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In addition to surface water, groundwater is an essential source of water for agriculture, industry, and living in Ha Tinh province (central Vietnam). However, overexploitation and unreasonable use of groundwater has put this resource at risk of endangerment and pollution. In the coastal areas especially, the impact of climate change and the rise in sea-level has increased the risk of salt-water intrusion into groundwater. In this study, the groundwater system model (GSM) is applied to simulate the intrusion of saline water in different climate change scenarios in the coastal area of Ha Tinh province. The result reveals that saline intrusion into groundwater is becoming more complex and is a rising trend in climate change scenarios RCP4.5 and RCP8.5.
Environmental Sciences | Climatology Doi: 10.31276/VJSTE.60(4).82-88 Projection of saline intrusion into groundwater in the context of climate change in the coastal zone of Ha Tinh province Van Dai Nguyen*, Tien Anh Do, Kim Tuyen Nguyen Vietnam Institute of Meteorology, Hydrology and Climate Change Received 30 June 2018; accepted 19 September 2018 Abstract: Introduction In addition to surface water, groundwater is an essential source of water for agriculture, industry, and living in Ha Tinh province (central Vietnam) However, overexploitation and unreasonable use of groundwater has put this resource at risk of endangerment and pollution In the coastal areas especially, the impact of climate change and the rise in sea-level has increased the risk of salt-water intrusion into groundwater In this study, the groundwater system model (GSM) is applied to simulate the intrusion of saline water in different climate change scenarios in the coastal area of Ha Tinh province The result reveals that saline intrusion into groundwater is becoming more complex and is a rising trend in climate change scenarios RCP4.5 and RCP8.5 Salt-water intrusion into surface water and groundwater is a frequent problem in the coastal areas of Ha Tinh province, as well as in other provinces and cities With the current socio-economic growth rate, water demand from various sectors is increasing dramatically; on the other hand, with the impact of climate change, surface water as a resource is diminishing and pollution levels are rising This, in turn, depletes the available store of surface water that sectors depend on In this context, groundwater would be an effective solution to provide for the needs of socioeconomic development, especially where exploitation of surface water is no longer possible However, as with surface water, groundwater also faces the risk of seawater intrusion; hence, if there are no solutions to reducing saltwater infiltration, or rationally using and supplementing fresh water for groundwater, coastal resources will diminish and fail to supply the needs of socio-economic development In this study, the GSM is applied to simulate groundwater level and assess saline intrusion in climate change scenarios over extended periods of time in the coastal areas of Ha Tinh (including seven coastal districts, two towns, and one city: Nghi Xuan, Duc Tho, Can Loc, Loc Ha, Thach Ha, Cam Xuyen, and Ky Anh districts; the city of Ha Tinh; and the towns of Ky Anh, Hong Linh) The primary objective of this study is to assess the impact of climate change on coastal groundwater resources Keywords: climate change, coastal, groundwater, Ha Tinh, saline intrusion Classification number: 5.2 Method and data Method The GSM model was applied to simulate the groundwater resource for the coastal area of Ha Tinh province: The GSM is a model that integrates the MODFLOW [1] groundwater flow model and the MT3DMS [2] waterquality model to simulate groundwater flow and quality In the MODFLOW model, the three-dimensional *Corresponding author: Email: nguyendai.tv@gmail.com 82 Vietnam Journal of Science, Technology and Engineering December 2018 • Vol.60 Number study is to assess the impact of climate change on coastal groundwater The partial differential describing the fate and transporting of and transporting of Theequation partial differential equation describing the fate resources contaminants of species k in 3D, of transient flow systems can beflow systems can be contaminants speciesgroundwater k in 3D, transient groundwater written as follows: written as follows: Method and data Method (C k ) (Ck()C k ) k (Ck k ) D) ij qs Cs Rn (vi C k ) qs Csk(2) Dij (v C The GSM model was applied to simulate the groundwater resource for the t x x i the | Climatology transporting The partial differential fate and of Rn Environmental Sciences t xi equation x j describing x i i j xi coastal area of Ha Tinh province (2) contaminants of species k in 3D, transient groundwater flow systems can be The GSM is a model that integrates the MODFLOWwritten [1]Where: groundwater Where: as follows: flow model and the MT3DMS [2] water-quality model to simulate groundwater of sub-surfaceof medium, consideredmedium, to be considered to be : the porosity the the sub-surface : (the (C k ) the relationship C k ) porosity flow and movement quality k of a groundwater level of a constant density dimensionless Dij vi =(qvii C/θ ) qs Csk Rn (2) dimensionless xi