90
R. Kimura
by 60 km. Irrigation farming has recently extended, and the number of wells in 2012
had increased by about 30% from that in 2008. Efficient irrigation farming is crucial
to establish the sustainable water use (Kato et al. 2010).
This chapter focuses on climate features of Dakhla Oasis, which are important factors to consider when evaluating the sustainable water use in oasis regions.
First, the climate history of the Western Desert of Egypt is presented, followed
by a description of current conditions. These climatic features are then examined
by using synoptic meteorological data from 2007 to 2016, and the climatic differences between Dakhla and Kharga Oases are discussed. Recommendations for use of
improved remote-sensing resources to monitor climate in this area are also presented.
2 Climatic History of the Western Desert of Egypt
About 20,000 years ago, during the coldest period of the last ice age, the monsoon
season weakened in the tropical area, which facilitated a dry climate. Tropical Africa
also experienced a largely dry climate, and the boundary of the Sahara was several
hundred kilometers south of its present location. The desert spread into the tropical
area during this era (Shinoda 2002).
Geological, archaeological, and paleoclimatic reconstructions indicate that the
eastern Saharan climate during the early-to-mid Holocene (9,300–4,500 years BP)
was much wetter than it is today (Salman et al. 2010) because an intertropical convergence zone (ITCZ) existed farther north as compared with the present day. The ITCZ
is a belt of converging trade winds and rising air that encircles the Earth near the
equator and produces heavy rainfall. Strong monsoons from the Indian and Atlantic
oceans contribute a large quantity of water vapor that was transported to the Saharan
ITCZ. In addition, the transpiration of Saharan vegetation actively supplied even
more water vapor to the atmosphere.
The Saharan climate had wet peaks from 9,000 to 8,000 and from 7,000 to
5,000 years ago. During these periods, there was a large amount of rainfall in the
Sahara, which was covered by savanna and steppe vegetation. These wet phases
were characterized by the rapid onset of a mosaic of freshwater lake and swamp
formations, which led to groundwater recharge of the Nubian aquifer in the eastern
Sahara Desert (Pachur and Hoelzmann 2000). The Dakhla Oasis region was also
once dominated by a vast lake. Neolithic rock carvings indicate that various animals,
including elephants, zebras, and giraffes, occupied its shores. During these periods,
the oasis would have been similar to the African savanna (https://egyptsites.wordpr
ess.com/2009/03/10/introduction-to-dakhla-oasis/).
A humid period (the Green Sahara era) in tropical Africa around the Sahara
to Sahel regions ended about 4,500 years ago, when climate cooling began on a
global scale. Since then, minor wet and dry periods have cycled, with the present
cycle representing a drier period. From a long-term perspective, the present Sahara,
including Dakhla Oasis, is in the middle of an aridification period (Shinoda 2002).
Based on analyses of fossil diatoms in Lake Qarun, Egypt, there was a sudden change
R. Kimura
by 60 km. Irrigation farming has recently extended, and the number of wells in 2012
had increased by about 30% from that in 2008. Efficient irrigation farming is crucial
to establish the sustainable water use (Kato et al. 2010).
This chapter focuses on climate features of Dakhla Oasis, which are important factors to consider when evaluating the sustainable water use in oasis regions.
First, the climate history of the Western Desert of Egypt is presented, followed
by a description of current conditions. These climatic features are then examined
by using synoptic meteorological data from 2007 to 2016, and the climatic differences between Dakhla and Kharga Oases are discussed. Recommendations for use of
improved remote-sensing resources to monitor climate in this area are also presented.
2 Climatic History of the Western Desert of Egypt
About 20,000 years ago, during the coldest period of the last ice age, the monsoon
season weakened in the tropical area, which facilitated a dry climate. Tropical Africa
also experienced a largely dry climate, and the boundary of the Sahara was several
hundred kilometers south of its present location. The desert spread into the tropical
area during this era (Shinoda 2002).
Geological, archaeological, and paleoclimatic reconstructions indicate that the
eastern Saharan climate during the early-to-mid Holocene (9,300–4,500 years BP)
was much wetter than it is today (Salman et al. 2010) because an intertropical convergence zone (ITCZ) existed farther north as compared with the present day. The ITCZ
is a belt of converging trade winds and rising air that encircles the Earth near the
equator and produces heavy rainfall. Strong monsoons from the Indian and Atlantic
oceans contribute a large quantity of water vapor that was transported to the Saharan
ITCZ. In addition, the transpiration of Saharan vegetation actively supplied even
more water vapor to the atmosphere.
The Saharan climate had wet peaks from 9,000 to 8,000 and from 7,000 to
5,000 years ago. During these periods, there was a large amount of rainfall in the
Sahara, which was covered by savanna and steppe vegetation. These wet phases
were characterized by the rapid onset of a mosaic of freshwater lake and swamp
formations, which led to groundwater recharge of the Nubian aquifer in the eastern
Sahara Desert (Pachur and Hoelzmann 2000). The Dakhla Oasis region was also
once dominated by a vast lake. Neolithic rock carvings indicate that various animals,
including elephants, zebras, and giraffes, occupied its shores. During these periods,
the oasis would have been similar to the African savanna (https://egyptsites.wordpr
ess.com/2009/03/10/introduction-to-dakhla-oasis/).
A humid period (the Green Sahara era) in tropical Africa around the Sahara
to Sahel regions ended about 4,500 years ago, when climate cooling began on a
global scale. Since then, minor wet and dry periods have cycled, with the present
cycle representing a drier period. From a long-term perspective, the present Sahara,
including Dakhla Oasis, is in the middle of an aridification period (Shinoda 2002).
Based on analyses of fossil diatoms in Lake Qarun, Egypt, there was a sudden change