processed a complete set of all Landsat images for land use/land cover changes,
which are readily available for time series viewing over the Internet.
Table 2 provides only a selection of existing systems; many other land observation satellites are in orbit. The specifics listed in Table 2 are important when
choosing imagery for a specific application. Larger pixel sizes facilitate faster
processing, especially with analyses over large areas. However, a larger pixel size
means that the land use spatial detail within that pixel is more likely coarser, and it
represents a mixture of land uses or land covers, especially in urban areas.
5 Significance of Land Use/Land Cover Mapping
for Hydrologic Studies
Land use impacts hydrology largely through its influence upon the natural hydrologic cycle. Vegetated surfaces, especially during the growing season, will redirect
rainfall through the ability of leaves, branches, and trunks to intercept raindrops and
to delay water movement to the soil surface. Forest soils act like sponges, retaining
water so that it is slowly released to groundwater or to flow to streams and rivers
over days, weeks, and months. Open, grassy surfaces likewise capture and slow the
movement of water and retain soil moisture. In contrast, pavement and compacted
or indurated soils impede infiltration and increase surface runoff. Runoff from
impervious surfaces consequently flow to streams, rivers, and storm sewers and
contribute to flooding and contamination of surface waters.
5.1 Land Use and Curve Numbers
Land use impact is significant for hydrologic analysis because it is a key variable in
hydrologic models that predict surface runoff from precipitation events. In traditional hydrologic analysis developed by the USDA Natural Resources Conservation
Service (NRCS), this relationship is described by the runoff curve number (CN), an
empirical approximation of the runoff from a precipitation event in a specific
drainage basin.
Curve numbers have been derived for a variety of surfaces and categorized by
climate and by land use (both broadly and specifically defined) (Table 3) [43]. For
each drainage area examined, analysts examine aerial imagery (often aerial photography, although uses of other forms of imagery may soon increase as their
availability increases) to characterize surface conditions and hydraulic properties
of local land cover, on a parcel-by-parcel basis. Analysts select curve numbers for
each parcel of interest using methods outlined by NRCS, including:
• Land use (from designated classes)
• Hydrologic soil group, defined to identify hydrologic behavior of local soils
(as selected from tables that represent soil units)
16
T.E. Parece and J.B. Campbell
which are readily available for time series viewing over the Internet.
Table 2 provides only a selection of existing systems; many other land observation satellites are in orbit. The specifics listed in Table 2 are important when
choosing imagery for a specific application. Larger pixel sizes facilitate faster
processing, especially with analyses over large areas. However, a larger pixel size
means that the land use spatial detail within that pixel is more likely coarser, and it
represents a mixture of land uses or land covers, especially in urban areas.
5 Significance of Land Use/Land Cover Mapping
for Hydrologic Studies
Land use impacts hydrology largely through its influence upon the natural hydrologic cycle. Vegetated surfaces, especially during the growing season, will redirect
rainfall through the ability of leaves, branches, and trunks to intercept raindrops and
to delay water movement to the soil surface. Forest soils act like sponges, retaining
water so that it is slowly released to groundwater or to flow to streams and rivers
over days, weeks, and months. Open, grassy surfaces likewise capture and slow the
movement of water and retain soil moisture. In contrast, pavement and compacted
or indurated soils impede infiltration and increase surface runoff. Runoff from
impervious surfaces consequently flow to streams, rivers, and storm sewers and
contribute to flooding and contamination of surface waters.
5.1 Land Use and Curve Numbers
Land use impact is significant for hydrologic analysis because it is a key variable in
hydrologic models that predict surface runoff from precipitation events. In traditional hydrologic analysis developed by the USDA Natural Resources Conservation
Service (NRCS), this relationship is described by the runoff curve number (CN), an
empirical approximation of the runoff from a precipitation event in a specific
drainage basin.
Curve numbers have been derived for a variety of surfaces and categorized by
climate and by land use (both broadly and specifically defined) (Table 3) [43]. For
each drainage area examined, analysts examine aerial imagery (often aerial photography, although uses of other forms of imagery may soon increase as their
availability increases) to characterize surface conditions and hydraulic properties
of local land cover, on a parcel-by-parcel basis. Analysts select curve numbers for
each parcel of interest using methods outlined by NRCS, including:
• Land use (from designated classes)
• Hydrologic soil group, defined to identify hydrologic behavior of local soils
(as selected from tables that represent soil units)
16
T.E. Parece and J.B. Campbell