SWAT AND MODFLOW

FOR STUDYING THE IMPACT OF

CLIMATE CHANGE

C.PRADIPAM.Sc (Agrl. Meteorology)

CC – hydrological cycle

Changes in temperature and precipitation - hydrologic

cycle.

Hydrological implications of CC for water resources

Precipitation amount

Global average increase

Marked regional differences

Precipitation frequency and intensity

Less frequent, more intense (Trenberth et al., 2002)

Evaporation and transpiration

Increased total evaporation

Regional complexities due to plant/ atmosphere interactions

Hydrological implications of CC for water resources(cont..)

Changes in run off

Despite global precipitation increases, areas of substantial runoff

decreases

Coastal zones

Saltwater intrusion into coastal aquifers

Severe storm-surge flooding

Water quality

Lower flows, could lead to higher contaminant concentration

Higher flows could lead to greater leaching and sediment transport

Why Modelling is needed?

Model : The tool for understanding the system and its

behavior and for predicting their response.

Tools to use for the assessment: Reference water models

1. SWAT2. MODFLOW3. Aquarius4. Aquacrop5. SWAP (Soil Water Atmosphere Plant)6. ACRU7. RIBASIM8. MIKE MASIN9. WEAP2110. IRAS (Interactive River and Aquifer Simulation)11. . . .

SWAT:

Management decisions on water, sediment, nutrient and

pesticide yields with reasonable accuracy on river basins.

Complex water quality constituents

• Rainfall-runoff, river routing on a daily timestep

MODFLOW

Most widely used numerical groundwater flow model

SWAP- soil-water-atmosphere-plant

• processes at field scale level (growing seasons)

• For water transport and crop growth

• simulates

– transport of water and solutes

– heat in unsaturated/saturated soils

ACRU Model

• Operates on daily time step

• Outputs

– Irrigation scheduling - reservoir operations

– peak discharge , Sediment yield- P, N yields

– flow routing, land use impacts and management changes

– Sensitive climate changes

WEAP21

Seamlessly integrating watershed hydrologic processes with water resources

management

Can be climatically driven

AQUARIS

Economic efficincy criterion requiring the reallocation of stream flows until the

net marginal return in all water uses is equal

Cannot be climatically driven

VOS• Vegetation-overland flow-soil model

• Represents soil vegetation zones with MODFLOW

• Allows for specification of types of soil and vegetation

Data requirement

• Meteorological• Hydrological data • Surface data

– are required for the development and calibration of a mathematical and/or numerical groundwater model.

MODFLOW

First version, 1983, McDonald and Harbaugh.

Written to serve U.S. Geological Survey needs.

Education emphasized.

Mostly written in standard FORTRAN (GMG is C++)

Collaborative open-source development with roots at the USGS

Public domain (Free)

Versions of MODFLOW

MODFLOW

MODFLOW-88

MODFLOW-96

MODFLOW-2000

MODFLOW-2005

Latest version: MODFLOW-2005 (Harbaugh, 2005)

http://water.usgs.gov/nrp/gwsoftware/modflow2005/modflow2005.html

Widely used ground-water flow simulation program Runs on any platform (Windows, Sun, Unix, Linux,

…).

Three-dimensional modelSolves the ground-water flow equation with different

possible properties, boundary conditions and initial

conditions

Advantages• Include numerous facilities for data preparation

• Easy exchange of data in standard form

• Extended worldwide experience

• Continuous development

• Availability of source code and

Disadvantages:

• Surface runoff and unsaturated flow are not included,

• Hence in case of transient problems, MODFLOW can not be

applied if the flux at the groundwater table depends on the

calculated head and the function is not known in advance.

Land surface elevation is not used in MODFLOW, except in the ET package.

MODFLOW

• When properly applied, MODFLOW is the recognized

standard model.

• Ground-water flow within the aquifer is simulated in

MODFLOW using a block-centered finite-difference approach.

• Flows from external stresses such as flow to wells, areal

recharge, evapotranspiration, flow to drains, and flow through

riverbeds can also be simulated.

MODFLOW using a block-centered finite-difference approach.

MT3D (A Modular 3D Solute Transport Model)

• simulating solute transport in complex hydrogeologic settings.

• MT3D is linked with MODFLOW

• Designed specifically to handle advectively-dominated transport problems without the need to construct refined models specifically for solute transport.

FEFLOW

(Finite Element Subsurface Flow System)

Finite-element package for simulating 3D and 2D fluid density-coupled flow, contaminant mass (salinity) and heat transport in the subsurface.

HST3D

(3-D Heat and Solute Transport Model)

simulates ground-water flow and associated heat and solute transport in 3D.

SEAWAT

(Three-Dimensional Variable-Density Ground-Water Flow)

• Developed to simulate variable- density, transient ground-water flow in porous media.

• The source code for SEAWAT was developed by combining MODFLOW and MT3D into a single program that solves the coupled flow and solute-transport equations.

