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Hydrological Sciences

Imaggeo on Mondays: Mesopotamia, the ancient land between rivers

Mesopotamia, an area rich in history and considered as the cradle of civilisation, with the first populations establishing themselves in the region some 6000 years ago,lies between two great rivers: the Euphrates and the Tigris. The ancient territory spans areas of modern-day Iraq, Kuwait, the northeastern section of Syria and small sections of southeastern Turkey and southwestern Iran.

The history of Mesopotamia is intrinsically linked to the great rivers which define it. From changes of the river themselves (autogenic), through to non-living environmental factors (known as allogenic) and human activities, the rivers respond to a wide range of processes by changing their courses and forming new waterways.

However, keeping track of the river’s changing paths during their long histories can be tricky. Based on a common assumption made by archaeological studies of the Mesopotamian floodplain, where periods of activity of a river channel are considered to be closely linked to the ages of archaeological settlements, Jaafar H. Jotheri, (a PhD researcher at the University of Durham, UK), was able to study the history of the two rivers.

Most of the identified ancient settlements in the region are thought to have been established near active channels. “Therefore, the existence of settlements in certain areas is a good indication of the probability of the existence of a river close to the site and vice versa,” explains Jaafar. “Not only that, the ages of a settlement can give a suggested age during which a particular river channel was active,” he adds.

Cuneiform script, a style of writing which involved pressing a stylus into soft clay tablets and making indentations representing word-signs, was widely used in ancient Mesopotamia. A number of middle to late Holocene cuneiform tablets make direct reference to rivers. They often record instances in which settlers interacted with the rivers: the digging of new irrigation channels, the annual cleaning of a river or using the river to transport goods from one city to another.

“These texts are useful to determine the locations and period of existence of rivers, particularly when some texts refer to identified sites,” explains Jaafar.

Using this information, Jaafar has been able to identify and map three main courses of the Tigris, during three different time periods. These are, from oldest to the youngest: the Pleistocene course, the Holocene course and the modern course, as are seen in this week’s Imaggeo on Monday’s image.

Sumerian Cuneiform on a clay tablet. From Shuruppak or Abu Salabikh, Iraq, circa 2,500 BCE. British Museum, London. Credit: Gavin.collins, distributed via Wikimedia Commons.

Sumerian Cuneiform on a clay tablet. From Shuruppak or Abu Salabikh, Iraq, circa 2,500 BCE. British Museum, London. Credit: Gavin.collins, distributed via Wikimedia Commons.

No archaeological sites were found associated with the Pleistocene course, compared to the Holocene course, with which many archaeological sites are associated (dated from ~ 4000BC to 1200 AD).

“We have historical texts that suggest that the Holocene Tigris channel was abandoned and relocated to form the new modern course after 1258 AD, in a process known as avulsion” says Jaffar,  “there is also an indication that human activity might have been a trigger for the avulsion,” he adds.

The historical text indicate that farmers broke the banks of the Holocene aged channel of the river Tigris, digging irrigation canals to water low elevation farms.  The newly excavated channel (or canal) became the main waterway.
Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Mountains, rivers and agriculture

This week’s Imaggeo on Mondays image blends a range of geoscience disciplines. The post, by Irene Marzolff, a researcher at Johann Wolfgang Goethe-Universitaet, explores how the mountains, rivers and soils of the High Atlas in Morocco are intrinsically linked to the agriculture of the region.

High Atlas landscape. Credit: Irene Marzolff (distributed via imaggeo.egu.eu)

High Atlas landscape. Credit: Irene Marzolff (distributed via imaggeo.egu.eu)

The image was taken in the southern slopes of the Western High Atlas, north of the city of Taroudannt. The snow of these mountains, which in April is still prevailing on the highest ranges in the background of the photo, is a significant water resource for the region. The high interannual variability of precipitation and its changing patterns associated to climate change present a serious challenge for natural environment and for the sustainable use of water as a resource in agriculture and tourism, the two major economic sectors in the area.

