The assessment of the seasonal variability of climate conditions on the variation of groundwater recharge and groundwater levels (GWLs) in different aquifers was analysed for the historical (1986–2005), present (2013–2014), and future (2046–2065) period. In this study, the distributed hydrological model (PANTA RHEI) was coupled with the finite element subsurface flow system model (FEFLOW) to predict the future variation of groundwater resources. The effect of future climate change on groundwater resources was assessed using a modelling approach for a coastal area in Vietnam. Assessment of spatial and temporal variability in the surface water and groundwater isotopic composition within the Cauvery River Basin provides an important dataset for developing a sustainable river water management plan for a tropical mesoscale river system. The base flow contribution is much higher during the pre-monsoon season at higher elevation, thereby playing a crucial role in sustaining stream flow during the dry time. Similarly, the average groundwater contribution to the river flow during monsoon time is 29☗% in the head water segment of Cauvery River, denoting region upstream of KRS reservoir, whereas in the downstream segment the average groundwater contribution increases to 55☗%. The average groundwater contribution to river flow during pre-monsoon season is 75±5% in the head water segment of Cauvery River, whereas in the downstream segment of the KRS reservoir the average groundwater contribution drops to 49☓%. We used two-component mixing model to estimate the average contribution of base flow to the Cauvery River during the pre-monsoon and south-west monsoon seasons. pre-monsoon season registered increase in the river water isotope values. The Krishna Raja Sagar (KRS) Reservoir controls the river water isotopic composition by evaporative process, which varies seasonally i.e. Isotopically heavier values are recorded for the pre-monsoon season coinciding with the period of low flow condition, whereas the monsoon season is characterized by high discharge and recorded isotopically lighter values.
Isotopic composition of river water within the Cauvery Basin showed distinct shift at seasonal time interval. Stable isotope measurements showed a seasonal shift in the river water isotopic values (δ2H 8‰, δ18O 0.95‰) between pre- monsoon (PM) and south-west monsoon (SWM) seasons. Field campaigns yielded seasonal datasets for the Cauvery river water and groundwater isotopic composition. Samples are collected during seasonal time interval spanning from 2014 - 2016, covering pre-monsoon (PM), south-west monsoon (SWM) and north-east monsoon (NEM) seasons. Stable Isotope measurements (δ2H, δ18O) of Cauvery river water along with groundwater are carried out using consistent sampling protocols. The study investigates the seasonal contribution of surface runoff and baseflow to the Cauvery streamflow using isotope mass balance approach. This study confirmed that the selected climate model not only leads to the different predictions in the groundwater depletion, yet also results in a different degree of confidence in the model simulations. Yet, a significant reduction in the hydraulic head (approximately 114 m) and storage change (-17.25 %) – particularly in the western part of the aquifer – is expected in 2100, according to RCP8.5. The study revealed that there is not necessarily a substantial difference tracked over the estimated groundwater levels between the RCP4.5 and RCP8.5 scenarios until the end of 2050s. To assess the changes in groundwater level and storage, we applied our experimental design in the Şuhut alluvial aquifer in Akarçay Basin (Turkey). To estimate the model forcing input (recharge and evapotranspiration) for the hydrogeological model, we used precipitation and temperature outputs from two Global Circulation Models, namely HadGEM2-ES and MPI-ESM-MR.
To achieve so, we simulated the groundwater flow using the HİDROTÜRK hydrogeological model under the climate change projections considering the RCP4.5 and RCP8.5 scenarios. In this study, we examined the potential impact of climate change on the depletion of groundwater levels and storage.
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