Analysis of tropical urban aquifers in response to climate change

<p>Urban aquifers represent an undeveloped resource and utilization is also arising as a method to improve storm water management. In dry climate, these aquifers are an alternative water supply source and in tropical climate can mitigate waterlogging and floods. However, sources and pathways of urban groundwater are more numerous and complex than those in rural environments. Furthermore, climate change and more frequent and intense climate extremes increase the variability in precipitation, soil moisture, and surface water. Therefore, a long-term effective urban water management is imperative.</p><p>This study investigates the groundwater in Shenzhen, a major financial and high-tech center in southern China, along the left side of the Zhujiang Estuary (Pearl River Delta). Shenzhen has a population of about 14 million permanent residents and currently has a total water consumption of 2 billion m<sup>3</sup> per annum. Previous research has investigated the hydrogeological setting and groundwater budgets via numerical flow simulations under steady-state conditions. In the present research, a MODFLOW transient model has been constructed to estimate the groundwater budgets in Shenzhen in response to projected climate change.</p><p>Model conditions are varied, considering the typical Representative Concentration Pathway (RCP) scenarios (RCP 2.6, RCP4.5, RCP 6.0 and RCP 8.5) from 2019 to 2049. Simulations are grouped into two numerical analyses. For the first analysis, the rainfall rate decreases by 37.4% (RCP2.6, RCP4.5) together with a sea-level increment of 0.36 m (RCP 4.5); for the second analysis rainfall increases by 11.82% (RCP 6.0, RCP 8.5) and a sea-level increment of 0.5 m (RCP 8.5).</p><p>In the first analysis (RCP 2.6, RCP 4.5) the groundwater budget decreases by approximately 26% within the study domain, and the water table declines from 1 to 26 m. The second analysis shows a 15.48% increase in the groundwater budget, as the water level rises on average from 0.5 to 8 m. Given the sensitivity of the model results to the choice of future climate scenario, this study indicates the importance of accurate climate change predictions to help local authorities better manage water resources in tropical urban aquifers.</p>

Groundwater budget deficit caused by drought and overexploitation

Groundwater is generally influenced by overexploitation and climatic stresses particularly in arid and semi-arid areas of the world. The present research was conducted to identify the relative contribution of drought and overexploitation to groundwater budget deficit in an unconfined aquifer system. In order to simulate groundwater, the simulated recharge from WetSpass-M model was applied in the MODFLOW model along with other required packages. Moreover, the groundwater budget deficit caused by stressors was quantified through the use of calibrated groundwater model predictions. In order to better understand how the stressors affect the groundwater deficit, the aquifer was divided into Clusters 1, 2, and 3. Locally, the results showed that the contribution of stressors to groundwater budget deficit was the highest in Cluster 1 due to the groundwater overexploitation and quick reaction of the groundwater level to the droughts. Overall, this research showed that both drought and overexploitation, with an average of 2.44 and 3.32 million cubic meters, respectively, played a significant role in groundwater storage deficit. Furthermore, the effect of groundwater overexploitation was approximately 36% more than droughts.

NUMERICAL ANALYSIS OF HUMAN PRESSURE ON GROUNDWATER BUDGET IN THE AREA OF THE ŻURAWINIEC PEAT BOG NATURE RESERVE IN POZNAŃ

Growth of a city, which is linked with intensive urban development, systematically affects groundwater recharge by diminishing its rate. Thus, the phenomenon influences groundwater resources in a hydrogeological unit and, in turn, it causes negative environmental consequences which are difficult or even impossible to reverse. This study analyses the effect of urban development on water budget and its impact on the water-dependent ecosystem. In 1959, a peat bog nature reserve – the Żurawiniec Nature Reserve – was established in the north of Poznań, covering an area of ca. 1.5 ha. During many years the area was losing its original character, which resulted in desiccation and complete deterioration of peatland plants. The analysis of water budget reduction was done through the integration of a spatially distributed water balance model and a numerical hydrogeological model. The simulations were based on data collected for the years 1952, 2001 and 2014. The results of simulations emphasize the significant human impact on groundwater budget leading to a continuous groundwater level dropdown, resulting in over 2 m lower groundwater level in year 2001 in relation to year 1952. The main reason for negative repercussion was a constant decrease of groundwater recharge due to urbanization.

Impact of climate change on the groundwater sustainability in the lower Chao Phraya basin, Thailand

This research investigates the impact of climate change on the hydraulic heads of Thailand's Lower Chao Phraya basin. The research also determines the sustainability of groundwater as the result from climate change. In the study, the climatic scenario (IPSL-CM5A-MR) of the Representative Concentration Pathways (RCP) between 2.6, 4.5 and 8.5 were considered, and the simulations were carried out using the three-dimensional groundwater flow model (i.e. MODFLOW-2000) predicting the groundwater behavior between 2017 and 2036. The findings revealed that the impact of climate change on the hydraulic head fluctuation was positively correlated. Specifically, under the IPSL-CM5A-MR RCP 4.5 that has the highest average precipitation, the average hydraulic head increased. In conclusion, the sustainability of groundwater in the Lower Chao Phraya basin was sufficient during the simulated time. However, the groundwater budget was lower than the average groundwater budget during 2009 – 2014 indicating, the groundwater storage was continuously decreased. Specifically, the 2nd, and 3rd (Phra Pradeang and Nakorn Luang) aquifers may be facing the groundwater shortage in the future.

Transboundary aquifer vulnerability to climate change (2014)

Transboundary aquifer vulnerability to climate change is calculated as the extent of expected groundwater budget regime change in response to change in climate. A high vulnerability is indicative of transboundary aquifers actively interacting with streams, atmosphere and/or sea (e.g. coastal aquifers, SIDS, shallow watertable aquifers, karst aquifers). Climate change Groundwater Transboundary Vulnerability