Mapping inundation extent, frequency and duration in the Okavango Delta from 2001 to 2012.

By K. Thito, P. Wolski and M. Murray-Hudson • 2016

The frequency and duration of inundation in river systems are important for a variety of applications, such as water resource management, floodplain mapping and habitat restoration. The Okavango Delta, the fifth largest Ramsar site in the world, has experienced a series of large floods since 2007, following the much lower flooding of the 1990s and early 2000s. This study aimed to establish inundation frequency and duration maps of the Okavango Delta for 2001 to 2012 using MOD09Q1 and MOD11A1. An earlier methods paper testing MODIS for flood mapping in the delta showed 99.4% overall accuracy for inundation mapping of the delta, with a kappa coefficient of 80%. A method based on a time-varying threshold derived from bimodal single-band histograms was used to classify the images into inundated and non-inundated areas. The method relies on the difference in reflectance between waterbodies and dry or vegetated soil, with the former having low reflectance and the latter displaying higher reflectance values. The method takes into account seasonal changes in reflectance. Inundation maps showed a gradual decrease in the delta’s maximum annual inundation extent from 2001 to 2003, followed by a gradual increase from 2004 to 2012, with maximum inundation extent during 2010–2012.

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