Evapotranspiration Estimates from Remote Sensing for Irrigation Water Management - Satellite-based Applications on Climate Change - page 190

was recognized in Morocco's Plan Maroc Vert (PMV), or Green Plan, the country's
strategy to transform its agriculture sector.
As a whole, the Mediterranean is expected to be one of the world's regions most
affected by future climate change, with increasing temperature and decreasing
availability of water resources (Hulme et al. 2000 ; Ragab and Prudhomme 2002 ;
Agoumi 2003 ; El Ghissassi 2005 ). Morocco has experienced frequent and lasting
drought over the past several decades, demonstrating its vulnerability to irrigation
water scarcity and threatening livelihoods of farmers and nomad families (e.g.,
Chaouki et al. 1995 ). Rainfall predictions in climate assessments and studies of the
highly diverse river basins in Morocco and the surrounding region are inconsistent,
but these studies consistently predict higher temperatures in the region. Born et al.
( 2008a , b ) studied present and future climate variability of northwestern Africa
using IPCC AR4 data and concluded that the region will continue to experience
drying and warming trends in the future. Driouech et al. ( 2010 ) compared more than
ten RCM outputs over Morocco, all of which showed a decrease in precipitation and
a change in occurrence and distribution of extreme events for the future
(2021-2050). Using the Weather Research and Forecast (WRF) model with IPCC
AR4 GCM output as forcing fields, Patricola and Cook ( 2010 ) simulated Morocco
and North Africa present (1981-2000) and future (2081-2100) climate variation.
Based on their results, they predicted little change in future precipitation and an
increase of 5 C in future temperature.
Recent decreases in precipitation have reduced water available for irrigation
across the country, particularly in the Oum Er Rbia basin. Half of Morocco's large-
scale irrigation systems are in this basin, which produces much of the nation's
crops. However, agricultural production is constrained by water rationing, as
irrigation agencies have distributed, on average, only 60% of the necessary water
over the last decade. Farmers have made up for this reduction in surface water by
using groundwater (Bennani et al. 2001 ), and as a result, water-table levels are
declining at an alarming rate in the Oum Er Rbia basin. Quantitative estimates of
the potential impacts of climate change on Morocco's water resources suggest a
decline of 10-15% of the renewable surface water and groundwater by the year
2020 (Bennani et al. 2001 ).

13.4 Methodology for Estimating Evapotranspiration

13.4.1 Introduction to METRIC

Satellite data are ideally suited for deriving spatially continuous fields of ET using
energy balance techniques. Mapping EvapoTranspiration at high Resolution with
Internalized Calibration (METRIC ) is a satellite-based image-processing tool for

calculating ET as a residual of the energy balance at the earth's surface. METRIC
can function as an operational model for producing maps of ET for regions smaller
than a few hundred kilometers in scale and at high resolution and typically uses
Landsat imagery having 30-m resolution in the short wave and 60-120-m resolution

™