Global Hydrology Francisco Olivera Center for Research in Water Resources University of Texas at Austin 19 th ESRI International User Conference GIS Hydro 99 - Introduction to GIS Hydrology July 25, San Diego, California

The Team zKwabena Asante zMarcia Branstetter zJames Famiglietti zMary Lear zDavid Maidment zFrancisco Olivera Researchers celebrating after the successful run of an Avenue script. (Picture taken from Ajax – Amsterdam The Official Web Site).

Overview zSoil water balance yGIS-based data development. yExternally run soil water balance model. yGIS-based presentation of results. zFlow routing yGIS-based terrain and topologic data development. yExternally run flow routing model. yExternal presentation of results.

Soil Water Balance Model Precipitation: P Evaporation: E Soil moisture: w Surplus: S Temperature: T Net Radiation: R n

Soil Water Balance Model Given: w fc : soil field capacity (mm) w pwp : soil permanent wilting point (mm) P : precipitation (mm) T : temperature (°C) R n : net radiation (W/m 2 ) Evaporation: Soil moisture and surplus: Calculated: w : actual soil moisture (mm) S : water surplus (mm) E : actual evaporation (mm) E p : potential evaporation (mm)

Global Data Precipitation and temperature data, at 0.5° resolution, by D. Legates and C. Willmott of the University of Delaware. Net radiation data, at 2.5° resolution, by the Earth Radiation Budget Experiment (ERBR). Soil water holding capacity, at a 0.5° resolution, by Dunne and Willmott. Precipitation (Jan.)Temperature (Jan.) Net Radiation (Jan.)Soil Water Holding Capacity

Monthly Surplus February May August November Period between storms: 3 days.

Monthly Surplus 10 days between storms 1 day between storms3 days between storms 30 days between storms Effect of disaggregation of monthly precipitation into multiple storms.

Flow Routing Models zCell-to-cell zElement-to-element zSource to sink Source Flow-path Sink Cell Sub-Basin Junction Reach Sink

Cell-to-Cell Model zSets a mesh of cells on the terrain and establishes their connectivity. zRepresents each cell as a linear reservoir (outflow proportional to storage). One parameter per cell: residence time in the cell. zFlow is routed from cell-to-cell and hydrographs are calculated at each cell. K1K1 K2K2 K3K3 K4K4 K5K5

Mesh of Cells zCongo River basin subdivided into cells by a °  ° mesh (T42). zWith this resolution, 69 cells were defined.

Low Resolution Flow Direction zLow resolution flow directions determined from high resolution flow directions. zThe algorithm supports: yCells that are not aligned with the DEM. yThrough-the-side and through-the-corner flow directions. FAc 3 FAc 4 B C D 12 3 FAc 1 A FAc 2 4

Low Resolution Stream Network zHigh resolution flow directions (1 Km DEM cells) are used to define low resolution flow directions (0.5° cells). zNiger River Basin stream network based on low resolution flow directions (0.5° cells).

Cell Length zThe cell length is calculated as the length of the flow path that runs from the cell outlet to the receiving cell outlet. FAc 3 FAc 4 B C D 12 3 FAc 1 A FAc 2 4

Element-to-Element Model zDefines hydrologic elements (basins, reaches, junctions, reservoirs, diversions, sources and sinks) and their topology. zElements are attributed with hydrologic parameters extracted from GIS spatial data. zFlow is routed from element-to- element and hydrographs are calculated at all elements. zDifferent flow routing options are available for each hydrologic element type. Sub-Basin Junction Reach Sink Sub-Basin

Sub-Basins and Reaches zCongo River basin subdivided into sub-basins and reaches. zSub-basins and reaches delineated from digital elevation models (1 Km resolution). zStreams drain more than 50,000 Km 2. Sub-basin were defined for each stream segment.

Hydrologic System Schematic zHydrologic system schematic of the Congo River basin as displayed by HEC-HMS.

Hydrologic System Schematic zDetail of the schematic of the Congo River basin.

Source-to-Sink Model zDefines sources where surplus enters the surface water system, and sinks where surplus leaves the surface water system. zFlow is routed from the sources directly to the sinks, and hydrographs are calculated at the sinks only. zA response function is used to represent the motion of water from the sources to the sinks. Source Flow-path Sink Source Flow-path

Sinks zSinks are defined at the continental margin and at the pour points of the inland catchments. zUsing a 3°x3° mesh, 132 sinks were identified for the African continent (including inland catchments like Lake Chad).

Drainage Area of the Sinks zThe drainage area of each sink is delineated using raster- based GIS functions applied to a 1-Km DEM (GTOPO30). GTOPO30 has been developed by the EROS Data Center of the USGS, Sioux Falls, ND.

Land Boxes zLand boxes capture the geomorphology of the hydrologic system. zA 0.5°x0.5° mesh is used to subdivide the terrain into land boxes. zFor the Congo River basin, 1379 land boxes were identified.

Surplus Boxes (T42 Data) zSurplus boxes are associated to a surplus time series. zSurplus data has been calculated using NCAR’s CCM3.2 GCM model over a ° x ° mesh (T42). zFor the Congo River basin, 69 surplus boxes were identified.

Sources zSources are obtained by intersecting: ydrainage area of the sinks yland boxes ysurplus boxes zNumber of sources: yCongo River basin: 1,954 yAfrican continent: 19,170

Response Function zAdvection (pure translation) zAdvection and dispersion (translation and flow attenuation) Source Flow-path Sink t t t t Q sink =  Q source S source Q source S source Q source

Source-to-Sink vs. Cell-to-Cell Source-to-sink Cell-to-cell zCongo River at the Atlantic Ocean zSurplus from NCAR’s CCM3.2 GCM model zv = 0.3 m/s

Source-to-Sink vs. Element-to-Element Source-to-sink Cell-to-cell zCongo River at the Atlantic Ocean zInstantaneous and uniform surplus of 0.01 m zv = 0.3 m/s and D = 2000 m 2 /s

Nerd Stuff zAccounting of spatial distribution of flow velocities and flow attenuation coefficients. zAccounting for losses due to infiltration and evaporation. zAccounting for controlled and uncontrolled reservoirs, and floodplain storage. zRelative importance of hydrodynamic dispersion (flow attenuation) vs. advection (pure translation). zRelative importance of hydrodynamic dispersion vs. geomorphologic dispersion in large hydrologic systems.