A characteristic open cover of Argan trees (Argania spinosa) can be seen on the lower mountain slopes in the middle distance of the photo: an endemic species with small, oil-rich fruits resembling olives that yield high-quality oil used in medicine, food and cosmetics. The species is a relic of the Tertiary (66 to 2.8 million years ago) but has been under threat from human exploitation for centuries, by excessive grazing, fire-wood cutting, charcoal making and changes to the groundwater table. The area is part of the UNESCO-MAB Biosphere Reserve “Arganeraie” committed to the preservation and sustainable use of the trees.

The river bed in the foreground is formed by fluvial processes typical for this high-mountain region, with highly variable seasonal discharges controlled both by rainfall and snowmelt. It will in the near future drain into the Sidi Abdellah Reservoir that is currently being constructed near Tamaloukt. This reservoir will add to the 10 already existing water storage lakes in the region of Souss Massa Drâa, which is in urgent need of additional water resources: The Souss Valley to the South of the High Atlas is one of Morocco’s most intensely farmed agricultural regions, with agro-industrial production of bananas, vegetables and citrus fruit. Much of this, including 90% of Morocco’s tomato production, is exported to the European market.

By Irene Marzolff, researcher at the Institut fuer Physische Geographie, Johann Wolfgang Goethe-Universitaet, Frankfurt.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Geosciences Column: When water is scarce, understanding how we can save it is important

Geosciences Column: When water is scarce, understanding how we can save it is important

Supplies of water on Earth are running dry. The rate at which an ever growing population consumes this precious resource is not matched by our Planet’s ability to replenish it. Water scarcity is proving a problem globally, with regions such as California and Brazil facing some of the most severe water shortages on record. Used for drinking, agriculture and industrial processes, water forms an fundamental part of our day to day life, so finding ways in which to preserve this vital resource is important.

The global population now exceeds 7.3 billion people. One of the greatest challenges of the 21st century will be to feed this ever growing population – by 2050 crop production will have to double to meet demand. At the same time, agricultural irrigation currently accounts for approximately 80-90% of global freshwater consumption, while agricultural areas requiring irrigation in the past 50 years having roughly doubled. With both space and freshwater in short supply, innovative solutions and fresh approaches will be need if the increase in crop demand is to be met.

The fields in the image are farmed on seemingly vertical hillsides, terrace their fields nearly to the top of every available mountain, and plough by hand or with a draft animal. Terraces, by Cheng Su, distributed via Imaggeo.

The fields in the image are farmed on seemingly vertical hillsides. Terraced fields are  present nearly to the top of every available mountain, and ploughed by hand or with a draft animal. Terraces, by Cheng Su, distributed via imaggeo.

It might come as a bit of a surprise that current irrigations systems operate at efficiency of 50% or below. Water is wasted as it is transported to the crops as well as whilst it is applied to the plants and is affected, not only by the irrigation system itself, but also meteorological and environmental factors. A recent paper published in the open access, EGU Journal, Hydrology and Earth System Sciences, has found that improving current irrigation practices can contribute to sustainable food security.

To better understand where efficiencies might be made in irrigation systems, the scientists used a new approach: They took into account ‘manageable’ factors such as water lost through evaporation, run-off, deep percolation and that taken on by weeds. At the same time, assessing mechanical performance of the systems and the vegetation dynamics, climate, soils and land use properties of a particular region. These factors were fed into a global irrigation model implemented on the three main irrigation types: surface, sprinkler and drip.

The researchers created maps of the global distribution of irrigation systems at a country level, based on the results from their model. The maps showed that areas where surface irrigation – were water is distributed over the surface of a field – is common, irrigation system efficiency was low, sometimes registering values of less than 30%! This is particularly applicable to Central, south and Southeast Asia due to the widespread cultivation of rice. In contrast, areas where there is a high usage of sprinkler systems – similar to natural rainfall – and drip systems (were water is allowed to drip slowly to the root of the plant), such as North America, Brazil, South Africa, Ivory Coast and Europe, efficiency was above the global average.