xi -3 k x j -3 In through the MODFLOW the three-dimensional movement ofdissolved a t porous model, earth material may be described the species concentration of k, ML Ck:by : dissolved concentration of species k, ML C of the qs: volumetric flow rate per unit of the volume groundwater level of partial a constant density through porous earth materialt:maytime, be T following differential equation: t: representing time, T Where: aquifer, fluid sources (positive) and sinks described by the following partial differential equation: coordinate axis, L coordinate axis, L xi,j: distance along the : distance along the relevant Cartesian xi,jrelevant -1 Cartesian coefficient porosity(negative), ofdispersion the Tsub-surface medium, to be considered -1 h h h h : Dijthe : hydrodynamic tensor, L T D : hydrodynamic dispersion coefficient tensor, L2T-1 ij K xx K yy K zz W Sdimensionless (1)(1) -1 s k seepage or linear waterorvelocity, LT ;water this is related to-1;the x x y y z z t : pore seepage linear velocity, this is related to the k v i: -3 pore Cs v: iconcentration of the source or sink flux LT for species : dissolved concentration of species k, ML C qthe specific discharge or specific Darcy flux by means of the relationship vi = discharge or Darcy flux by means of v i = qi / i / relationship Where: -3 where: t: time, T k, ML qs: volumetric flowqs.: rate per unitflow of the volumetric rate volume per unitof ofthetheaquifer, volume of the aquifer, xx, along the relevant Cartesian coordinate axis,-1L - Kxx, Kyy, Kzz: are values of hydraulic conductivity along the and zfluid i,j: y,distance -1 representing (positive) andsources sinks (negative), T sinks representing fluid (positive) -3 -1 (negative), T , Kassumed : are values of hydraulic conductivity along sources - Kxx, Kyyare -1 and zz Rk n: chemical coefficientreaction tensor, Lterm, T ML T -3 coordinate axes, which to be parallel to the major axes D ofij:hydraulic khydrodynamic dispersion -3 C : concentration of the or sink flux forsource species k, MLflux Cs :source of the for species k, ML the(L/T) x, y, and z coordinate axes, which are assumed to be or linear conductivity vi: sseepage poreconcentration water -3velocity, LT-1; thisor-3issink related to the -1 -1 reaction ML of T reaction Rn : chemical term, ML Rterm, parallel to the major axes of hydraulic conductivity (L/T) left-hand n : chemical specific discharge or Darcy flux by means the v2i =T qi / be expanded into - h: is the potentiometric head (L) The side ofrelationship Equation can ∑ volumetric flowofterms: rate left-hand per unit the volume ofbe the aquifer, s:The left-hand side Equation canside beofof expanded into two terms: The Equation can expanded into two terms: two h: is the flux potentiometric head (L) sources qand/or - W: is a -volumetric per unit volume representing sinks representing andk sinks (negative), T-1 of water, with W < 0.0 for flow out of the groundwater system, and Wk > 0.0fluid for sources (positive) k k k k k -3 ( C ) C C (C ) qC'k,CML for C k k - W: is Cs : concentration of the source or sink Cflux species flow into the system (T-1a).volumetric flux per unit volume representing C k q(3) ' s C k (3) (3) t -3t -1 t t t st t t -1 forR flow sources and/or sinks of water, with W < 0.0 out chemical reaction term, ML T : - S: is the specific storage capacity of the porous material (L ) n of the groundwater system, and W > 0.0 for flow into the -1 - t: is time (T) -1 q's side is the rate of change transient storage (unit, ) storage (unit, T-1) Where: q's 2 canin isbe the rate change transient groundwater The left-hand ofWhere: Equation expanded into two is the ofgroundwater rate ofin terms: change in Ttransient where: t system (T ) t This equation describes water-level dynamics in heterogeneous and (C k ) C k C k -1 Ck (3) groundwater storage (unit, T ).q's C k anisotropic environments - S: is the specific storage capacity of the porous The material chemical reaction term in equation can be used to include thebeeffect t t t t The chemical reaction term in equation can used to include the effect -1 ) MT3DMS water quality model, transporting of (L the With solutions a generalin biochemical and chemical geochemical reactions onintheequation fate reactions and2transport of fate and transport of of general biochemical and geochemical on the The reaction term can be -1 used to porous environment is a complex chemical and physical process Two q's basicisConsidering Where: the rate of change in transient groundwater storage (unit, T ) contaminants only two basic types of chemical reactions, that is, contaminants Considering only two basic types of chemical reactions, that is, - t:theis process time (T) include the effect of general biochemical and geochemical t components of are (i) the transporting of hydrodynamics and (ii) aqueous-solid surfaceaqueous-solid reactions (sorption) and first-order rate and reactions, the rate reactions, the surface reactions (sorption) first-order diffusion of ions and particles are dissolved in water from the high concentration reactions on the asfate and transport of contaminants reaction can be expressed follows: This equation describes water-level chemical dynamics in term chemical reaction term can be expressed as