Evapotranspiration Estimates from Remote Sensing for Irrigation Water Management - Satellite-based Applications on Climate Change - page 188

13.1 Introduction

Global warming is expected to change not only atmospheric temperature but also
climatic variables such as humidity, precipitation, and net terrestrial solar radiation
(IPCC 2007 ). Also predicted are an intensified hydrological cycle and altered
evapotranspiration, with implications for irrigated crops, ecosystems services, and
feedback to the regional and global climate (Jung et al. 2010 ).
With increasing demands on limited water supplies, exacerbated by a changing
climate, understanding when, where, and how much water is consumptively used is
increasingly important. In many arid regions of the world, irrigated agriculture is
the dominant water user, and monitoring irrigation system performance and
improving efficiency of water use are integral to sustainable water management.
Physically based actual crop evapotranspiration (ET) from remote sensing can be
used to measure water use from all sources, including precipitation and irrigation
from both surface and groundwater. The actual ET is measured for each pixel of each
satellite image acquired during an irrigation season, yielding spatially and temporally
distributed maps of ET. These products can then be used in GIS processing with
spatial analyses to produce a range of statistics, reports, visualizations, and other
results for use by water resources planners, managers, and irrigators. In Morocco, for
example, groundwater policy and regulation are not well established, and reliable
data on the location and quantity of groundwater use are not available. Satellite-
derived ET maps, combined with surface water supply data, can be used to analyze
the efficiency of irrigation water supply from all sources and to estimate the contri-
bution of groundwater.
The spatial distribution and availability of water are critical for sustainable
development of modern societies and for maintaining and protecting natural
ecosystems. Sufficient water supplies are required for agricultural, municipal,
industrial, recreational, and other uses. Economic progress often depends on devel-
opment of water supply infrastructures that store and distribute surface waters and
exploit underground aquifers.

13.2 Objective and Approach

Morocco has invested heavily in water supply infrastructure and large-scale irriga-
tion systems to secure water for urban and agricultural demands; however, these
supply oriented measures were not coupled with policies and development aimed at
sustainable water management and conservation. Recently, the World Bank and
government of Morocco formulated the $115 M Oum Er Rbia Irrigated Agriculture
Modernization Project (MA Project) to help participating farmers increase produc-
tivity and, simultaneously, promote more sustainable use of irrigation water to
overcome current and future water deficits. This irrigation modernization program
seeks to conserve water by converting to more efficient irrigation technology and to
relieve unsustainable groundwater abstraction rates. The surface water resources of
the irrigation schemes are monitored and regulated by the government of Morocco;