GIS Applications in Regional and Global Hydrology Jay Famiglietti 1,2, Stephen Graham 1, Corinna Prietzsch 1, Karen Mohr 1 David Maidment 2, Francisco Olivera 2, Kwabena Asante 2, Mary Lear 2 The University of Texas at Austin 1 Department of Geological Sciences 2 Center 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 for Global-Scale Runoff Routing Francisco Olivera James Famiglietti Kwabena Asante David Maidment Center for Research in Water Resources University of Texas at Austin American Geophysical Union 1998 Fall Meeting December 6, 1998 Paper Number: H71D-11

Motivation Currently, 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? Runoff on 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 the Lake 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 ° x ° 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 Amazon River Basin Congo River Basin MacKenzie River Basin Yangtze River Basin

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

Routing Algorithm For source j: t j = L j /v For sink i: Q i =  A j R j (t)*u j (t) exp(-k t j ) where: t j = flow time L j = flow length v= flow velocity Q i = flow A j = area R j (t)= runoff time series u j (t)= response function k= loss coefficient

Routed vs Unrouted Hydrographs Assuming v = 0.3 m/s and k = 0 Amazon River Yangtze River Congo River MacKenzie River RoutedUnrouted

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 Graham 1 Jay Famiglietti 1,2 David Maidment 2 The University of Texas at Austin 1 Department of Geological Sciences 2 Center for Research in Water Resources

Introduction

9 Data Layers 3 Resolutions 1) Land/sea mask 2) Flow direction information 3) Flow accumulation information 4) River delineation 5) 55 Large watersheds 6) Internally draining regions 7) 19 large-scale drainage regions 8) 19 large-scale drainage regions extended to water bodies 9) Lake delineation 5-minute 1/2-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, therefore giving 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 monotonically decreasing 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 DEM Rivers 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 = 1000FAC Threshold = 100

7) Selection and delineation of watersheds Create a source_grid by intersecting coasts with rivers Grid: 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 Data Top 10 of 55 rivers by total runoff

Changing resolutions The elevations are averaged over 1/2- and 1-degree boxes to 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