follows: to the low concentration When contaminated water flows through The the porous chemical reaction term in only equation 2basic can be usedof to chemical include thereactions, effect Considering two types that k heterogeneous and anisotropic k environment, it mixes with uninfected water by environments means of mechanical dispersion Csurface C of general biochemicalis,and geochemical reactions and transport of k on the k fate k and first-order k aqueous-solid reactions (sorption) 1C R n2 bC b 1C 2 bC (4) (4) Rn b t types that dilutes it and reduces its concentration Molecular diffusion and mechanical contaminants Considering only two basic of chemical is, tterm canthat Withbe the MT3DMS water quality model, transporting rate reactions, the chemical reaction reactions, be expressed dispersion cannot separated in an underground stream and both processes are aqueous-solid surface reactions (sorption) and first-order rate reactions, the in a porous environment is a complex chemical referred tosolutions as hydrodynamic dispersion asWhere: follows: Where: chemical and physical process Two basic components of thereaction processterm can be expressed as follows: -1 medium, ML ρb: bulk density of theρbsub-surface : bulk density of the sub-surface medium, ML-1 C k -1 are (i) the transporting of2 hydrodynamics and (ii) Cdiffusion k k k k : concentration ofRC species subsurface solids, MM b k sorbed 1Conof the species k sorbed on the subsurface solids, (4) (4) MM-1 n :concentration bC -1 t of ions and particles are dissolved in water from the high -1 for the dissolved phase, : first-order reaction rate for Tthe dissolved phase, T 1 rate : first-order reaction concentration to the low concentration When contaminated for the sorbed (solid) phase, T-1 2 : first-order reaction Where: : first-order reaction rate for the sorbed (solid) phase, T-1 2 rate water flows through the porous environment, it mixes with where: ρb: bulk density of the sub-surface medium, ML-1 uninfected water by means of mechanical dispersion that of the sub-surface medium, ML-1 ρb: bulkkdensity sorbed on the subsurface solids, MM-1 C k : concentration of species dilutes it and reduces its concentration Molecular: diffusion : concentration of species Ckrate for the dissolved phase, T-1k sorbed on the subsurface 1 first-order reaction and mechanical dispersion cannot be separated in an solids, MM-1 -13 2 : first-order reaction rate for the sorbed (solid) phase, T underground stream and both processes are referred to as λ1: first-order reaction rate for the dissolved phase, T-1 hydrodynamic dispersion λ2: first-order reaction rate for the sorbed (solid) phase, The partial differential equation describing the fate and The partial differential equation describing the fate and transporting of T-1 transporting of speciesflow k insystems 3D, transient contaminants of species of k incontaminants 3D, transient groundwater can be Substituting equations and into equation and flow systems can be written as follows: written asgroundwater follows: omitting theequations species in order simplify the Substituting andindex into equation andtoomitting the species (C k ) (C k ) D (v C k ) qs Csk Rn (2)(2) index presentation, Equation can be rearranged andberewritten in order to simplify the presentation, Equation can rearranged as: and t xi ij x j xi i Where: rewritten as: where: : the porosity of the sub-surface medium, considered to be dimensionless.θ: the porosity of the sub-surface medium, considered to Ck: be dissolved concentration of species k, ML-3 dimensionless t: time, kT concentration of species k,L.ML-3 C : dissolved xi,j: distance along the relevant Cartesian coordinate axis, -1 Dij: hydrodynamic t: time, T.dispersion coefficient tensor, L T vi: seepage or linear pore water velocity, LT-1; this is related to the along the relevant Cartesian axis, xi,j: distance = qi / specific discharge or Darcy flux by means of the relationship vi coordinate L qs: volumetric flow rate per unit of the volume of the aquifer, representing fluid (positive) and sinks (negative), T-1 tensor, L2T-1 hydrodynamic dispersion coefficient Dij: sources -3 k Cs : concentration of the source or sink flux for species k, ML -3 -1 linear water velocity, LT-1; this is vi: seepage reaction or term, ML Tpore Rn : chemical related to the specific discharge or Darcy flux by means of The left-hand side of Equation can be expanded into two terms: (C k ) C k C k Ck q' s C k t t t t Where: q's (3) C C C b Dij (viC ) qsCs q's C 1C 2 bC t t xi x j xi Equation is 5a mass is, the change Equation is abalance mass statement, balancethat statement, thatin the is, mass the storage (both dissolved and sorbed phases) at any given time is equal to the change in the mass storage (both dissolved and sorbed difference between the mass inflow and outflow due to dispersion, advection, phases)and at any given time is equal to the difference between sink/source, chemical reactions theLocal mass inflow isand duethetovarious dispersion, advection, equilibrium oftenoutflow assumed for sorption processes (i.e., sink/source, andfast chemical sorption is sufficiently relative toreactions the transport time scale) When the local equilibrium assumption is invoked, it is customary to