378
11. 11enenti
a major determinant of regional hydrology and of the quality of the environment.
Furthermore, extensively irrigated lands in arid zones increases soil wetness and
evaporation significantly over large areas leading to large impacts on the
atmospheric boundary layer and increasing convective activity locally (Wang et
aI., 1993).
In arid environments irrigated agriculture can be either friend or foe of sustainable development and environmental equilibrium (see e.g. Jensen, 1996), with the
outcome depending on how precisely rural planning and water management take
into account hydrological constraints on development. The welfare of people is (or
should be) the dominant driver towards irrigated agriculture, thereby adding
complexity to sustainable land and water management.
All of the above leads to a need for improved monitoring, understanding and
modelling of spatial processes related to irrigation and drainage. The potential
relevance of remote sensing for this purpose is self-evident and the scope of this
chapter is to provide an overview of the significant and specific body of work
accumulated during the last 20 years.
Besides the watershed-oriented issues mentioned above, irrigation also includes
specific management processes requiring a broad range of skills from agrometeorology to administration and management. A first and obvious need is the
capability of assessing, monitoring, understanding and control of water use. For
small irrigation schemes this can be easily accomplished through direct contact
with farmers. For large schemes comprising towns, villages and diverse productive
sectors, experience proves how difficult it is to collect accurate data on actual
water use by· traditional methods. Given the large difference in the water
requirements of cultivated and bare land, the primary need here is the determination of irrigated area, so is not surprising (see Current Applications) that a
dominant share of operational applications relate to this issue. Identification and
mapping of individual crops, although a traditional area of remote sensing and
irrigation studies, is more challenging and less accurate and this is reflected by
literature. Useful information on water use can be obtained by observing specific
spatial patterns such waterlogged or saline areas and linking such patterns with
irrigation and drainage canals.
17.1.1 Current non-remote sensing approaches and limitations.
It is not feasible to compare each type of application (see Current Applications)
with an equivalent non-remote sensing technique. A significant reference might be
provided by considering how irrigated area is determined traditionally. In many
countries farmers hold permanent water rights (assessed in area units). This
provides the basis for water allocation, removing the need for accurate and up-todate information, but often leading to significant mis-allocation of water as actual
irrigated area changes. In a number of countries irrigation fees are assessed on the
basis of irrigated area or of crop type: these data are typically based on statements
by farmers provided to either the Irrigation Authority or the Revenue Service. The
reliability of this information is questioned by many. Another approach is by using
11. 11enenti
a major determinant of regional hydrology and of the quality of the environment.
Furthermore, extensively irrigated lands in arid zones increases soil wetness and
evaporation significantly over large areas leading to large impacts on the
atmospheric boundary layer and increasing convective activity locally (Wang et
aI., 1993).
In arid environments irrigated agriculture can be either friend or foe of sustainable development and environmental equilibrium (see e.g. Jensen, 1996), with the
outcome depending on how precisely rural planning and water management take
into account hydrological constraints on development. The welfare of people is (or
should be) the dominant driver towards irrigated agriculture, thereby adding
complexity to sustainable land and water management.
All of the above leads to a need for improved monitoring, understanding and
modelling of spatial processes related to irrigation and drainage. The potential
relevance of remote sensing for this purpose is self-evident and the scope of this
chapter is to provide an overview of the significant and specific body of work
accumulated during the last 20 years.
Besides the watershed-oriented issues mentioned above, irrigation also includes
specific management processes requiring a broad range of skills from agrometeorology to administration and management. A first and obvious need is the
capability of assessing, monitoring, understanding and control of water use. For
small irrigation schemes this can be easily accomplished through direct contact
with farmers. For large schemes comprising towns, villages and diverse productive
sectors, experience proves how difficult it is to collect accurate data on actual
water use by· traditional methods. Given the large difference in the water
requirements of cultivated and bare land, the primary need here is the determination of irrigated area, so is not surprising (see Current Applications) that a
dominant share of operational applications relate to this issue. Identification and
mapping of individual crops, although a traditional area of remote sensing and
irrigation studies, is more challenging and less accurate and this is reflected by
literature. Useful information on water use can be obtained by observing specific
spatial patterns such waterlogged or saline areas and linking such patterns with
irrigation and drainage canals.
17.1.1 Current non-remote sensing approaches and limitations.
It is not feasible to compare each type of application (see Current Applications)
with an equivalent non-remote sensing technique. A significant reference might be
provided by considering how irrigated area is determined traditionally. In many
countries farmers hold permanent water rights (assessed in area units). This
provides the basis for water allocation, removing the need for accurate and up-todate information, but often leading to significant mis-allocation of water as actual
irrigated area changes. In a number of countries irrigation fees are assessed on the
basis of irrigated area or of crop type: these data are typically based on statements
by farmers provided to either the Irrigation Authority or the Revenue Service. The
reliability of this information is questioned by many. Another approach is by using