Using soil-moisture drought indices to evaluate key indicators of agricultural drought in semi-arid Mediterranean Southern Africa

Watson, Andrew B.; Miller, Jodie; Künne, Annika; Kralisch, Sven

doi:10.1016/j.scitotenv.2021.152464

Cited by 31 publications

(50 citation statements)

References 33 publications

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“…IDW is one of the most common interpolation techniques [43], and it performs well for dense precipitation networks [44] and is more suited for discontinuous climate records. Streamflow was likewise temporal data, but was used in the model calibration and validation (except when including reservoir releases; refer to [20]) and was not regionalized. Below, an overview is provided of the climate and streamflow data used for the simulations from 1990 to 2002, as well as the maps of hydrogeology, soil and land use with the model parameters applied to each datatype.…”

Section: The Jams/j2000 Rainfall-runoff Modelmentioning

confidence: 99%

“…Concerns over the dominance of centralized water supply systems [82] have recently been borne out by dry periods between 2015 and 2018 in the WC. Recent applications of drought-related indices, such as the soil moisture deficit index (SMDI) [20] and the standardized precipitation index (SPI) [83] suggest that MAM precipitation has been the main period of meteorological shortfalls, with reductions of between 50 and 70%. Although reductions in JJA precipitation were between 20 and 35% for drought periods, shortfalls in MAM had knock-on effects on streamflow generations in JJA and SON.…”

Section: Hydrological Heterogeneity In Wc and Implications For Sustainabilitymentioning

confidence: 99%

“…The recent Western Cape drought showed signs of hydrological change (2015-2018), where rainfall-runoff modelling was unable to represent these recent conditions [20]. As groundwater levels showed rather abrupt changes as opposed to multi-year drought trends, and widespread groundwater overuse was postulated, the hydrological change thus far has been associated with hydroclimate shortfall and anthropogenic factors.…”

Section: Uncertainties In Modelling Hydrological Changementioning

confidence: 99%

“…However, the dynamic of abrupt water use (over days/months) and slow recharge (sometimes over years) still requires further research. A shift in seasonality could impact hydrological simulations and longer, drier summer conditions have already been detected in the region [20]. Furthermore, a shift in precipitation from mainly winter to all-year precipitation would significantly impact water management, water supply systems and natural vegetation, and also future hydrological simulations in the WC, especially seasonally based parameters (SoilMaxInfSummer and SoilMaxInfWinter).…”

Section: Uncertainties In Modelling Hydrological Changementioning

confidence: 99%

“…The Western Cape (WC) province of South Africa, located within mediterranean southern Africa, has recently experienced a drought (2015-2018), which resulted in reservoir levels dropping to a low of 17% of their full capacity [19]. The drought has highlighted the vulnerability of the centralized water supply systems currently in use in the WC and the need for a consensus on the impact of future climate change [20]. The area lacks the hydrological modelling tools required for climate change-based assessments, as the availability of gauging meteorological and streamflow networks hinders model applications in the WC, as well as in much of southern Africa.…”

Section: Introductionmentioning

confidence: 99%

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Determining Hydrological Variability Using a Multi-Catchment Model Approach for the Western Cape, South Africa

et al. 2021

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Understanding the impacts of climate change requires the development of hydrological modelling tools. However, data scarcity hinders model application, performance, process simulation and uncertainty, especially for Sub-Saharan Africa. In this study, a multi-catchment approach was used to assess hydrological process variability in the Western Cape (WC) of South Africa using the JAMS/J2000 rainfall–runoff model and a Monte Carlo analysis (MCA). Due to much steeper slopes and lower evapotranspiration, the models suggest that WC is dominated by surface runoff from mountainous regions and regional groundwater flow. The results highlight the impact of the catchment size, availability and position of hydroclimatic and anthropogenic factors and the frequency of the signal-to-noise ratio (water balance). For large catchments (>5000 km2), the calibration was able to achieve a Nash–Sutcliffe efficiency (NSE) of 0.61 to 0.88. For small catchments (<2000 km2), NSE was between 0.23 to 0.39. The large catchments had an overall surface runoff, interflow and baseflow contribution of 44, 19 and 37%, respectively, and lower overall uncertainty. The simulated flow components for the small catchments were variable and these results are less certain. The use of a multi-catchment approach allows for identifying the specific factors impacting parameter sensitivities and in turn provides a means to improve hydrological process simulation.