express equation in the Local following form: equilibrium is often assumed for the various sorption processes (i.e., sorption is sufficiently fast relative C C scale) When the local equilibrium to the R transport Dij time (viC ) qsCs q's C 1C 2 bC (6) t xi x j xi Where: R is referred to as the retardation factor, which is a dimensionless factor defined as: is the rate of change in transient groundwater storage (unit, T-1) b C Vietnam Journal of Science, t R 1 December 2018 • Vol.60 Number C Technology and Engineering The chemical reaction term in equation can be used to include the effect of general biochemical and geochemical reactions on the fate and transport of (5) (5) 83(7) When the local equilibrium assumption is not appropriate, sorption processes are typically represented through a first-order kinetic mass transfer rewritten as: C C C b Dij (viC ) qsCs q's C 1C 2 bC t t xi x j xi (5) Equation is a mass balance statement, that is, the change in the mass storage (both dissolved and sorbed phases) at any given time is equal to the Environmental Sciences | Climatology difference between the mass inflow and outflow due to dispersion, advection, sink/source, and chemical reactions Local equilibrium is often assumed for the various sorption processes (i.e., sorption is sufficiently fast relative to customary the transport time scale) When the local assumption is invoked, it is to express equation equilibrium assumption is invoked, it is customary to express equation in the in the following form: following form: R C C D (v C ) qsCs q's C 1C 2 bC t xi ij x j xi i (6) (6) Where: R is referred to as the retardation factor, which is a dimensionless factor where: defined as: R is referred to as the retardation factor, which is a dimensionless factor defined as: C R 1 b C (7) ρb ∂ C R = 1the + local (7) When q ∂ Cequilibrium assumption is not appropriate, sorption processes are typically represented through a first-order kinetic mass transfer equation, as discussed in the section on chemical reactions when the local equilibrium assumption is not appropriate, Data sorption processes are typically represented through a firstInputkinetic data for the GSMtransfer include: equation, as discussed in the order mass - Hydrometeorological data: meteorological and hydrographic data up to section on chemical reactions 2014 from the project “Technical consultancy on the hydrological/hydraulic Data model of the Rao Cai river basin and the drainage model in the city of Ha Tinh, Ha Tinh province” were also part of the project “Integrated water resource Input data for the GSM include: management and urban development in Ha Tinh province”, conducted by the Vietnam- Academy for Water Resources [3] Additional data up to 2016 and were Hydrometeorological data: meteorological collected from the Hydrometeorological Centre the National Center of hydrographic data up to 2014Data from theofproject “Technical Meteorology and on Hydrology (now the Meteorological and of Hydrological consultancy the hydrological/hydraulic model the Rao Administration) Cai river basin and the drainage model in the city of Ha Tinh, Land-use data: land-use status part data of forthe Ha project Tinh from 2015 were Ha- Tinh province” were also “Integrated collected from Center for Land Assessment under Center for Land Survey and water resource management and urban development in Planning under General Department of Land Administration Ha Tinh province”, conducted by the Vietnam Academy for Water Resources [3] Additional data up to 2016 were collected from the Hydrometeorological Data Centre of the National Center of Meteorology and Hydrology (now the Meteorological and Hydrological Administration) - Land-use data: land-use status data for Ha Tinh from 2015 were collected from Center for Land Assessment under Center for Land Survey and Planning under General Department of Land Administration - Stratigraphic data: the 2014 1:200,000-scale hydrogeological map of Ha Tinh province was sourced from the National Center for Water Resource Planning and Investigation - The stratigraphic data on hydro-geological boreholes were inherited from the project “Planning, exploitation, utilization, and protection of water resources in Ha Tinh province up to 2020”, conducted by the 2F Division for Water Resources Planning and Investigation of the Ministry of Natural Resources and Environment in 2011 [4] - Survey data: survey data were collected by means of interviews with local people using pre-designed table templates, and by means of direct water sampling The scope and subjects of the survey were the current status of water use in 330 households and 20 organisations in 10 coastal districts/cities/towns of Ha Tinh province - Climate-change scenarios: climate-change in Ha Tinh 84 Vietnam Journal of Science, Technology and Engineering province was examined in terms of two scenarios, RCP4.5 and RCP8.5, for temperature (Table 1), precipitation (Table 2) and sea level rise (Table 3) extraction from climate change and sea-level rise scenarios for Vietnam, which were updated by Ministry of Natural Resources and Environment in 2016 [5] Table Changes in temperature (oC) compared to the period 1986-2005 in terms of different climate change scenarios in Ha