Climate change, increasing population and changes in land use are all rapidly driving the need to be able to better understand surface water dynamics. The targets set by the United Nations under ...Sustainable Development Goal 6 in relation to freshwater ecosystems also make accurate surface water monitoring increasingly vital. However, the last decades have seen a steady decline in in situ hydrological monitoring and the availability of the growing volume of environmental data from free and open satellite systems is increasingly being recognized as an essential tool for largescale monitoring of water resources. The scientific literature holds many promising studies on satellite-based surface-water mapping, but a systematic evaluation has been lacking. Therefore, a round robin exercise was organized to conduct an intercomparison of 14 different satellite-based approaches for monitoring inland surface dynamics with Sentinel-1, Sentinel-2, and Landsat 8 imagery. The objective was to achieve a better understanding of the pros and cons of different sensors and models for surface water detection and monitoring. Results indicate that, while using a single sensor approach (applying either optical or radar satellite data) can provide comprehensive results for very specific localities, a dual sensor approach (combining data from both optical and radar satellites) is the most effective way to undertake largescale national and regional surface water mapping across bioclimatic gradients.
Display omitted
•Alien tree clearing is predicted to increase mean streamflow by 15.1–29.5%.•Clearing trees in riparian areas had a 1.7x greater impact than terrestrial areas.•Greatest impacts were ...in the mid to low flows, and in dry relative to wet years.•Caused by decreasing transpiration and increasing overland flow and interflow.•Clearing exotic trees from treeless ecosystems may improve water security.
Ecological restoration efforts at scale have been shown to play an important role in reducing human impact on the environment, improving climate change adaptation and halting extinctions globally. Upscaling restoration efforts requires funding, and therefore evidence of the benefits of restoration is needed. This study aims to contribute towards addressing these gaps by: (1) bolstering the evidence base of the water-related impacts of investment into ecological restoration by improving the methods of predicting the streamflow impacts of alien tree clearing; and (2) exploring the potential size of the variability in catchment responses at a fine-scale (60x60m) in one particular region by comparing four different neighbouring catchments. We model the impacts on streamflow in four strategic water providing catchments using the fully-distributed MIKE-SHE modelling tool. We find that the benefits of clearing mature infestations of alien trees, such as pines, from naturally tree-less ecosystems can increase available surface water resources by 15.1 to 29.5%. Clearing riparian invasions is predicted to have a 1.7 times greater impact compared to terrestrial (non-riparian) invasions. The largest modelled impact of restoration on streamflow is on the mid to low flows, and this impact is greater in dry years relative to wet years. The findings are novel in that they shed light on the types of spatial uncertainties that can be expected in modelled gains, with implications for generalisation. These findings are important for leveraging investment to upscale restoration efforts in water scarce regions, as they suggest improved water security during the dry season and droughts. Upscaling efforts is essential if the degradation of ecosystems globally is to be prevented, halted and reversed, as proposed by the United Nations Decade on Ecosystem Restoration.
The social and political transformation that occurred in South Africa has resulted in a new dispensation which requires a paradigm shift in the allocation, management and operation of water ...resources. The mandate is to allocate, manage and operate water resources in order to obtain the optimal balance of equitable, efficient and sustainable water use in catchments. In this paper the concept of Fractional Water Allocation and Capacity Sharing (FWACS) is explored as a method of allocating and managing water entitlements. The concept is introduced for its potential to encourage water market mechanisms while ensuring that social (equity) and sustainability requirements are achieved. The FWACS system is presented as framework in which water use efficiency can be obtained in the context of water scarcity in South Africa as well as many other countries.
More than 50% of South Africa's catchments are deemed to be over-allocated. The challenge is to find ways to bring the over-allocated catchments back into balance in a manner that does not shock the ...socio-economic fabric of the country. The logical starting point is to try to do better with less water. In this article, water conservation and water demand management (WC & WDM) options are discussed, with particular reference to the irrigation sector as it is the dominant water user in South Africa. The concept of banking water, which incentivizes irrigators to become more water use efficient, is also explored.
