7 Land-use and Catchment Characteristics
B.G.H. Gorte
International Institute for Aerospace Survey and Earth Sciences (lTC),
Enschede, the Netherlands
7.1 Introduction
Vegetative cover or land cover influences hydrological processes in various ways.
Interception and transpiration is a loss or sink term in the water balance of a catchment, and evapotranspiration losses have been shown to influence rainfall in downwind direction at regional scale (Savenije, 1995). The results of a great many paired
catchment experiments have shown that evapotranspiration losses decrease in the
following order; conifers, deciduous hardwoods/mixed hardwood, shrub (Bisch and
Hewlett, 1982). Thus, spectral cover classifications allow the estimation of relative
water losses.
A major step forward is the ability to calculate the actual evapotranspiration of
each pixel over large areas, as related to the land cover, using multi-spectral and
thermal data (Bastiaansen, 1998). See also Chap. 8.
The well known Runoff Curve Numbers method of the U.S. Soil Conservation
Service (SCS) uses a hydrologic vegetation condition, combined with a soil description, for daily runoff estimation from rainfall. Soil units can be combined in a
GIS with remotely sensed vegetation classes to map the curve numbers.
The rarity of overland flow under dense vegetation in temperate climates, often
leading to saturation overland flow and piston flow has been described by many
authors e.g. Ward and Robinson (1989). In contrast, poor vegetation on sloping
lands usually could lead to rapid direct runoff. In smaller catchments vegetation
delays runoff caused by high intensity rainfall bursts, resulting in lower peak runoff
rates. The effects in larger catchments is still a matter of debate (Bruynzeel, 1990).
Soil erosion rates are strongly governed by vegetation. Dense vegetation prevents
rain-splash, increases infiltration and provides vegetal retardance to overland flow.
Hence, land cover classes, as determined by remote sensing, have an implicit hydrological significance in terms of water yield, peak flows and soil erosion. All
available catchment data show that deforestation leads to highly increased sediment
yields. Upstream deforestation can also lead to increased bedload, which may cause
downstream damages in cultivated flood plains (Meijerink and Maathuis, 1997).
Vegetation can also influence water quality, as well as the observations of contaminated throughfall under pines in humid temperate regions with air pollution,
which ultimately affects the water balance. As discussed in Chap. 14, nature of the
vegetation and unsaturated zone conditions determine whether or not the vegetative
G. A. Schultz et al. (eds.), Remote Sensing in Hydrology and Water Management
© Springer-Verlag Berlin Heidelberg 2000
B.G.H. Gorte
International Institute for Aerospace Survey and Earth Sciences (lTC),
Enschede, the Netherlands
7.1 Introduction
Vegetative cover or land cover influences hydrological processes in various ways.
Interception and transpiration is a loss or sink term in the water balance of a catchment, and evapotranspiration losses have been shown to influence rainfall in downwind direction at regional scale (Savenije, 1995). The results of a great many paired
catchment experiments have shown that evapotranspiration losses decrease in the
following order; conifers, deciduous hardwoods/mixed hardwood, shrub (Bisch and
Hewlett, 1982). Thus, spectral cover classifications allow the estimation of relative
water losses.
A major step forward is the ability to calculate the actual evapotranspiration of
each pixel over large areas, as related to the land cover, using multi-spectral and
thermal data (Bastiaansen, 1998). See also Chap. 8.
The well known Runoff Curve Numbers method of the U.S. Soil Conservation
Service (SCS) uses a hydrologic vegetation condition, combined with a soil description, for daily runoff estimation from rainfall. Soil units can be combined in a
GIS with remotely sensed vegetation classes to map the curve numbers.
The rarity of overland flow under dense vegetation in temperate climates, often
leading to saturation overland flow and piston flow has been described by many
authors e.g. Ward and Robinson (1989). In contrast, poor vegetation on sloping
lands usually could lead to rapid direct runoff. In smaller catchments vegetation
delays runoff caused by high intensity rainfall bursts, resulting in lower peak runoff
rates. The effects in larger catchments is still a matter of debate (Bruynzeel, 1990).
Soil erosion rates are strongly governed by vegetation. Dense vegetation prevents
rain-splash, increases infiltration and provides vegetal retardance to overland flow.
Hence, land cover classes, as determined by remote sensing, have an implicit hydrological significance in terms of water yield, peak flows and soil erosion. All
available catchment data show that deforestation leads to highly increased sediment
yields. Upstream deforestation can also lead to increased bedload, which may cause
downstream damages in cultivated flood plains (Meijerink and Maathuis, 1997).
Vegetation can also influence water quality, as well as the observations of contaminated throughfall under pines in humid temperate regions with air pollution,
which ultimately affects the water balance. As discussed in Chap. 14, nature of the
vegetation and unsaturated zone conditions determine whether or not the vegetative
G. A. Schultz et al. (eds.), Remote Sensing in Hydrology and Water Management
© Springer-Verlag Berlin Heidelberg 2000