GIS Applications in Regional and Global Hydrology

Jay Famiglietti1,2, Stephen Graham1, Corinna Prietzsch1, Karen Mohr1

David Maidment2, Francisco Olivera2, Kwabena Asante2, Mary Lear2

The University of Texas at Austin1Department of Geological Sciences

2Center for Research in Water Resources

Introduction: Jay Famiglietti

GIS-Based Global-Scale Runoff Routing: Jay Famiglietti

GIS Data Layers for Global Hydrologic and Climate System Modeling: Stephen Graham

GIS in Remote Sensing: Corinna Prietzsch

GIS Data Layers for a Regional Hydrologic and Land-Atmosphere Interaction Study: Karen Mohr

Overview

DTM-Based Model forGlobal-Scale Runoff Routing

Francisco OliveraJames FamigliettiKwabena AsanteDavid Maidment

Center for Research in Water Resources

University of Texas at Austin

American Geophysical Union1998 Fall MeetingDecember 6, 1998Paper Number: H71D-11

MotivationCurrently, most global climate models (GCM’s) ...

– … do not have the capability of routing runoff from

the land to the ocean.

– … assume runoff arrives at the ocean instantaneously,

as if flow velocities were infinite (NCAR fully-coupled

land-ocean-atmosphere model - NCAR CSM).

Is flow routing at a global scale worth it?

Runoffon the land

Streamflow into the ocean

Goals

• Determine whether runoff routing has a significant impact on coastline flows by comparing routed vs. unrouted runoff hydrographs.

• Explore a new method for runoff routing that …– ... exploits the availability of high resolution

global DTM’s.– … could be incorporated in a global climate

model (GCM) like NCAR’s CSM.

Source-to-Sink Routing Model

• Defines sources (or runoff producing units) where runoff enters the surface water system, and sinks (or runoff receiving units) where runoff leaves the surface water system.

• Calculates hydrographs at the sinks by adding the contribution of all sources in the drainage area.

• A response function is used to represent the motion of water from the sources to the sinks.

Sinks

• A 3°x3° mesh is used to subdivide the whole globe into “square” boxes.

• A total of 132 sinks were identified for the African continent (including inland catchments like theLake Chad Basin).

Drainage Area of the Sinks

• The drainage area of each sink is delineated using raster-based GIS functions applied to GTOPO30.

• GTOPO30 (EROS Data Center of the USGS, Sioux Falls, ND) is digital elevation data with an approximate resolution of 1 Km x 1 Km.

Land Boxes• A 0.5°x0.5° mesh is used

to subdivide each drainage area into land boxes.

• 0.5° land boxes allow the modeler to capture the geomorphology of the hydrologic system.

• For the Congo River basin, 1379 land boxes were identified.

Runoff Boxes (T42 Data)

• Runoff data has been calculated using NCAR’s CCM3.2 GCM over a 2.8125° x 2.8125° mesh (T42).

• For the Congo River basin, 69 runoff boxes were identified.

Sources

• Sources are obtained by intersecting:

– drainage area of the sinks

– land boxes

– runoff boxes

• Number of sources:

– Congo River basin: 1954

– African continent: 19170

Flow Length to the Sinks

• Flow-length is calculated for each GTOPO30 cell by using raster-based GIS functions, and then averaging the resulting values over the source area.

• The flow time from a source to a sink is calculated by dividing the flow length by the (uniformly distributed) flow velocity.

Distance-Area Diagrams

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Global Runoff

According to NCAR’s CCM3.2 Global Climate Model (GCM)

Routing Algorithm

For source j: tj = Lj/v

For sink i: Qi = Aj Rj(t)*uj(t) exp(-k tj)

where:tj = flow timeLj = flow lengthv = flow velocityQi = flowAj = areaRj(t) = runoff time seriesuj(t) = response functionk = loss coefficient

Routed vs Unrouted Hydrographs

Assuming v = 0.3 m/s and k = 0

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Routed Unrouted

Source-to-Sink vs. Cell-to-Cell

Assuming v = 0.3 m/s and k = 0

Source-to-sink

Cell-to-cell

Conclusions (1)• A DTM-based methodology for global-scale flow routing

has been developed. The methodology is independent of the geographic location and spatial resolution of the data.

• The need for accounting for flow delay in the landscape, especially in large watersheds, became obvious after comparing routed vs. unrouted hydrographs.

• Because the spatial distribution of the model parameters (e.g., flow velocity, v, and losses coefficient, k) is unknown, uniformly distributed values were assumed.

