Thermal Imagery-Derived Surface Inundation Modeling to Assess Flood Risk in a Flood-Pulsed Savannah Watershed in Botswana and Namibia

Abstract

Abstract:The Chobe River Basin (CRB), a sub-basin of the Upper Zambezi Basin shared by Namibia and Botswana, is a complex hydrologic system that lies at the center of the world's largest transfrontier conservation area. Despite its regional importance for livelihoods and biodiversity, its hydrology, controlled by the timing and relative contributions of water from two regional rivers, remains poorly understood. An increase in the magnitude of flooding in this region since 2009 has resulted in significant displacements of rural communities. We use an innovative approach that employs time-series of thermal imagery and station discharge data to model seasonal flooding patterns, identify the driving forces that control the magnitude of flooding and the high population density areas that are most at risk of high magnitude floods throughout the watershed. Spatio-temporal changes in surface inundation determined using NASA Moderate-resolution Imaging Spectroradiometer (MODIS) thermal imagery (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015) revealed that flooding extent in the CRB is extremely variable, ranging from 401 km 2 to 5779 km 2 over the last 15 years. A multiple regression model of lagged discharge of surface contributor basins and flooding extent in the CRB indicated that the best predictor of flooding in this region is the discharge of the Zambezi River 64 days prior to flooding. The seasonal floods have increased drastically in magnitude since 2008 causing large populations to be displaced. Over 46,000 people (53% of Zambezi Region population) are living in high magnitude flood risk areas, making the need for resettlement planning and mitigation strategies increasingly important.

Hydrometeorology and flood pulse dynamics drive diarrheal disease outbreaks and increase vulnerability to climate change in surface-water-dependent populations: A retrospective analysis

“…Under climate change, rainfall variability is expected to increase across Southern Africa in the 21st century, with a spread in the rainfall probability distribution, increasing the frequency of droughts, extreme rainfall events, and floods in the future [ 55 ]. In flood pulse systems, existing hydrological dynamics already create significant variation in the volume of water flow in river systems and the area of floodplain inundation (401 km 2 to 5,779 km 2 from 2000 to 2015 in the Chobe River system [ 56 ]), with consequent impacts on water quality dynamics and waterborne pathogen exposure. Predicted increases in hydrological extremes associated with climate change will further elevate the vulnerability of populations dependent on surface water resources in these landscapes.…”

Tropical Wetland (TropWet) Mapping Tool: The Automatic Detection of Open and Vegetated Waterbodies in Google Earth Engine for Tropical Wetlands

“…The confluence of the Chobe River and Zambezi at the eastern edge of the Zambezi Region occurs over resistant basalt, resulting in backwater ponding during peak flow conditions [48,49]. The floodplain is dominated by a fine-grained sandy alluvium supporting tall grassland that is seasonally inundated.…”

“…The floodplain is dominated by a fine-grained sandy alluvium supporting tall grassland that is seasonally inundated. The area forms part of the Kavango-Zambezi Transfrontier Conservation Area (KAZA), a globally significant region for biodiversity including a key elephant migration route [49,50]. Flooding in this region is complex, being influenced by a number of different sources including a main flood pulse from the Zambezi River, backing up water into the Chobe system and a secondary flood pulse from the Kwando River via a combination of wetlands, lakes, and channels [50].…”

“…Flooding in this region is complex, being influenced by a number of different sources including a main flood pulse from the Zambezi River, backing up water into the Chobe system and a secondary flood pulse from the Kwando River via a combination of wetlands, lakes, and channels [50]. Apparent climate-change induced circulation pattern changes have resulted in extreme flood events (noticeably in 2009 and 2011) with devastating impacts for local communities [49,51,52]. The Zambezi Region is also a high-risk area for diseases like malaria [53], with transmission peaks timing with floodwater pulses [54].…”

“…The Zambezi Region represents a significant habitat for a number of species including the critically endangered wild dog as well as acting as a vital migration corridor for a range of herbivore species such as elephant [49]. Much of this biodiversity is reliant on the annual pulse of floodwater, originating from the Angolan Highlands.…”