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Background
2 water balance, changing water supply, to inform catchment and water resource management (Yang et al., 2015). Across Africa there is a lack of good quality long-term hydrological data (Hughes et al., 2015).
Rationale for the study
In many, but not all regions of the world, evapotranspiration (ET) is the dominant output component of the water balance (Beven et al., 2020). An alternative to the EC benchmark method is that of the surface renewal method (SR) (Hu et al., 2018).
Research objectives
The requirement for calibration using the EC method is to account for the misrepresentation of the temperature change in the air parcel observed by the fine wire thermocouple in the SR method (Spano et al., 2000; Mengistu and Savage, 2010). Understand the seasonal evapotranspiration of the brackish canopy that invades after degradation of a natural grassland (Chapter 3).
Research approach
Understand the change in the overall water balance following a transition from a natural grassland vegetation type to an alternative vegetation state following anthropogenic impacts, using the paired catchment approach and monitoring the water balance components (Chapter 4). 9 Figure 1.1: The pyramid structure of the research project, which made it possible to achieve the overall goal and objective.
Effects of variable retrieval and footprint on surface renewal measurements of sensible and latent heat fluxes in cotton. Calibration of the Surface Renewal Method (SR) under different meteorological conditions in an avocado orchard.
Introduction
Due to the simpler nature of the equipment required, SR is a cheaper alternative to EC (Paw U et al. The difference between HSR1 and HEC varies with the height and delay of the sensor used (Spano et al. 2000, Zapata and Martínez-Cobb 2001).
Materials and Methods
- Research site, vegetation and campaigns
- Equipment
- SR theory
- EC Theory
- Data analysis and processing
23 Figure 2.1: The location of the Cathedral Peak research basin and, within it, the location of basin IX. For the winter campaign (Table 2.3), the EC system measured H and LE for 86.7% of the 30-minute unstable periods during the campaign. 55 Figure 3.1: The location of the Cathedral Peak study catchment area III, the focus location for this study.
The watershed reaches an altitude of 1,982 m.a.s.l. Figure 4.2: Extent of the fire in 2019 according to the lower part of catchment IX. 120 Figure 5.3: Placement of appropriate earth covers that were used to form the HRU within the supports.
Results
- SR1 calibration and validation
- Comparison of SR1, SRDT and SR2 with the benchmark EC
- Data availability and performance of EC, SSR1, SRDT and SR2
Discussion
Over drier surfaces H dominates and indicates that the lack of EBC is potentially related to the measurement of LE (Linquist et al. 2015). The summer campaign experienced 15.5 mm of precipitation, which has been discussed as a factor affecting SR measurements (Liu et al. 2013, Hu et al. 2018).
Conclusion
Acknowledgements
A new procedure based on surface renewal analysis to estimate sensible heat flux: a grapevine case study. Surface renewal performance to independently estimate sensible and latent heat fluxes in heterogeneous crop surfaces.
Introduction
A key component of the hydrologic cycle that changes due to land cover change due to degradation is evapotranspiration (ET) (Li et al., 2017). An example of an alternative is the surface restoration (SR) method (Snyder et al., 2008).
Materials and methods
- Research site
- Observation equipment
- Estimation of energy fluxes
- Calculation of ET o and k c
- Data analysis
- Patching missing data
The degraded condition of the catchment has led to the invasion of barracks, which now dominate the catchment. The EasyFlux-DL program was used for EC data collection and processing of the H component measured during the summer and winter campaigns.
Results
- Determination of α for calibration of the SR1 method
- Comparison between EC, SR1 and SRDT methods
- Assessment of seasonality of ET based on H SRDT
In the canopy after the fire, there was also 36.71 MJ m-2 more Rn in the month than in the canopy before the fire. Of the precipitation, ET accounted for 91% in the pre-fire period and 65% in the post-fire period.
Discussion
The dense nature of the fern canopy distinguishes this form of degradation from other types of degradation. In the fall of the pre-fire (drier) period, 61 mm more precipitation fell than in the post-fire period.
Conclusions
Acknowledgements
Effect of height and time lag on the estimation of sensible heat flux over drip irrigated vineyard using the surface renewal (SR) method over distinct phenological stages. Estimation of sensible and latent heat flux from natural sparse vegetation surfaces using surface renewal.
Introduction
An important question surrounding WPE in any landscape is whether it reduces stream flow and groundwater recharge (Archer et al., 2017). WPE further influences soil water through its effects on infiltration (Archer et al., 2017, Qiao et al., 2017).
Material and Methods
- Research site
- Catchment VI: Near-natural grassland
- Catchment IX: Woody encroached grassland
- Soils
- Equipment and processing
The majority of precipitation falls between October and March (Schulze, 1974; Toucher et al., 2016) mainly as thunderstorms (Schulze, 1974). In the middle and bottom of the catchment, 5” Casella Snowdon rain gauges were used and measured weekly (Toucher et al., 2016).
