Abstract
Studying the spatial and temporal distribution of surface water resources is critical, especially in highly populated areas and in regions under climate change pressure. There is an increasing number of satellite Earth observations that can provide information to monitor surface water at global scale. However, mapping surface waters at local and regional scales is still a challenge for numerous reasons (insufficient spatial resolution, vegetation or cloud opacity, limited time-frequency or time-record, information content of the instrument, lack in global retrieval method, interpretability of results, etc.). In this paper, we use 17 years of the MODIS (MODerate-resolution Imaging Spectro-radiometer) observations at a 8-day resolution. This satellite dataset is combined with ground expertise to analyse the evolution of surface waters at the Cambodia/Vietnam border in the Upper Mekong Delta. The trends and evolution of surface waters are very significant and contrasted, illustrating the impact of agriculture practices and dykes construction. In most of the study area in Cambodia. surface water areas show a decreasing trend but with a strong inter-annual variability. In specific areas, an increase of the wet surfaces is even observed. Ground expertise and historical knowledge of the development of the territory enable to link the decrease to ongoing excavation of drainage canals and the increase of deforestation and land reclamation, exposing flooded surfaces previously hidden by vegetation cover. By contrast, in Vietnam, the decreasing trend in wet surfaces is very clear and can be explained by the development of dykes dating back to the 1990s with an acceleration in the late 2000s as part of a national strategy of agriculture intensification. This study shows that coupling satellite data with ground-expertise allows to monitor surface waters at mesoscale (<100 × 100 km2), demonstrating the potential of interdisciplinary approaches for water ressource management and planning.
Highlights
Monitoring the spatial and temporal distribution of surface water resources is critical at the global, national and regional scales
While most papers focus on understanding the impact of upstream water development and dykes construction in the Vietnamese Mekong Delta, we propose to focus and analyse in situ dynamics in the Upper Mekong Delta, a mesoscale region that spreads over Cambodia and Vietnam
In Cambodia, changes detected by visible/infrared observations can be misleading because some of them are related to deforestation and land reclamation instead of a change in water presence
Summary
Monitoring the spatial and temporal distribution of surface water resources is critical at the global, national and regional scales. The Mekong Delta region covers only 12% of Vietnam but produces 50% of the rice produced in the country (with two or three harvests per year depending on the provinces), supports 50% of the fisheries of the country, and 70% of its fruit production [1] This environment has witnessed major changes due to large scale human interventions, for example, the construction of a very dense network of canals, roads, and dykes (see Reference [2,3] for a description of water control infrastructure development in the Vietnamese Mekong Delta). Agriculture practices have evolved, and the construction of high dykes in Vietnam has caused considerable changes in the hydrodynamics of the Mekong River (see for instance References [4,5,6])
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