South Africa experiences some of the lowest water resource system yields in the
world as a result of the high regional variability of rainfall and runoff. Population
growth and economic development ...are placing increasing demands on the nation's
scarce water resources. These factors, combined with some of the objectives of
the new National Water Act (1998), are highlighting the need for efficient
management of South Africa's water resources.
In South Africa's National Water Act (1998) it is stated that its purpose is to ensure
that the nation's water resources are protected, used, conserved, managed and
controlled in a way, which takes into account, inter alia,
i. promoting the efficient, sustainable and beneficial use of water in the public
interest, and
ii. managing floods and droughts.
Efficient and sustainable water resource and risk management can be aided by the
application of runoff forecasting. Forecasting thus fits into the ambit of the National
Water Act and, therefore, there is a need for its operational application to be
investigated. In this document an attempt is made to test the following hypotheses:
Hypothesis 1: Reliable and skilful hydrological forecasts have the ability to prevent
loss of life, spare considerable hardship and save affected
industries and commerce millions of Rands annually if applied
operationally within the context of water resources and risk
management.
Hypothesis 2: Long to medium term rainfall forecasts can be made with a degree
of confidence, and these rainfall forecasts can be converted into
runoff forecasts which, when applied within the framework of water
resources and risk management, are more useful to water resource
managers and users than rainfall forecasts by themselves.
The validity of Hypothesis 1 is investigated by means of a literature review. South
Africa's high climate variability and associated high levels of uncertainty as well as
its current and future water resources situation are reviewed in order to highlight the importance of runoff forecasting in South Africa. Hypothesis 1 is further
examined by reviewing the concepts of hazards and risk with a focus on the role of
effective risk management in preventing human, financial and infrastructural
losses.
A runoff forecasting technique using an indirect methodology, whereby rainfall
forecasts are translated into runoff forecasts, was developed in order to test
Hypothesis 2. The techniques developed are applied using probabilistic regional
rainfall forecasts supplied by the South African Weather Service for 30 day periods
and categorical regional forecasts for one, three and four month periods for
I
regions making up the study area of South Africa, Lesotho and Swaziland. These
forecasts where downscaled spatially for application to the 1946 Quaternary
Catchments making up the study area and temporally to give daily rainfall forecast
values.
Different runoff forecasting time spans produced varying levels of forecast
accuracy and skill, with the three month forecasts producing the worst results,
followed by the four month forecasts. The 30 day and one month forecasts for the
most part produced better results than the more extended forecast periods. In the
study it was found that hydrological forecast accuracy results seem to be inversely
correlated to the amount of rainfall received in a region, i.e. the wetter the region
the less accurate the runoff forecasts. This trend is reflected in both temporal and
spatial patterns where it would seem that variations in the antecedent moisture
conditions in wetter areas and wetter periods contribute to the overall variability,
rendering forecasts less accurate. In general, the runoff forecasts improve with
corresponding improvements in the rainfall forecast accuracy. There are, however,
runoff forecast periods and certain regions that produce poor runoff forecast
results even with improved rainfall forecasts. This would suggest that even perfect
rainfall forecasts still cannot capture all the local scale variability of persistence of
wet and dry days as well as magnitudes of rainfall on individual days and the effect
of catchment antecedent moisture conditions. More local scale rainfall forecasts
are thus still needed in the South African region.
In this particular study the methods used did not produce convincing results in
terms of runoff forecast accuracy and skill scores. The poor performance can
probably be attributed to the relatively unsophisticated nature of the downscaling
and interpolative techniques used to produce daily rainfall forecasts at a
Quaternary Catchment scale. It is the author's opinion that in the near future, with
newly focussed research efforts, and building on what has been learned in this
study, more reliable agrohydrological forecasts can be used within the framework
of water resources and risk management, preventing loss of life, saving
considerable hardship and saving affected industry and commerce millions of
rands annually.
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2002.
PDF