Tinh province RCP4.5 RCP8.5 Temperature 2016-2035 2046-2065 2080-2099 2016-2035 2046-2065 2080-2099 Annual 0.6 (0.3÷1.0) 1.5 (1.0÷2.1) 2.0 (1.4÷2.9) 0.9 (0.6÷1.3) 1.9 (1.3÷2.8) 3.5 (2.8÷4.8) Winter 0.6 (0.3÷1.0) 1.3 (0.7÷1.8) 1.6 (1.0÷2.1) 0.9 (0.6÷1.2) 1.7 (1.2÷2.4) 2.8 (2.0÷3.7) Spring 0.6 (0.1÷1.2) 1.3 (0.7÷1.9) 2.0 (1.2÷2.9) 0.9 (0.5÷1.3) 1.8 (0.9÷2.8) 3.2 (2.0÷4.5) Summer 0.8 (0.4÷1.3) 1.9 (1.2÷3.0) 2.6 (1.8÷3.6) 1.0 (0.5÷1.5) 2.3 (1.4÷3.6) 4.1 (3.2÷5.7) Autumn 0.6 (0.3÷1.1) 1.5 (1.0÷2.2) 2.0 (1.2÷2.9) 0.8 (0.4÷1.4) 2.0 (1.3÷3.0) 3.6 (2.7÷5.0) Source: Vietnam Institute of Meteorology, Hydrology and Climate Change (IMHEN) Table Changes in rainfall (%) relative to the period 1986-2005 in terms of climate change scenarios in Ha Tinh province RCP4.5 Rainfall RCP8.5 2016-2035 2046-2065 2080-2099 2016-2035 2046-2065 2080-2099 Annual 11.3 (6.0÷16.6) 16.3 (8.5÷24.4) 13.0 (3.4÷22.6) 12.9 (6.8÷18.9) 14.1 (8.9÷19.0) 17.4 (10.6÷24.4) Winter 12.0 (4.1÷19.5) 21.0 12.8 (11.4÷30.4) (5.4÷20.0) 3.5 (-2.1÷9.2) 13.0 (1.6÷24.4) 19.8 (6.5÷33.2) Spring 2.8 (-3.7÷9.2) 14.5 (4.3÷23.9) 9.4 -4.2 5.0 (-1.8÷20.5) (-14.4÷5.8) (-3.5÷13.0) 16.1 (2.1÷30.5) Summer 21.1 9.1 4.8 40.6 (-3.7÷44.7) (-2.1÷20.3) (-5.7÷16.1) (5.0÷70.7) Autumn 9.9 (3.8÷16.1) 19.0 (5.2÷31.6) 17.6 (3.8÷30.3) 18.6 (-6.5÷43.4) 8.2 15.1 (-0.1÷15.8) (6.6÷23.4) 22.2 (3.0÷41.8) 17.6 (8.2÷27.0) Source: IMHEN Table Sea-level rise scenarios for the coastal areas of Ha Tinh province (cm) Scenarios Timeline of the 21st century 2030 2040 2050 2060 2070 2080 2090 2100 RCP4.5 13 17 (8÷18) (10÷24) 22 (13÷31) 27 (16÷39) 33 39 (20÷47) (24÷56) 46 53 (28÷65) (32÷75) RCP8.5 13 18 (9÷18) (12÷26) 25 (17÷35) 32 (22÷45) 40 50 (28÷57) (34÷71) 60 72 (41ữ85) (49ữ102) Source: IMHEN December 2018 Vol.60 Number Environmental Sciences | Climatology - Boundary conditions: + The sea boundary is approximately 143 km, from the Lam river mouth to the end of Ky Anh town, next to Quang Binh province + The river boundary comprises four major rivers, the Lam, Ha, Lui, Quyen, and their major branches (Fig 2) + The groundwater restoration boundary was Fig Computational domain and computational the Fig the Sea and river boundaries in the research area calculatedgrid by ofsubtracting research area evaporation boundary from the Fig Sea and river boundaries in the precipitation boundary in the research area corresponding exposure area of Holocene layer Results and discussion geological layers in the research Pleistocene layer The GSM model constructed for the coastal area of Ha area (Fig and Table 4) Neogen, Triat, OrdovicTinh province Silur layer - The computational domain includes the coastal districts of Nghi Xuan, Duc Tho, Can Loc, Loc Ha, Thach Ha, Cam Xuyen, and Ky Anh; the city of Ha Tinh; and the towns of Ky Anh, Hong Linh (Fig 1) - The computational grid includes 563,060 grid points, including 294,865 computational points Grid cell size is 200 m x 200 m Fig Exposure of geological in the research area Fig area Exposure arealayers of geological layers in - Boundary conditions: the research area + The sea boundary is approximately 143 km, from the - A 3-year period was used to warm up the model to Lam river mouth to the end of Ky Anh town, next4.toClassification Quang Table of the restoration area in the coastal reduce thegroundwater effect of initial conditions Binh province area of Ha Tinh province - Computational time step: daily + The river boundary comprises four major rivers, the Restoration rate No 2) Restoration area Calibration and validation Lam, Ha, Lui, Quyen, and their major branches (Fig from rainfall (%) + The groundwater restoration boundary was1calculated HoloceneFor model calibration, this 35 research employs monitoring by subtracting the evaporation boundary from the data from January 2014 to December 2016 from four Pleistocene 35 precipitation boundary in the corresponding exposure area groundwater level stations within research area (Table 5) Table 4) Neogen, Triat, Ordovic-Silur 15 of geological layers in the research area (Fig and Table Classification of the groundwater restoration area in the coastal area of Ha Tinh province Table Differences between the simulated water level and the water level measured at groundwater level monitoring wells in the research area.7 No Station Mean absolute difference Root mean square deviation Maximum difference (m) No Restoration area Restoration rate from rainfall (%) QT2a-HT_0 0.05 0.004 0.15 Holocene 35 QT5a-HT_0 0.13 0.023 0.32 Pleistocene 35 QT6-HT_0 0.18 0.057 0.91 Neogen, Triat, Ordovic-Silur 15 QT6b-HT_0 0.13 0.039 0.81 December 2018 • Vol.60 Number Vietnam Journal of Science, Technology and Engineering 85 January 2014 to December 2016from four groundwater level stations within research area (Table 5) Table Difference s between the simulated water level and the water level measured at groundwater level monitoring wells in the research area MeanSciences absolute Root mean Maximum | Climatology Environmental No Station difference square deviation difference (m) QT2a-HT_0 0.05 0.004 0.15 QT5a-HT_0 0.023 0.32 The results of0.13 the model calibration and validation show that the model parameters are 0.057 reliable and can0.91 be applied QT6 -HT_0 0.18 to research on groundwater in the coastal area of QT6b-HT_0 