Characterizing floods in the poorly gauged wetlands of the Tana River Delta, Kenya, using a water balance model and satellite data

Abstract

Abstract. Wetlands, such as those of the Tana River Delta in Kenya, are vital but threatened ecosystems. The flooding characteristics of wetlands largely determine their physical, chemical and biological properties, so their quantification is crucial for wetland management. This quantification can be achieved through hydrological modelling. In addition, the analysis of satellite imagery provides essential hydrological data to monitor floods in poorly gauged zones.The objective of this study was to quantify the main water fluxes and flooding characteristics (extent, duration and number of floods) in the poorly gauged Tana River Delta in East Africa during 2002-2011. To do so, we constructed a lumped hydrological model (the Tana Inundation Model, TIM) that was calibrated and validated with MODIS data. Further analysis of the MYD09A1 500 m composite product provided a map of the empirical probability of flooded state. In non-extreme years and for the current topology of the delta, the flood extent exceeded 300 km 2 . Floods over 200 km 2 occurred on average once a year, with a mean duration of 18 days. River discharge from the upper basin counted for over 95 % of the total water inflow. The results are discussed in the light of possible improvements of the models and wetland management issues.This study provides the first known quantification of spatial and temporal flooding characteristics in the Tana River Delta. As such, it is essential for the water and natural resource management of the Tana River basin. The water balance approach was pertinent to the study of this system, for which information on its internal properties and processes is limited. The methodology, a combination of hydrological modelling and flood mapping using MODIS products, should be applicable to other areas, including those for which data are scarce and cloud cover may be high, and where a medium spatial resolution is required.

Coupled Ground- and Space-Based Assessment of Regional Inundation Dynamics to Assess Impact of Local and Upstream Changes on Evaporation in Tropical Wetlands

“…Along with future climate change projections, the above-mentioned modifications have major implications for the flooding characteristics of these wetlands [10,11] with unknown consequences for the future ecosystem's state. Assessing the vulnerability of wetlands to such changes is very difficult, even more where the remoteness results in insufficient ground truthing due to poor or missing gauging stations [10,[12][13][14]. River gauging data do not provide spatial information on the inundation extent in wetlands [15] and evaporation measurements are scarce, which complicates its estimation on a regional scale [16].…”

Surface water monitoring in small water bodies: potential and limits of multi-sensor Landsat time series

“…Low spatial resolution sensors such as MODIS (Moderate Resolution Imaging Spectroradiometer, 250 m) and AVHRR (Advanced Very High Resolution Radiometer, 1.1 km) providing daily coverage of the globe, notably facilitated the assessment and monitoring of large wetlands (Guo et al, 2017) including the Niger Inner Delta (Mahé et al, 2011;Seiler et al, 2009;Ogilvie et al, 2015;Bergé-Nguyen and Crétaux, 2015), the Okavango (Wolski and Murray-Hudson, 2008;Gumbricht et al, 2004), the Tana 20 Delta (Leauthaud et al, 2013) or the Mekong Sakamoto et al, 2007), large rivers such as the Amazon (Martinez and Le Toan, 2007;Alsdorf et al, 2007) and large lakes notably in East Africa (Swenson and Wahr, 2009;Ouma and Tateishi, 2006) and China (Ma et al, 2007;Qi et al, 2009). These sensors have also been used for global assessments (Prigent et al, 2007;Papa et al, 2010;Klein et al, 2015) but their low spatial resolutions remain inadequate for small reservoirs, as a single MODIS pixel corresponds to an area of 6.25 ha.…”

Characteristics and Factors Influencing the Hysteresis of Water Area–Stage Curves for Poyang Lake

“…Two methods widely used to obtain flooded area data are satellite remote sensing and numerical model simulations. Several forms of satellite remote sensing exist (e.g., Synthetic Aperture Radar (SAR) [28], Moderate Resolution Imaging Spectroradiometer (MODIS) [29], etc.). Numerical simulations are efficient and economical tools that generate enough simulated area data of high spatial and temporal frequency [30,31].…”