Effect of hydrology on habitat area in an inland wetland upstream discharge vs extent of greeness in the okavango delta, botswana

Abstract

The annual flood cycle in Botswana's Okavango Delta is a critical factor in the biodiversity and extensive populations of charismatic wildlife, which sustain a thriving tourism industry. Floodwater originates as precipitation hundreds of kilometers away and is subject to natural losses and human diversion in Angola and Namibia before reaching the Delta. However, increasing populations and corresponding agriculture and industry in these countries has put increased pressure on the Delta's limited water resources, necessitating a clear understanding of how streamflow influences ecosystem processes and services. Therefore, I conducted a multi-year analysis of streamflow data from gauges near the upstream entrance and downstream exit of the Delta combined with a remote sensing analysis of four subareas within the Delta to evaluate the relationship between stream flow, and visually evaluated extent of vegetation and normalized vegetation density index (NDVI). NDVI is a common quantitative measure for green vegetation coverage within a landscape which can also be used as an indicator for extent of habitat available to wildlife. NDVI was higher in years with high flows into and out of the delta than in years with low flows. NDVI is more strongly correlated to stream flow out of the Delta than to streamflow into the Delta, suggesting that water available for flooding is a key driver of green vegetative cover and therefore habitat availability for wildlife. My subjective evaluation of imagery found more consistent differences in vegetation extent between high, medium, and low flow years, suggesting that other approaches to quantitative image analysis might show stronger relationships between hydrology and habitat than NDVI.