1010
November 2014
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
biogeochemical cycling of methane and carbon
dioxide, habitat diversity, hydrologic cycles and their
influence on human disease and livelihoods support
systems through controls on fisheries productivity,
water availability and flood recession agriculture
(Appleton et al., 2008). While the interaction
between precipitation, drought, fire, and grazing on
arid environments has been a subject of considerable
research, less is known about the impact of flooding,
or the lack of flooding in flood-adapted ecosystems,
and how it interacts with other factors in modifying
vegetation structure and driving landscape dynamics
(Westbrooke and Florentine, 2005). Monitoring
surface water resources using satellite imagery
is an increasingly important tool for prediction of
floods and droughts (All and Yool, 2004). Vegetation
indices, such as the ones we utilized in this instance
to study flooding regime changes – the normalized
different vegetation index (NDVI) and enhanced
vegetation index (EVI) – represent continuous
variables related to spatially and temporally variable
land productivity or vegetation biomass and have a
very distinct spectral signature for water as opposed
to land.
As a first step towards understanding the relative
importance of different drivers of change in vegetation
dynamic, we asked what the intra-annual timing and
spatial distribution of inundation in the CRB is relative to
the distribution of regional precipitation and discharge in
the two main contributing rivers (the Zambezi and Kwando
Rivers) and whether we could measure change in inundation
extent over the last three decades? To address these
questions, several techniques and remotely-sensed datasets
were required. These included drainage delineation, various
image thresholding techniques performed on Advanced Very
High Resolution Radiometer (AVHRR) NDVI and Moderate-
Resolution Imaging Spectroradiometer (MODIS) EVI data
at 10-day resolution from 1985 to 2010, training samples
collected during 2007, 2009 and 2014 (Figure 5), and various
other hydrologic, climatologic and ancillary geospatial
datasets for the larger Zambezi watershed (see Pricope 2013
for complete details on methods).
The remotely-sensed data, aided by meteorological and
hydrological analyses, have allowed us to establish the intra-
annual flooding regime in the system (Figure 6). The Zambezi
River pushes various amounts of water back into the Chobe,
depending on its discharge while, during secondary flood
pulses, CRB receives water through sporadic connections
from Lake Liambezi and the Lynianti channel, directly fed
by flood waters from the Kwando River making their way
into Mamili Wetlands. Once the peak discharge in the main
trunk of the Zambezi begins to recede, and depending also on
the amount of water being pushed forward from the Kwando
through the Linyanti channel and Lake Liambezi into CRB,
the Chobe then flows forward into the Zambezi, becoming a
tributary. There are other inflows into CRB such as the ones
from the Zambezi Wetlands or from the Kavango River and
Okavango Delta through an ephemeral channel called the
Selinda Spillway. Additionally, our analyses have revealed a
decreasing trend in the extent of flooding from 1985 to 2009 by
approximately 6% and two-week to a one month lag between
the highest discharges in Zambezi River and highest extent
of flooding in Chobe Basin, thus quantifying for the first time
for this system the interconnections between the Chobe and
Zambezi river systems.
While the interaction between
precipitation, drought, fire, and grazing
on arid environments has been a subject
of considerable research, less is known
about the impact of flooding, or the lack
of flooding in flood-adapted ecosystems,
and how it interacts with other factors in
modifying vegetation structure and driving
landscape dynamics.
Figure 5. Training sample data collection during the most recent field season –
marking the edge of the flood in the Zambezi Region of Namibia; pictured, Dr.
Pricope and graduate student Jeri J. Burke (photo by Dr. Andrea Gaughan).
