Analysis of Annual Sediment Loads Entering the Klein Estuary Analysis of Fracture Events in the Klein Estuary. The median of the annual number of pulses (top graph) and changes in the mean monthly number of pulses (bottom graph) entering the Klein estuary in the current, intermediate and far future time periods derived from several GCMs.
LIST OF TABLES
1 INTRODUCTION
- Background
- Problem Statement
- Aims and Objectives: Linking Climate Change to Estuarine Responses Through Changes in Freshwater Inflows
- Overview of the Chapters which Follow
In addition to the possible effects of climate change on estuaries, there are also changes in land cover. The first illustrates the effects of climate change on hydrological responses in a number of estuaries around South Africa (cf.
2 CLIMATE CHANGE: A BRIEF OVERVIEW
What is Climate Change?
Research shows small cyclic variations in the Earth's orbit around the sun, the so-called Milankovitch cycles, resulting in small changes in incoming solar radiation (Arnell, 1996; Saunders, 1999; Pittock, 2005). However, since the Industrial Revolution approximately 150 years ago, humans have significantly influenced Earth's climate through the burning of fossil fuels and agricultural activities (Arnell, 1996; Saunders, 1999; Bates et al., 2008).
Why is Rapid Climate Change Occurring?
As a consequence, temperatures may increase as the earth moves closer to the sun, or decrease as the earth moves further away from the sun (Saunders, 1999). In order to reduce the uncertainty surrounding the earth's future climate, a significant research effort is being spent on the improvement and development of complex atmospheric simulation models.
Projecting the Earth’s Future Climates
This implies that a comprehensive event-based flood risk assessment cannot be completed with a high degree of accuracy (Hewitson et al., 2005). Dynamical downscaling involves high spatial resolution regional climate models (RCMs) nested within the programming of GCMs (Hewitson et al., 2005).
3 ESTUARINE ECOSYSTEMS IN A CLIMATE CHANGE CONTEXT
A Brief Introduction to the Functioning of Estuarine Ecosystems
Due to the inability of primary consumers to photosynthesize, the density of these organisms in estuaries is dependent on the availability of primary producers (Kennish, 1986; Scharler et al., 1998). A significant proportion of the energy is therefore not absorbed by the primary consumer, and this can be transferred back to the estuarine energy base in the form of detritus (McLusky, 1981; Kennish, 1986; Scharler et al., 1998; Whitfield and Bate, 2007).
The Importance of Estuaries
Due to the great diversity of flora and fauna in estuaries, these ecosystems attract a large number of bird species (Whitfield, 2001). Fishing contributes the most to the economic value of estuaries (Mander, 2001; Lamberth and Turpie, 2003).
Indicators of Hydrological Alteration with Special Reference to Estuarine Ecosystems
The IHA consists of 67 parameters used in the description of the hydrological regime (Richter et al., 1996; Richter et al., 1997). This defines freshwater and sediment inputs for that month and thereby defines estuarine conditions in that month (Richter et al., 1996; . Richter et al., 1997; Theron, 2007; Van Niekerk, 2007b).
Factors Affecting Flow Regimes into Estuaries
By the middle of this century, daily maximum temperatures in summer are expected to increase by about 1.5 to 2.5 oC along the coast due to the moderating influence of the ocean, and by 3 to 3.5 oC inland (Schulze et al., 2005). ; Schulze, 2010c; Schulze and Kunz, 2010a). By the end of the century, increases of 3 oC to 4.5 oC along the coast and of 4 oC to 6 oC inland could be observed in South Africa (Schulze et al., 2005;
4 SELECTION AND DESCRIPTION OF STUDY SITES
However, as part of the aim of this dissertation is to investigate the potential ecological impacts of climate change on estuarine systems, the current ecological characteristics of estuaries should be included in the selection criteria (see Figure 4.1 and Table 4.1). Information on the characteristics of estuaries and their respective catchments is present in Figures 4.3 to 4.12 and Tables 4.3 to 4.12.
5 METHODOLOGY
Brief Review of the Problem
The reasoning behind using only one watershed for the study of land use impacts on estuaries is due to the significant time and effort required to accurately configure complex watersheds with dams, withdrawals, and returns for the ACRU modeling system. Furthermore, in the case study of the Klein catchment, inflow into that estuary, together with precipitation on and evaporation from the estuary, together with information on breaching of the estuary mouth at threshold volumes, was used in a daily model for the water balance of the estuary to assess the frequency of exceedances under different climate scenarios (see section 5.8). The techniques developed and demonstrated from simulations of streamflow and sediment yields in the ten selected estuaries, but especially for the Klein estuary, can, in the absence of extensive ecological data, be used to provide a basic assessment of the ecological integrity of estuarine ecosystems.
However, before describing the GCMs used in this study, and how the daily climate output from the GCMs was used as input to a daily hydrological model, an overview of how climate data were obtained for simulations of hydrological models. responses under current (i.e. historical) climatic conditions.
Review of Methods to Obtain Climate Data for the Simulation of Hydrological Responses from Quinary Catchments
From the above, historical temperature data for the center of each of the 5 838 Quinary catchments in South Africa were submitted to the Quinary catchment database (Schulze et al., 2010a). Of the 1,061 pilot stations used in this study, 1,023 stations were represented in the baseline climate study (Hewitson et al., 2005). The monthly adjustment factors calculated during the climate baseline study were then applied to the precipitation data generated for each of the corresponding future climate scenarios.
A weighted average of the adjusted temperature values from each of the two selected stations was calculated to represent temperature in each Quinary catchment (Lumsden et al., 2010).