Theory/Calculation
- Water balance method
- Data quality control and patching
These representative kc values were then applied to ETo calculated for periods when data were not available, allowing ET to be estimated for those days. To estimate the soil heat flux (G), the percentage of net radiation (Rn) determined for the winter season when data were available was applied to natural grassland (14.6 %) and woody vegetation (1 %), respectively.
Results
- Recent energy balance
- Evapotranspiration
- Soil water content
- Water balance
The H component is greater within the natural grassland (44 %) compared to the woody vegetation (32 %), as well as the G component within the natural grassland (9 %) compared to the woody vegetation (1. The lowest point profile volumetric soil water content was 19% (Oct. '19) at the start of the rainfall season and was 5% less than observed in the woody incision catchment.
Discussion
The first obvious change in the energy balance between the woody vegetation and the natural grassland is the available energy flux (Rn - G). Under the woody vegetation canopy, G remains about 1% of Rn year-round and is a small component of the energy balance.
Conclusions
Acknowledgements
The importance of management practices such as prescribed burning is clearly essential to the maintenance of the natural grasslands and therefore to maintaining the water supply and ecosystem services in this region. Opinions and conclusions expressed are those of the author(s) and are not necessarily those of NRF or SAEON.
Funding
Hydrological models have been widely used in the research community for the assessment of the effects of land cover change on stream flow (e.g., another aspect considered was the location of the land cover change and its impact. Confirmation of the ability of the ACRU hydrologic model for use in scenario analysis of land cover change within the upper uThukela basin.
Appendix
Introduction
The management of land cover is therefore linked to the provision of water resources (Alvarenga et al., 2016). Observations in small headwater catchments of the upper uThukela have shown that both forms of land cover change change the water balance (Gray et al., 2021a, b, c).
Materials and Methods
- ACRU hydrological model
- Catchment description
- Model configuration and input data sources
- Confirmation of ACRU model results
- Land cover scenarios
The upper reaches of the catchment are on the Lesotho escarpment at a high altitude (3 378 m.a.s.l.) with steep topography. The catchment area drains into Drieldam at a lower altitude (1,134 m.a.s.l.) with flatter terrain. 119 Figure 5.2: The location and layout of the upper uThukela catchment area with climate stations and flow meter thrusters indicated, as well as an illustration of the 39 sub-catchment areas that have been demarcated.
Results
- Confirmation studies
- Bracken invasion scenario results
- Woody encroachment scenario results
The largest reductions in accumulated mean flow were evident during the winter dry season, where eight catchments showed a reduction in flow of more than 10. During the winter dry season, the reduction in flow was evident throughout the basin, including the basin outlet, unlike the mean annual and summer flow.
Discussion
The vegetation parameters used in the ACRU model for the bracken and wood vegetation are derived from in situ ET measurements and thus reflect the higher ET patterns observed for woody vegetation. The significant changes in low tide can be attributed to the fact that the difference in ET between natural grassland vegetation and woody vegetation is greatest during the dry months when the natural grassland of the region is dormant (Gray et al., 2021b) .
Conclusions
SADDIQUE N, MAHMOOD T and BERNHOFER C (2020) Quantifying the impact of land use/land cover change on the water balance in the forested river basin, Pakistan. WARBURTON ML, SCHULZE RE and JEWITT GPW (2012) Hydrological impacts of land use change in three diverse South African catchments.
Appendix
The overall objective of this thesis was to understand the impact of degradation associated with land cover change on the water balance of Northern high elevation mesic grasslands and what this means for the water supply created by the strategic water resources area of South Africa. The overall aim of this thesis was to understand the impact of land cover change-related degradation on the water balance of high-elevation mesic grasslands in the northern Drakensberg and what this means for the water supply generated by this strategic area. (SWSA) of South Africa.
Key conclusions from the study
After establishing the reliability of the SR method, the energy balance and seasonal ET were determined for natural grassland, woody damage and broken vegetation. A water balance analysis of watershed IX impacted by timber showed a reduction in stream flow over time.
Revisiting the aims and objectives
Contributions to new knowledge
It illustrated the impacts of a shift in land cover in both Leucosidea sericea (wood) and Pteridium aquilinum (bracken) on the established streamflow within the upper uThukela catchment and the potential impact this could have within the larger SWSA area of the largest mountain Drakensberg range. It showed the importance of land management in relation to maintaining the natural state of grasslands (using fire as a management tool) within the protected catchments of the upper UThukela catchment for water supply to the lower region.
Management and future research recommendations
- Importance of observation and monitoring to optimise management
- Nexus approach for process understanding and management
- Consideration of uncertainty
- Climate change lens
Currently within the Northern Drakensberg Mountains, the interconnection within this nexus is poorly understood. Consideration should be given to the impact that climate change is likely to have on water resources in the Northern Drakensberg SWSA and is likely to affect current forest encroachment and the invasion of the warbler.
An aspect not considered in this study, but an important part of global change, is that of climate change. It is well known that climate change will affect and change both the spatial and temporal distribution of rainfall worldwide.