0.13 0.039 0.81Ha Tinh change of rainfall and a sea level rise of 0.09 m By 2030, in terms of scenarios RCP4.5 and RCP8.5, the storage tends to decrease relative to the current situation In that year, the level of salinity intrusion tends to decrease in all the months Salt-water reserve terms and of validation the climate change The results of the model in calibration show that the model of the year in terms of both RCP4.5 and RCP8.5 scenarios, scenarios parameters are reliableand can be applied to research on groundwater in the with the largest decrease occurring in August This change coastal area of Ha Tinh The results of calculating the salt-water storage in the is primarily due to a change in rainfall by 2030, which is Salt-water reserve in terms oflayers the climate change scenarios Holocene and Pleistocene in 2020 and 2030 in terms quite similar for both RCP4.5 and RCP8.5 scenarios and the The results RCP4.5 of calculating salt-water storage in tothethe Holocene of scenarios and the RCP8.5 compared currentand scenario of a 0.13 m rise in sea level Pleistocene and 2030 of scenarios RCP4.5 andinRCP8.5 situationlayers (thein 2020 average of in theterms period 1986-2005) the compared to the current sit uation (the average of the period 1986-2005) in the The magnitude of saline intrusion in 2020 and 2030 coastal area of Ha Tinh province are shown in Figs 4A , 4B coastal area of Ha Tinh province are shown in Fig 4A and Fig 4B is less than that of the (current) baseline period due to a 704 Current status (1986-2005) RCP4.5 (2020) RCP8.5 (2020) significant increase in rainfall in these years 702 Volumn (10 m3) 700 698 696 694 692 690 688 686 684 I II III IV V VI (A) VII VIII IX X XI XII The results of calculating salt-water storage in the Holocene and Pleistocene layers for the periods 2016-2035, 2046-2065, and 2080-2099 in terms of the RCP4.5 and RCP8.5 scenarios compared to the current situation in the thencoastal it increases at theprovince end of theare century (2080 With 5B scenario areagradually of Ha Tinh shown in-2099) Figs 5A, RCP8.5, in the early years of the 21st century (2016-2035) groundwatersalinity shows trends of salinity intrusion into intrusionFigure increase5s in July, the August, September , November, and December compared to the current s inarethe remaining months groundwater in the situation, researchand area,decrease which very complex st However, in the last years of the 21 century (2080-2099), saline st intrusion into With scenario RCP4.5, in the early years of the 21 century groundwatertends to increase sharply in comparison with that ofall months of (2016-2035) the level of salinity intrusion tends to decrease; the year 704 Current status (1986-2005) 702 RCP8.5 (2030) Period 2046-2065 706 Period 2080-2099 704 Volumn (10 m3) 700 Volumn (10 m3) RCP4.5 (2030) 698 696 694 692 702 700 698 696 694 692 690 690 688 I II III IV V VI VII VIII IX X XI XII I II III IV V VI VII VIII IX X XI XII (A) (B) Fig Salt-water storage diagrams in the Holocene and Fig Salt -water storage the Holocene layers Pleistocene layers in diagrams 2020 (A)inand 2030 (B)and in Pleistocene the research inarea 2020according (A) and 2030 ( B ) in the research according to scenarios to scenarios RCP4.5 andarea RCP8.5 RCP4.5 and RCP8.5 706 Current status (1986-2005) Period 2016-2035 Period 2046-2065 Period 2080-2099 Volumn (10 m3) 704 The in Fig show4 that groundwater salinity in thesalinity research area Theresults results in 4Fig show that groundwater in in 702 2020 in terms of scenarios RCP4.5 and RCP8.5 tends to decrease compared with 700 the research area in 2020 in terms of scenarios RCP4.5 the current situation By 2020, the level of salinity intrusion tends to decrease in 698 RCP8.5 decrease compared with the current alland months of thetends year in to both the RCP4.5 and RCP8.5 scenarios For both situation By 2020, theoccurs levelinofJuly, salinity to for 696 scenarios, the largest decrease and theintrusion smallest intends January decrease all months the year in both the occurs RCP4.5 RCP4.5 , and in in December for of RCP8.5 This phenomenon dueand to the 694 hypothesis the problem claims thatscenarios, the amountthe of largest groundwater extraction 692 RCP8.5 ofscenarios For both decrease remains unchanged to smallest the currentinsituation ; thisfor change may primarily I II III IV V VI VII VIII IX X XI XII occurs in July,relative and the January RCP4.5, and (B) bein dueDecember to the change of rainfall and a sea level rise of 0.09 m By 203 0, in terms for RCP8.5 This phenomenon occurs due to of scenarios RCP4.5 and RCP8.5 , the storage tends to decreaserelative to the Fig Saltwater storage charts in the Holocene and Pleistocene the hypothesis of the problem claims that the amount ofFig Saltwater storage charts in the Holocene and Pleistocene layers of current situation In that year, the level of salinity intrusion tends to decrease in layers of the research area for the periods 2016-2035, 2046extraction remains unchanged relative to thewith 2065, and in terms of scenarios RCP4.5 (A) and in area2080-2099 for the periods 2016 -2035, 2046-2065, and 2080-2099 the research allgroundwater the months of the yearin terms of both RCP4.5 and RCP8.5 scenarios, (B) RCP4.5 (A) and