Simulation of the Daily Streamflows and Sediment Yields using the ACRU Model
MUSLE is used in the ACRU model to quantify the effects of the aforementioned variables on sediment yield estimates. To expose the potential effects of current land use on hydrological responses in estuaries, an additional set of simulations was completed in a case study of the Klein watershed, as described in the next sub-section. In Chapter 4 information about the land use, climate and topography of the Klein watershed is given in Table 4.7.
However, the normal configuration of ACRU's hydrologic modeling system does not allow more than one land use per quinar catchment.
Validation of Climate and Streamflow Simulations
The sorted precipitation yields from each of the five GCMs for the current period were then tabulated with the precipitation yield from the historical period. In this subsection, Figure 5.4.2.2 highlights the accuracy of precipitation and sediment yields from three of the ten selected catchments. Based on this validation for each of the 10 selected watersheds, it was assumed that simulations of future periods, i.e.
Average monthly streamflow values for the outlet Quinar of each of the 10 selected catchments were obtained for both the current GCM-derived period and the same historical period.
Statistical Analysis of Streamflows
Part of the output from the ACRU model is in the form of frequency tables, which provide monthly flow statistics for each completed hydrological simulation. Median month-by-month streamflow statistics from the output of the five GCMs were determined for each of the 10 selected catchments for current, intermediate, and distant future time periods. This section describes the method for assessing the possible effects of artificial irrigation on the freshwater supply to the Klein estuary.
The completed simulations provided daily sediment yields from each of the HRUs in the Klein watershed.
Estuarine Water Balance Model
Vevap = volume of water lost as a result of evaporation from the surface of the estuary (m3). Furthermore, a relationship between the volume and area of the Klein estuary was provided by Van Niekerk, (2010b), thus allowing the calculation of the estuary area for a given volume, or vice versa (Figure 5.8.2). Vinput = volume of water received by the estuary on a given day (m3), Ppt = rainfall occurring over the surface of the estuary (mm) Aest = area of the estuary on a given day (m2).
From these equations, it is possible to evaluate the occurrence of breakthrough and closure of the Klein River mouth for different climate scenarios in the Klein River catchment based on the amount of water contained in the river.
6 RESULTS
In the distant future, there is negligible change in average flow from this system (Figure 6.1.1.2, bottom). In the intermediate future, increases in mean, median and low flow are illustrated in Figure 6.1.1.10 (middle). In the distant future, low flows increase during the late fall/early winter period (Figure 6.1.1.10, bottom).
From the intermediate period to the distant future there is a slight decrease in the occurrence of pulses. While increases in flows are predicted for this system (cf. Figure 6.1.1.6), there are only slight increases in the occurrence of impulses in the future. In the distant future period there is a slightly more pronounced increase in the number of pulses.
Results and Discussion 2: A Case Study on Simulated Impacts of Upstream Land Uses and Channel Changes on Hydrological Responses into the Klein River
However, when actual land use (excluding irrigation) is included in these simulations (see Figure 6.2.1.3 middle), the reduction in means becomes much greater. The inclusion of current land use in the simulations shows an increase in the number of pulses when comparing the results of the basic land cover simulations (see Figure 6.2.2.1 middle). This is similar to the results from the baseline land cover simulations (see Figure 6.2.2.1 above).
Under baseline land cover conditions, pulses occur only in the wet winter season for all three climate scenarios (Figure 6.2.2.2 top).
7 DISCUSSION OF RESULTS AND CONCLUSIONS
- Discussion on Regional Differences of Hydrological Responses to Climate Change
- Discussion on Impacts of Land Uses on Hydrological Responses
- Discussion on Ecological Responses to Changes in Freshwater Inflows
- Discussion on Impacts of Changing Sediment Yields into Estuaries
- Discussion on Berm Formation
- Discussion on Estuarine Ecology and Economic Contributions of Estuarine Systems
- Overall Conclusions
This in turn can result in a deficit of the nutrients and chemicals required for primary production (cf. Literature review subsections 3.1.2 and 3.1.4). The resulting isolation of the Klein Estuary from marine influences may result in the system becoming hypo-saline (cf. Literature Review Chapter 3; Results subsection 6.2). In some cases, freshwater inflow may cease, as is expected to occur in the Klein estuary when irrigation routines are included (cf. Results subsection 6.2).
In the eastern regions, the volume of stream flows entering estuaries is expected to increase in the medium and long term.
8 RECOMMENDATIONS FOR FUTURE INVESTIGATIONS
In future research, the selection of estuarine ecosystems should be undertaken using the Principle Component Analysis approach that grouped estuaries by climate scenarios and the associated flow metrics that were likely to affect each estuary most during each climate scenario, based on eigenvectors. With the above improvements, the possible effects of future climate change on river estuaries can be assessed more thoroughly. With this knowledge, conservation strategies regarding estuarine ecosystems (including their upstream catchments) can be developed and implemented.
Therefore, future research in this area could be of utmost importance, as estuaries affect many aspects of South Africa's coastal ecology and economy.
9 REFERENCES
Climate Change and Water Resources in Southern Africa: Studies on Scenarios, Impacts, Vulnerabilities and Adaptation. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. The Thukela Dialogue Managing water-related issues on climate variability and climate change in South Africa.
Summary of results and key findings from the 2010 study on climate change and the agricultural sector in South Africa.
10 APPENDIX A: RELATIVE ERRORS IN GCM OUTPUT COMPARED WITH HISTORICAL DATA FOR THE SAME PERIOD
Historical and simulated current climate scenarios; Baseline land cover, multi-GCM comparison of mean annual precipitation, streamflow, and sediment. Historical and simulated current climate scenarios; Basic ground cover; Comparison of multiple GCM mean annual precipitation, streamflow, and sediment volume.