• * MT3D -(A Modular 3D Solute Transport Model )

SUTRA

(2-D Saturated/Unsaturated Transport Model)

• A complete saltwater intrusion and energy transport model.

• A 3-D version of SUTRA has also been released.

SWIM

(Soil water infiltration and movement model)

• Deals with a one-dimensional vertical soil profile which may be vertically in homogeneous but is assumed to be horizontally uniform.

• Used to simulate runoff, infiltration, redistribution, solute transport and redistribution of solutes, plant uptake and transpiration, evaporation, deep drainage and leaching.

Often use MODFLOW through a (Graphical) User Interface

Maps

Model

Results

MODFLOW – user perspective

•BASIC INPUT ITEMS:• Grid

• Time stepping

• Solution parameters

• Hydraulic parameters (includes material properties)

• Boundary Conditions

• Stresses (source-sinks)

• Output options

• ASCII text files

OUTPUT OPTIONSListing file or into a separate file. Complete listing of all input data, drawdown, and budget

data.

• Budget data are printed as a summary in the listing file, and

detailed budget data for all model cells can be written into a

separate file.

• ASCII text files

• Binary files

•Graphical user interface (GUI)

Case studies

•Projected impacts of climate change on farmers’ extraction of

groundwater from crystalline aquifers in South India

•Sylvain Ferrant et al., 2014

• Downscaled GCM data- spatially distributed agro-hydrological

model - MODFLOW

•Projected - climatic extremes create worse GWE shortages

•Areas vulnerable to CC in terms of irrigation apportionment

•Emphasize – importance of accounting for local characteristics

(water harvesting systems and maximal aquifer capacity versus

GWE) in developing measures to cope with CC impacts.

•Seasonal variation in natural recharge of coastal aquifers

•Mollema and Antonellini (2013)

•Temperature data for the period 1960–1990 from LocClim (local

climate estimator) and IPCC SRES A1b scenario

•For 2070–2100 - calculate the potential evapotranspiration with

the Thornthwaite method.

•Potential recharge (difference between precipitation and potential

evapotranspiration) was defined at 12 locations

• SEAWAT model

•Soil and Water Assessment Tool

• Spatial Scale: watershed or river basin

• Data Organization: sub basins or hydrologic response units (HRU’s)

• Time scale: Continuous time model (long term yield model) based on a daily scale

Not for a single event • Data Inputs: weather, soil properties, topography,

vegetation, and land management practices  From the BASINS databases

SWAT – An Overview

SWAT separates soil profiles into 10 layers to model inter and

intra-movement between layers.

The model is applied to each soil layer independently starting

at the upper layer. SWAT soil water routing feature consists of four main pathways:

1. Soil evaporation

2. Plant uptake and transpiration

3. Lateral flow

4. Percolation.

SWAT – An Overview

Soil and Water Assessment Tool (SWAT)

• Inputs:– Precipitation– Max/Min Temperature– Land Use– Soils– Land Management– Topography– Hydrogeology– Weather

http://www.brc.tamus.edu/swat/

• Output:– Daily Streamflow

SWAT is a watershed modeling tool

Summary

Precipitation(Rainfall & Snow)

Evaporation and Transpiration

Infiltration/plant uptake/ Soil moisture redistribution

Surface Runoff

Lateral Flow

Percolation to shallow aquifer

Focus of Presentation

Land-use/management

practices

SWAT

Topography

Soils

Temperature PrecipitationCalibration/Validation

Prioritization(Flow-weighted concentration)

PBIASNSER2

RSR

Point Sources

SWAT Output with Various Sources of Climate Input

Takle et al., 2005

NNR -> RCM -> SWAT-> stream flowGCM -> RCM -> SWAT-> stream flowGHG -> GCM -> RCM -> SWAT -> stream flowStream flow vs. precipitation

SWAT2000: current capabilities and research opportunities in applied

watershed modelling

J. G. Arnold and N. Fohrer, 2005

•To assist water resource managers in assessing the impact of management and

climate on water supplies and non-point source pollution in watersheds and large

river basins.

•Was developed to ‘scale up’ past field-scale models to large river basins.

•Model components include weather, hydrology, erosion/sedimentation, plant

growth, nutrients, pesticides, agricultural management, stream routing and

pond/reservoir routing.

•Current research is focusing on bacteria, riparian zones, pothole topography,

forest growth, channel downcutting and widening, and input uncertainty

analysis.

Climate change impact assessment on hydrology of Indian river basinGosain et al., 2006

• NATCOM - was the first attempt to quantify the impact of the climate change on the water resources of the country

• twelve river basins • detailed analyses on two river basins selected with respect to the extreme drought and

flood conditions predicted on account of the climate change.• spatio-temporal water availability- without incorporating any man-made changes like

dams, diversions, etc.

Percent change in mean annual water balance components

Thank you