Conclusions (2)

• The model takes advantage of “high” resolution terrain data and is able to produce results consistent with “low” resolution global data used for climate models.

• The model produces similar results when compared to cell-to-cell routing models, but has the advantage of being independent of the terrain discretization.

Five-Minute, 1/2-Degree, and 1-Degree Data Sets of Continental Watersheds and River Networks for Use in Regional and Global Hydrologic and Climate System Modeling

Studies

Stephen Graham1

Jay Famiglietti1,2

David Maidment2

The University of Texas at Austin1Department of Geological Sciences

2Center for Research in Water Resources

Introduction

9 Data Layers 3 Resolutions

1) Land/sea mask2) Flow direction information3) Flow accumulation information4) River delineation5) 55 Large watersheds6) Internally draining regions7) 19 large-scale drainage regions8) 19 large-scale drainage regions extended to water bodies9) Lake delineation

5-minute1/2-degree

1-degree

Additional runoff data

The National Geophysical Data Center TerrainBase Global DTM Version 1.0

[Row et al., 1995]

The CIA World Data Bank II [Gorny and Carter, 1987]

Data and Analysis Methods

1) Determination of a land/sea mask

2) Geolocation or ‘burning in’ of rivers

3) Filling of artificial depressions

4) Calculation of flow directions

5) Calculation of flow accumulations

6) Selection and delineation of rivers

7) Selection and delineation of watersheds

8) Lake Delineation

1) Determination of a land/sea mask

TerrainBase Land Only

2) Geolocation or ‘burning in’ of rivers

Digitized rivers from the CIA World Data Bank II are extracted and gridded.

The elevations of grid cells that correspond to the gridded rivers are decreased by an appropriate amount, thereforegiving an added incentive for water to follow the digitized paths.

This process improves the location of rivers in flat areas,as well as mountainous areas where narrow canyons may be averaged out in the DEM.

3) Filling of artificial depressions

Grid: FILL elev_grid fill_grid SINK

Artificial and natural depression are both present in DEMs.In order for river channels to flow to their mouth at a water body, the course of the river must follow a monotonicallydecreasing path, as is defined by the flow direction grid.Consequently, sinks must be eliminated except at terminal points for water accumulation, such as inland seas.Certain sinks may also be selected to remain sinks, either manually or by using automated procedures which take into consideration such things as the depth and area of the sink.

Stream channel comparison

Filled DEMRivers burned into

DEM and then filled

4,5) Calculation of flow directions and accumulations

Grid: fdr_grid = FLOWDIRECTION ( fill_grid )

Grid: fac_grid = FLOWACCUMULATION ( fdr_grid )

Grayscale flow direction map

Grayscale flow accumulation map

6) Selection and delineation of rivers

Grid: riv_grid = CON ( fac_grid >= 3500 , 1 )

Flow accumulation thresholds for different sized analysis regions

FAC Threshold = 1000 FAC Threshold = 100

7) Selection and delineation of watersheds

Create a source_grid by intersecting coasts with riversGrid: wshed_grid = WATERSHED ( dir_grid , source_grid )

7a) Selection and delineation of internally draining areas

Create a grid of the sinks that should remain sinks, which in turn are used as source cells for WATERSHED

7b) Selection and delineation of 19 global drainage regions

A coast_grid can be divided into the desired sections and used as source cells for WATERSHED

7c) Extension of 19 global drainage regions to include water bodies

EUCALLOCATION can be used to extend areas of the 19 regions to the oceans by assigning the closest existing value.

8) Lake Delineation

Lakes are derived from CIA World Data Bank II

Runoff DataTop 10 of 55 rivers by total runoff

River Name Country Lat. Lon. Runoff (km3)

Amazon Brazil 0 310 6084Zaire(Congo) Zaire -6 12.5 1285Ganges/Brahmaputra Bangladesh 22 91 1072Orinoco Venezuela 9 299 976Chang Jiang (Yangtze) China 31.5 122 910Yenisei Russia 72 82 579Parana (Plata) Argentina -35 303 517Mississippi USA 29 271 514Lena Russia 73 127 514Mekong Vietnam 10 106 468

Changing resolutions

The elevations are averaged over 1/2- and 1-degree boxesto obtain the coarser resolution 1/2- and 1-degree DEMs from the original 5-minute data.

The same processes from above are then carried out at each new resolution.

Effects of Resolution 1

5-minute

1/2-degree

1-degree

Coarsening of geographic features

Effects of Resolution 2

5-minute

1/2-degree

1-degree

Narrow features altered and merged with others