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Section: The Jams/j2000 Rainfall-runoff Modelmentioning

confidence: 99%

Section: Hydrological Heterogeneity In Wc and Implications For Sustainabilitymentioning

confidence: 99%

Section: Uncertainties In Modelling Hydrological Changementioning

confidence: 99%

Section: Uncertainties In Modelling Hydrological Changementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Determining Hydrological Variability Using a Multi-Catchment Model Approach for the Western Cape, South Africa

et al. 2021

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Towards the development of an isotope‐enabled rainfall‐runoff model: Improving the ability to capture hydrological and anthropogenic change

Watson

Vystavna

Kralisch

et al. 2023

Hydrological Processes

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Global hydrological alterations are being driven by climate change. However, while modelling tools have been instrumental in identifying these changes, their calibration is often dependent solely on streamflow data, which limits the ability to simulate important hydrological processes with the required level of certainty. Constraining hydrological process simulations is required to identify robust model parameters, reducing model uncertainty and providing a baseline model for climate‐related risk assessments. In this study, stable isotope measurements of rainwater, groundwater and stream water (δ2H and δ18O), together with an end member mixing analysis (EMMA) (as a post‐processing step) were integrated with the Jena adaptative modelling system (JAMS)/J2000 rainfall‐runoff model, named J2000iso. The J2000iso models of δ2H and δ18O were able to achieve a streamflow Nash–Sutcliffe efficiency (NSE) of 0.75 and 0.72 and an isotope mixing Kling–Gupta efficiency (KGE) of 0.51 and 0.60, respectively. Compared with the base version, the J2000iso had a much smaller variability with 56% less ensemble variance in the NSE, 13% more simulated interflow which resulted in a better soil‐moisture simulation at an observation point, and lower simulated flow component uncertainty. The J2000iso δ2H model was more robust than the base version during a subsequent validation in terms of KGE and Bias with 0.60 and 0.002 compared with 0.51 and −0.14 for the base version. The EMMA provided a means to improve the hydrograph separation ability of the JAMS/J2000. As many catchments around the world are still ungauged and are affected by anthropogenic activities, the development and enhancement of isotope‐enabled modelling provides a means to improve the simulation of key hydrological processes.

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Advancing isotope‐enabled hydrological modelling for ungauged calibration of data‐scarce humid tropical catchments

Watson,

Kralisch,

Miller

et al. 2024

Hydrological Processes

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Realistic projections of the future climate and how this translates to water availability is crucial for sustainable water resource management. However, data availability constrains the capacity to simulate streamflow and corresponding hydrological processes. Developing more robust hydrological models and methods that can circumvent the need for large amounts of hydro‐climatic data is crucial to support water‐related decisions, particularly in developing countries. In this study, we use natural isotope tracers in addition to hydro‐climate data within a newly developed version of the spatially‐distributed J2000iso as an isotope‐enabled rainfall‐runoff model simulating both water and stable isotope (δ2H) fluxes. We pilot the model for the humid tropical San Carlos catchment (2500 km2) in northeastern Costa Rica, which has limited time series, but spatially distributed data. The added benefit of simulating stable isotopes was assessed by comparing different amounts of observation data using three model calibration strategies (i) three streamflow gauges, (ii) three gauges with stream isotopes and (iii) isotopes only. The J2000iso achieved a streamflow Kling–Gupta efficiency (KGE) of 0.55–0.70 across all the models and gauges, but differences in hydrological process simulations emerged when including stable water isotopes in the rainfall‐runoff calibration. Hydrological process simulation varied between the standard J2000 rainfall‐runoff model with a high simulated surface runoff proportion of 37% as opposed to the isotope version with 84%–89% simulated baseflow or interflow. The model solutions that used only isotope data for calibration exhibited differences in simulated interflow, baseflow and model performance but captured bulk water balances with a reasonable match between the simulated and observed hydrographs. We conclude that J2000iso has shown the potential to support water balance modelling for ungauged catchments using stable isotope, satellite and global reanalysis data sets.

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Using soil-moisture drought indices to evaluate key indicators of agricultural drought in semi-arid Mediterranean Southern Africa

Cited by 31 publications

References 33 publications

Determining Hydrological Variability Using a Multi-Catchment Model Approach for the Western Cape, South Africa

Determining Hydrological Variability Using a Multi-Catchment Model Approach for the Western Cape, South Africa

Towards the development of an isotope‐enabled rainfall‐runoff model: Improving the ability to capture hydrological and anthropogenic change

Advancing isotope‐enabled hydrological modelling for ungauged calibration of data‐scarce humid tropical catchments

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