RCP8.5 ( B ) situation; this change may due todue thetoterms of scenarios thecurrent largest decrease occurring in August Thisprimarily change is be primarily a RCP8.5 change in rainfall by 2030, which is quite similar for both RCP4.5 and RCP8.5 Area of salinity intrusion in terms of the climate change scenarios scenarios andthe scenario of a0.13 m rise in sea level As shown in Fig 6, by 2020 and 2030, salinity will intrude into both the The magnitude of saline intrusion in 2020 and 2030 isless than that of the Holocene and Pleistocene layers in terms of both climate change scenarios, Vietnam Journal of Science, 2018 Vol.60 86 baseline period due to asignificant increase (current) in rainfall in •these years.Number RCP4.5 and4 RCP8 5; however, in the 1986-2005 baseline period, intrusiononly Technology and Engineering December occurred near the river banks and rivermoutharea The results of calculating salt-water storage in the Holocene and Pleistocene layers for the periods 2016-2035, 2046-2065, and 2080-2099 in Environmental Sciences | Climatology Holocene layer in terms of the RCP8.5 scenario Holocene layer in terms of the RCP4.5 scenario 10.5 10 Area (1,000 ha) Area (1,000 ha) 11 9.5 8.5 Pleistocene layer in terms of the RCP4.5 scenario Pleistocene layer in terms of the RCP8.5 scenario 12.5 Area (1,000 ha) Area (1,000 ha) 13 10.4 10.2 10 9.8 9.6 9.4 9.2 8.8 8.6 12 11.5 11 12.8 12.6 12.4 12.2 12 11.8 11.6 11.4 11.2 11 Fig Surface area of groundwater salinisation in terms of the climate change scenarios in the coastal area of Ha Tinh province then it increases gradually at the end of the century (20802099) With scenario RCP8.5, in the early years of the 21st century (2016-2035) groundwater salinity intrusion increases in July, August, September, November, and December compared to the current situation, and decreases in the remaining months However, in the last years of the 21st century (2080-2099), saline intrusion into groundwater tends to increase sharply in comparison with that of all months of the year and Pleistocene layers are similar in each climate change scenario In terms of the RCP4.5 scenario, the area of saline groundwater is lower than the current one in the early and mid-21st century and is higher at the end of the century In terms of the RCP8.5 scenario, the area of saline groundwater does not change substantially relative to the status in the early and mid-21st century, and increases at the end of the century As shown in Fig 7, the area of salt-water intrusion in the Holocene layer is primarily in Ky Anh town and Nghi Xuan, Thach Ha, and Cam Xuyen districts, with area itself ranging from 1,500 to over 2,000 ha; while in the coastal districts, the area of saline intrusion into the groundwater ranges from 300 to over 600 In the Pleistocene layer, the largest areas of saltwater intrusion are in Ky Anh district and Ky Anh town with over 2,000 Nghi Xuan and Cam Xuyen districts experience 1,900 of intrusion and Thach Ha district approximately 1,500 In the remaining districts, the area of saltwater intrusion is approximately equal to that which occurs in the Holocene layer This trend of changes in the area of saline intrusion into groundwater is similar to that in the other areas in coastal Ha Tinh Area of salinity intrusion in terms of the climate change scenarios As shown in Fig 6, by 2020 and 2030, salinity will intrude into both the Holocene and Pleistocene layers in terms of both climate change scenarios, RCP4.5 and RCP8.5; however, in the 1986-2005 baseline period, intrusion only occurred near the river banks and rivermouth area The results in Fig show that, in terms of all climate change scenarios considered, the area of saline groundwater in both the Pleistocene and Holocene layers slightly varies from month to month during the year The changing trends in the area of saline groundwater intrusion in the Holocene December 2018 • Vol.60 Number Vietnam Journal of Science, Technology and Engineering 87 Environmental Sciences | Climatology 2,500 decrease slightly, and thereafter it increases gradually at the end of the century Holocene layer in terms of the RCP4.5 scenario 1986-2005 2020 2030 2016-2035 2046-2065 2080-2099 Area (ha) 2,000 1,500 1,000 500 Nghi Hong Linh Duc Tho Can Loc Xuan town 2,500 Loc Ha Thach Ha Ha Tinh city Cam Xuyen Ky Anh dist Ky Anh town Holocene layer in terms of the RCP8.5 scenario 1986-2005 2020 2030 2016-2035 2046-2065 2080-2099 Area (ha) 2,000 1,500 1,000 500 2,500 Nghi Hong Linh Duc Tho Can Loc Xuan town Loc Ha Thach Ha Ha Tinh city Cam Xuyen Ky Anh dist Ky Anh town Pleistocene layer in terms of the RCP4.5 scenario 1986-2005 2020 2030 2016-2035 2046-2065 2080-2099 Area (ha) 2,000 1,000 500 2,500 Nghi Hong Linh Duc Tho Can Loc town Xuan Loc Ha Thach Ha Ha Tinh city Cam Xuyen Ky Anh dist Ky Anh town 2020 2030 2016-2035 2046-2065 Area (ha) The research was supported by the project "Consultant to study the impact of climate change on underground water resources in Ha Tinh province and propose a sustainable management solution" The authors declare that there is no conflict of interest regarding the publication of this article Pleistocene layer in terms of the RCP8.5 scenario 1986-2005 2080-2099 2,000 REFERENCES 1,500 [1] 2F Division