Flood Mapping and Flood Dynamics of the Mekong Delta: ENVISAT-ASAR-WSM Based Time Series Analyses

Abstract

Satellite remote sensing is a valuable tool for monitoring flooding. Microwave sensors are especially appropriate instruments, as they allow the differentiation of inundated from non-inundated areas, regardless of levels of solar illumination or frequency of cloud cover in regions experiencing substantial rainy seasons. In the current study we present the longest synthetic aperture radar-based time series of flood and inundation information derived for the Mekong Delta that has been analyzed for this region so far. We employed overall 60 Envisat ASAR Wide Swath Mode data sets at a spatial resolution of 150 meters acquired during the years 2007-2011 to facilitate a thorough understanding of the flood regime in the Mekong Delta. The Mekong Delta in southern Vietnam comprises 13 provinces and is home to 18 million inhabitants. Extreme dry seasons from late December to May and wet seasons from June to December characterize people's rural life. In this study, we show which areas of the delta are frequently affected by floods and which regions remain dry all year round. Furthermore, we present which areas are flooded at which frequency and elucidate the patterns of flood progression over the course of the rainy season. In this context, we also examine the impact of dykes on floodwater emergence and assess the relationship between retrieved flood occurrence patterns and land use. In addition, the advantages and shortcomings of ENVISAT ASAR-WSM based flood mapping are discussed. The results contribute to a comprehensive understanding of Mekong Delta flood

Mapping Rice Seasonality in the Mekong Delta with Multi-Year Envisat ASAR WSM Data

“…Due to its origin by accumulation of alluvial sediments from the Mekong River, the wide flat plain is mostly located below sea level and consists of fertile soils [61] and, like all deltas, it is vulnerable to a number of factors [62,63]. An intricate flood regime influences it, which used to be a single-peak pulse but is expected to change due to upstream regulatory measures [64,65]. Irrigation and flooding of agricultural land is managed by a dense network of channels, dykes and gates.…”

Has dyke development in the Vietnamese Mekong Delta shifted flood hazard downstream?

“…It accounts for more than 52 % of the national food production and more than 85 % of the annual rice export (GSO, 2015). Being a low-lying coastal region, the VMD is susceptible to both riverine and tidal floods, threatening agricultural production and the safety of people (Schumann et al, 2008;Kuenzer et al, 2013;Le et al, 2007;Dung et al, 2009;Dung et al, 2011;Van et al, 2012). Climate change and sea level rise are expected to increase the risk, not only due to flooding but also due to droughts and salinity intrusion (Wassmann et al, 2004;Khang et al, 2008;Toan, 2014;Hak et al, 2016).…”

Use of Radarsat-2 and Landsat TM Images for Spatial Parameterization of Manning’s Roughness Coefficient in Hydraulic Modeling

“…In essence, these active microwave instruments quantify the apparent roughness of the target surface that is largely defined by the geometry and to lesser extent by the moisture content of the surface. As such, SAR observations have been used in the past for soil moisture monitoring [32,33], flood mapping [34][35][36] and vegetation mapping [37][38][39][40][41][42][43]. The SAR backscatter is controlled by vegetation structure, surface geometry and dielectric properties of the ground targets [44].…”