|dc.description.abstract||The world’s freshwater resources are being placed under increasing pressure owing
to growth in population, economic development, improved standards of living,
agricultural intensification (linked mainly to irrigation), pollution and mismanagement
of available freshwater resources. Already, in many parts of the Orange River
Catchment, water availability has reached a critical stage.
It has become increasingly evident that water related problems can no longer be
resolved by water managers alone, owing to the problems becoming more
interconnected with other development related issues, as well as with social,
economic, environmental, legal and political factors. With the advent of climate
change and the likelihood of increases in extreme events, water managers’
awareness of uncertainties and critical reflections on the adequacy of current
management approaches is increasing.
In order to manage water resources effectively a more holistic approach is required
than has hitherto been the case, in which technological, social and economic
development are linked with the protection of natural ecosystems and with
dependable projections of future climatic conditions. To assess the climate risk
connected with rural and urban water management, and to develop adaptive
strategies that can respond to an increasingly variable climate that is projected into
the future and help to reduce adverse impacts, it is necessary to make connections
between climate related hazards, climate forecasts as well as climate change, and
the planning, design, operation, maintenance, and rehabilitation of water related
infrastructure. Therefore, adaptive water resources management (AWRM), which in
essence is “learning by doing”, is believed to be a timely extension of the integrated
water resources management (IWRM) approach as it acknowledges uncertainty and
is flexible in that it allows for the adjustment of actions based on information learned
about the system. Furthermore, it is suggested that climate risk management be
imbedded within the AWRM framework.
The objective of the research presented in this thesis is to develop techniques to
integrate state-of-the-art climate projection scenarios – which forms part of the first
step of the adaptive management cycle – downscaled to the regional/local scale, with
hydro-climatic hazard determination – which forms part of the first step in the risk
management process – in order to simulate projected impacts of climate change on
hydro-climatic hazards in the Orange River Catchment (defined in this study as those
areas of the catchment that exist within South Africa and Lesotho). The techniques
developed and the results presented in this study can be used by decision-makers in
the water sector in order to make informed proactive decisions as a response to
projected future impacts of hydro-climatic hazards – all within a framework of AWRM.
Steps towards fulfilling the above-mentioned objective begins by way of a
comprehensive literature review; firstly of the study area, where it is identified that the
Orange River Catchment is, in hydro-climatic terms, already a high risk environment;
and secondly, of the relevant concepts involved which are, for this specific study,
those pertaining to climate change, and the associated potential hydro-climatic
impacts. These include risk management and its components, in order identify how
hazard identification fits into the broader concept of risk management; and water
resources management practices, in order to place the issues identified above within
the context of AWRM.
This study uses future projections of climate from five General Circulation Models, all
using the SRES A2 emission scenario. By and large, however, where techniques
developed in this study are demonstrated, this is done using the projections from the
ECHAM5/MPI-OM GCM which, relative to the other four available GCMs, is
considered to provide “middle of the road” projections of future climates over
southern Africa. These climate projections are used in conjunction with the locally
developed and widely verified ACRU hydrological model, as well as a newly
developed hydro-climatic database at a finer spatial resolution than was available
before, to make projections regarding the likelihood and severity of hydro-climatic
hazards that may occur in the Orange River Catchment. The impacts of climate
change on hydro-climatic hazards, viz. design rainfalls, design floods, droughts and
sediment yields are investigated, with the results including a quantitative uncertainty
analysis, by way of an index of concurrence from multiple GCM projections, for each
of the respective analyses.
A new methodology for the calculation of short duration (< 24 hour) design rainfalls
from daily GCM rainfall projections is developed in this study. The methodology
utilises an index storm approach and is based on L-moments, allowing for short
duration design rainfalls to be estimated at any location in South Africa for which
daily GCM rainfall projections exist.
The results from the five GCMs used in this study indicate the following possible
impacts of climate change on hydro-climatic hazards in the Orange River Catchment:
· Design rainfalls of both short and long duration are, by and large, projected to
increase by the intermediate future period represented by 2046 - 2065, and
even more so by the more distant future period 2081 - 2100.
· Design floods are, by and large, projected to increase into the intermediate
future, and even more into the more distant future; with these increases being
larger than those projected for design rainfalls.
· Both meteorological and hydrological droughts are projected to decrease, both
in terms of magnitude and frequency, by the period 2046 - 2065, with further
decreases projected for the period 2081 - 2100. Where increases in
meteorological and hydrological droughts are projected to occur, these are
most likely to be in the western, drier regions of the catchment.
· Annual sediment yields, as well as their year-to-year variability, are projected
to increase by the period 2046 - 2065, and even more so by the period 2081 -
2100. These increases are most likely to occur in the higher rainfall, and
especially in the steeper, regions in the east of the catchment.
Additionally, with respect to the above-mentioned hydro-climatic hazards, it was
· The statistic chosen to describe inter-annual variability of hydro-climatic
variables may create different perceptions of the projected future hydroclimatic
environment and, hence, whether or not the water manager would
decide whether adaptive action is necessary to manage future variability.
· There is greater uncertainty amongst the GCMs used in this study when
estimating design events (rainfall and streamflow) for shorter durations and
longer return periods, indicating that GCMs may still be failing to simulate
individual extreme events.
· The spatial distribution of projected changes in meteorological and
hydrological droughts are different, owing to the complexities introduced by
the hydrological system
· Many areas may be exposed to increases in hydrological hazards (i.e.
hydrological drought, floods and/or sediment yields) because, where one
extreme is projected to decrease, one of the others is often projected to
The thesis is concluded with recommendations for future research in the climate
change and hydrological fields, based on the experiences gained in undertaking this