for Water Resources Planning and Investigation (2011), Project “Planning, Exploiting, Utilizing and Protecting Water Resources in Ha Tinh Province up to 2020” 1,000 500 These results are calculated based on the averages for periods of heavy and light rainfall, so the trend of an increase in levels of salinity in groundwater is not clear In fact, salt-water intrusion frequently occurs during the years of light rainfall, especially in the months of the dry season It is therefore necessary to undertake a more detailed examination for each year, especially those of lighter rainfall in order to obtain a more specific assessment of the impact of climate change on groundwater The results of this study provide the premise and basis for further research ACKNOWLEDGEMENTs 1,500 According to the climate change scenarios, at the beginning of the century, rainfall in Ha Tinh increased and so did the reserve of underground water in the province; at the end of the century, the sea level in Ha Tinh will rise (by 68 cm), saline intrusion into groundwater will increase, and groundwater saline storage will tend to decrease slightly relative to the beginning of the century Nghi Hong Linh Duc Tho Can Loc Xuan town Loc Ha Thach Ha Ha Tinh city Cam Xuyen Ky Anh dist Ky Anh town Fig.7.7.Surface Surface area groundwater salinisation in terms the 12 salinisation Fig a rea of of groundwater in terms of the of climate climate change scenarios in theof coastal districts of Ha Tinh change scenarios in the coastal districts Ha Tinh province province As shown in Fig 7, the area of salt-water intrusion in the Holocenelayer is primarily in Ky Anh town and Nghi Xuan, Thach Ha, and Cam Xuyen Conclusions districts, with area itself ranging from 1,500 to over 2,000 ha; while in the coastal districts, the area of saline intrusion into thegroundwater ranges from Saline intrusion tends to decrease in areas terms the 300 to overwater 600 In the Pleistocene layer, the largest of of saltwater and Ky Anh town with over 2,000 ha.and Nghi intrusion are in Kychange Anh district two climate scenarios considered - RCP4.5 Xuan and Cam experience 1,900 hastorage of intrusion Thach Ha RCP8.5 - byXuyen 2020districts and 2030: salt-water willand decrease district approximately 1,500 In the remaining districts, the area of saltwater by 0.53is approximately to 0.96% and byto0.65 to 0.70% bythe2020 andlayer 2030, intrusion equal that which occurs in Holocene T his respectively trend of changes in the area of saline intrusion intogroundwateris similar to that in the other areas incoastal Ha Tinh In terms of both RCP4.5 and RCP8.5 scenarios, the Conclusion s average for the future periods 2016-2035, 2046-2065, and Saline water intrusion tends to decreasein terms of the two climate 2080-2099 shows that the development groundwater change scenarios considered - RCP4.5 and RCP8.5 - byof 2020 and 2030: saltby 0.53% by 0.65% toIn0.70% 2020 water storage salinity inwill thedecrease research area tois0.96% quiteand complex the by early and 2030, respectively and mid-century, the level of saline intrusion tends to [2] Arlen W Harbaugh (2005), MODFLOW-2005, The U.S Geological Survey Modular Ground-Water Model - the GroundWaterFlow Process, Chapter 16 of Book 6, Modeling techniques, Section A, Ground Water, U.S Department of the Interior and U.S Geological Survey, Reston, Virginia [3] Chunmiao Zheng, P Patrick Wang (1999), MT3DMS: A Modular Three-Dimensional Multispecies Transport Model for Simulation of Advection, Dispersion, and Chemical Reactions of Contaminants in Groundwater Systems, Documentation and User’s Guide, Department of Geological Sciences, University of Alabama, Tuscaloosa [4] Ministry of Natural Resources and Environment (2016), Scenarios for climate change and sea level rise for Vietnam [5] Vietnam Academy for Water Resources (2016), Project “Technical consultancy on hydrological/hydraulic model of Rao Cai river basin and drainage model in the Ha Tinh city, Ha Tinh Province” In terms of both RCP4.5 and RCP8.5 scenarios, the average for the future periods 2016-2035, 2046-2065, and 2080-2099 shows that thedevelopmentof groundwater salinity in theresearch area is quite complex In the early and midcentury, the level of saline intrusion tends to decreaseslightly, and thereafter it Vietnam Journal of Science, increases 88 gradually at the end of the century.December 2018 • Vol.60 Number Technology and Engineering According to the climate change scenario s, at the beginning of the century, rainfall in Ha Tinh increased and so did the reserve of underground water in the province; at the end of the century,the sea level in Ha Tinh will rise ... This trend of changes in the area of saline intrusion into groundwater is similar to that in the other areas in coastal Ha Tinh Area of salinity intrusion in terms of the climate change scenarios... climate climate change scenarios in theof coastal districts of Ha Tinh change scenarios in the coastal districts Ha Tinh province province As shown in Fig 7, the area of salt-water intrusion in the. .. trend of changes in the area of saline intrusion intogroundwateris similar to that in the other areas incoastal Ha Tinh In terms of both RCP4.5 and RCP8.5 scenarios, the Conclusion s average for the