Abstract
This study used long-term water systems modelling to understand the consequences of major stressors on the water budget of the Amman-Zarqa Basin, Jordan.The first modelling step was to provide an understanding of rainfall patterns and consequently streamflows in the surface water system. Using a 35 year daily time-step dataset of hydro-climatological conditions in the Amman-Zarqa River Basin, the rainfall-runoff relationships were identified. The software “Source” was used to run two hydrological models; GR4J and AWBM, and the models parameterized and calibrated against the long-run recorded flows at the Jerash flow site on the Zarqa River. Models performance was optimised through testing a range of formula adjustments, and modifications of geospatial and temporal inputs. The outputs showed both models performed well in simulating the observed mean flow of the Zarqa River. Long-term (1970-2005) modelled mean flow was 2.33 m3/s (GR4J) and 2.34 m3/s (AWBM), compared to the observed mean of 2.36 m3/s. Model fit was generally good with correlation coefficients of 0.9 (AWBM) and 0.7 (GR4J) for the overall distribution of flow volumes. A critical outcome of the modelling was the identification of inflows from sources other than rainfall. Waste Water Treatment Plant (WWTP) effluent was a substantive inflows (30%-80% steadily increasing from 1989 until 2005) to the Zarqa River. The derived metaparameter sets gave an explanation of some of the basin’s physical properties suggesting large evaporative losses from the basin consistent with the low-flow characterization of the Zarqa River. The variability in the generated flows was also consistent with rainfall variability between sub-catchments.
The second modelling step was to utilize climate projections to estimate water availability between 2022 and 2057. To avoid large uncertainty in the evaluation of hydrologic fluxes, run-off was modelled for the closest future water years (2022-2057) to the observations (1970-2005). Monthly temperature, precipitation and evapotranspiration projections were obtained from the CCSM4, CMIP5 multi-mean, CSIRO-Mk3, GFDL-ESM, and MIROC-ESM2M global circulation models (GCMs) under a range of possible emissions futures (RCPs): RCP26, RCP45, RCP60, RCP85. The monthly projections were downscaled to daily time-series for precipitation and temperature data, from which was derived daily evapotranspiration. The “Delta change method” was used for downscaling to allow future daily projections of any variable as “signal to noise”, maintaining the temporal structure of a changing climate. The results revealed that the basin is only capable of generating runoff through continuous rainfall inputs during winter time. Decreases in runoff including peaks and low flows are predicted over time for both hydrologic models by all GCMs under all RCPs, for example, streamflow in the Zarqa River is predicted to decline by more than 25%. There was variation in the runoff projections between RCP scenarios among the five GCMs as well as between the hydrological models, but there was greater divergence between the GCM models than the RCPs scenarios. Differences between the two hydrologic models might be due to differences in the number of stores between the two hydrological components. Spatial variation in the generated runoff per each sub-catchment was predicted, but an overall 11% reduction over 2022-2057 indicates strong support for predictions of less available surface water.
The third modelling step was to address the consequences that arise from over-abstraction of groundwater, through analysing spatial and temporal changes in standing groundwater levels from 83 monitoring stations in the Amman-Zarqa Groundwater Basin. From surface plots of observed groundwater levels, 5 yearly and 10 yearly averages were estimated and changes on 5 yearly intervals determined. Ten yearly averages were visualized using the surface interpolation methods of inverse distance squared weighting (IDW) and ordinary kriging (OK). Logarithmic trends were used to extrapolate future groundwater levels for bores over the next 35 years. The analysis showed that ongoing over-abstraction rates will cause declining groundwater levels in aquifers. A majority of 67% of analysed bores were declining due to three possible causes; over-abstraction (mostly), evaporation in drought conditions, and transient fluxes between aquifers. A rise in groundwater levels in 22% of the analysed bores was consistent with artificial recharge pathways (irrigation and wastewater discharge) rather than natural replenishment from meteoric water. “Heat-map” visualizations for historical decadal averages showed no groundwater recovery and increasing groundwater depletion through time from the north-west to the south-east of the Basin. The projections simulate drawdown of groundwater levels over 69% of the bores of on average -0.51m/yr for the next 35 years, with some sites experiencing drawdown of -3.8m/yr. This study has simulated the future groundwater flows and surface water flows in the Amman-Zarqa Basin under different scenarios of carbon emission and continuous abstraction rates. As demands increase with population increase, the water industry will face more challenges, with water availability decreasing to 50m3/yr per capita in the mid-21st century. This suggests an urgent need for water reform which includes water supply efficiencies, recycling, desalinisation and increased policing of water theft.
| Date of Award | 2018 |
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| Original language | English |
| Supervisor | Jasmyn LYNCH (Supervisor), Bill Maher (Supervisor), Margi Bohm (Supervisor) & Ross THOMPSON (Supervisor) |