across the Lower Mekong Basin where agricultural water demand is increasing, especially during the dry season. The model was calibrated with baseflow computed with the local-minimum flow separation method applied to streamflow recorded in 65 unregulated sub-catchments since 1951. Our results, in agreement with previous local studies, indicate that spatial variations in groundwater recharge are predominantly controlled by the climate (rainfall and evapotranspiration) while aquifer characteristics seem to play a secondary role at this regional scale. While this analysis suggests large scope for expanding agricultural groundwater use, the map derived from this study provides a simple way to assess the limits of groundwater-fed irrigation development. Further data measurements to capture local variations in hydrogeology will be required to refine the evaluation of recharge rates to support practical implementations

The costs of uncoordinated infrastructure management in multi-reservoir river basins

Though there are surprisingly few estimates of the economic benefits of coordinated infrastructure development and operations in international river basins, there is a widespread belief that improved cooperation is beneficial for managing water scarcity and variability. Hydro-economic optimization models are commonly-used for identifying efficient allocation of water across time and space, but such models typically assume full coordination. In the real world, investment and operational decisions for specific projects are often made without full consideration of potential downstream impacts. This paper describes a tractable methodology for evaluating the economic benefits of infrastructure coordination. We demonstrate its application over a range of water availability scenarios in a catchment of the Mekong located in Lao PDR, the Nam Ngum River Basin. Results from this basin suggest that coordination improves system net benefits from irrigation and hydropower by approximately 3–12% (or US$12-53 million/yr) assuming moderate levels of flood control, and that the magnitude of coordination benefits generally increases with the level of water availability and with inflow variability. Similar analyses would be useful for developing a systematic understanding of the factors that increase the costs of non-cooperation in river basin systems worldwide, and would likely help to improve targeting of efforts to stimulate complicated negotiations over water resources

Long-term change in rainfall distribution in Northeast Thailand: Will cropping systems be able to adapt?

Climate vagaries and the lack of irrigation, frequently combined with coarse-textured sandy and unevenly distributed saline soils, explain low crop yields and the endemic relative poverty of the rural population in Northeast Thailand (NET). Local and regional trends in agriculturally-relevant rainfall variables were investigated using the Mann-Kendall test, modified to account for serial correlation, and applied to 17 stations across NET, and the regional average Kendall's statistic. Limited changes in rainfall frequency, intensity and seasonality are observed at individual stations over the study period (1953–2004). But we found a significant regional trend toward a wetter dry season. Based on an intimate knowledge of the local farming systems, we discuss the cropping systems adaptation to these rainfall changes. If the wetting of the dry season extends in the future, as expected according to most climate projections, households would not find it difficult to adapt, except for the problems caused by temperature rise, mainly due to their renowned adaptive capacity and high mobility that historically produced diverse and resilient rural livelihood systems. (Résumé d'auteur

Techniques de mobilisation des ressources en eau et pratiques d'utilisation en zones arides : bilans, évolutions et perspectives

Comme dans la plupart des régions, les zones arides ont bénéficié de plusieurs vagues d'aménagements hydroagricoles durant la seconde moitié du XX e siècle pour ralentir, stocker et rendre accessibles des écoulements sporadiques et violents peu utilisables par des ouvrages au fil de l'eau. Cette succession d'aménagements superposés est souvent mal valorisée comme le montrent divers bilans réalisés dans des bassins du Centre tunisien et du Nord Mexique où les retenues collinaires favorisent, avant tout, les pertes évaporatoires. Sur la base de ces constats, les gouvernements ont cherché à améliorer la gestion technique des ouvrages en favorisant les transferts d'eau vers les réservoirs souterrains et cherchent à mobiliser les ressources en eau non conventionnelles avec quelques succès, mais seulement dans des situations spécifiques en raison de leurs coûts élevés (désalinisation), d'une difficile acceptation (réutilisation des eaux usées) ou de leur volume peu important (eau atmosphérique). Toutes ces initiatives n'ont pas arrêté la surexploitation des nappes phréatiques, et peu à peu se mettent en place plusieurs initiatives pour diminuer la demande en eau tout en augmentant la production alimentaire. Cette nouvelle politique finance l'installation des techniques d'irrigation économes (aspersion, goutte-à-goutte, polymères gonflants, conduites verticales, etc.) pour remplacer l'irrigation gravitaire majoritairement utilisée. Après quelques années, il faut bien reconnaître que l'impact de ces nouvelles techniques est moins important que prévu soit à cause d'une utilisation inadéquate, soit par le fait de nouveaux comportements qu'elles ont suscités. Actuellement, les pouvoirs publics testent des outils complémentaires économiques et réglementaires pour rendre plus efficaces ces changements techniques