Global patterns of beneficial irrigation efficiency (Eb, ratio of transpired and diverted water) for each irrigation system – (a) surface, (b) sprinkler, and (c) drip, calculated as area-weighted mean over CFTs (excl. “others” and pastures). This figure is based on theoretical scenarios, in which each system is respectively assumed to be applied on the entire irrigated area.

Global patterns of beneficial irrigation efficiency for each irrigation system (a) surface, (b) sprinkler, and (c) drip. This figure is based on theoretical scenarios, in which each system is respectively assumed to be applied on the entire irrigated area. From Jägermeyr et al., 2015. Click to enlarge.

To investigate how the three irrigation system types compared to one another, irrespective of their geographical distribution, the researchers produced another map. They found that surface irrigation is the least efficient of the three methods, with values at less than 29%. Sprinkler and drip systems perform significantly better, with values of 51 and 70%, respectively. Interestingly, regardless of the system used, irrigation efficiency in Pakistan, northeast India and Bangladesh is always at below global average values. Crop type can also play an important role: rice, pules and rapeseed are linked to poor system efficiencies, whilst, maize sugarcane and root crops (such as potatoes) are above average.

Jägermeyr, the study’s lead author, and his team calculated that 2469km³ of water is withdrawn yearly for irrigation purposes – that is close to 5 times the volume of water held in the Canadian/American Lake Erie. Of that, 608 km³ is non-beneficially consumed. In other words, lost through evaporation, interception (by foliage leaves) and during delivery to the plants and represents an area where substantial water savings could be made.

Replacing surface irrigation with a sprinkler or drip system proves one of the best solutions to the problem, with a potential 76% reduction in non-beneficial consumption of water. This would mean that up to 68% less water would be needed for the purposes of irrigating crops.

Therefore, irrigation system improvements could make an important contribution to sustainably increase food production. The water saved would allow for irrigated areas to be expanded and yields increased on farms where production is currently limited by an insufficient water supply.

The upgrade of irrigations systems seems a very attractive solution to the problem, but the researchers warn that its suitability must be assessed on a river basin level. Factors such as crop management, soil type and local climate may affect the suitability of this approach in some geographical areas. The study finds that regions such as the Sahel, Korea and Madagascar, as well as temperate regions in Europe, North America, Brazil and parts of China would benefit the most from irrigation system improvements.

 

By Laura Roberts Artal, EGU Communications Officer.

 

References

Jägermeyr, J., Gerten, D., Heinke, J., Schaphoff, S., Kummu, M., and Lucht, W.: Water savings potentials of irrigation systems: global simulation of processes and linkages, Hydrol. Earth Syst. Sci., 19, 3073-3091, doi:10.5194/hess-19-3073-2015, 2015.

Gleick, P.H., Christian-Smith, j., Cooley, H.: Water-use efficiency and productivity: rethinking the basin approach, Water International, 36, 7, doi: 10.1080/02508060.2011.631873, 2011.

Tilman, D., Blazer, C., Hill, J., Befort, B.L.: Global food demand and the sustainable intensification of agriculture, PNAS 108, (50), 20260-20264, doi:10.1073/pnas.1116437108, 2011.

Imaggeo on Mondays: The place where water runs through rocks

Imaggeo on Mondays: The place where water runs through rocks

Antelope Canyon, located in Arizona, USA, was formed by erosion of the Navajo Sandstone, primarily due to flash flooding and secondarily due to other sub-aerial processes (think of physical weathering processes such as freeze-thaw weathering exfoliation and salt crystallisation). Rainwater runs into the extensive basin above the slot canyon sections, picking up speed and sand as it rushes into the narrow passageways. Over time the passageways are eroded away, making the corridors deeper and smoothing hard edges in such a way as to form characteristic ‘flowing’ shapes in the rock.

The Navajo Sandstone was deposited in an aeolian (wind-blown) environment composed of large sand dunes: imagine a sea of sand, or an erg, as it is known scientifically, not dissimilar to the present Sarah desert landscape. The exact age of the Navajo Sandstone is controversial, with dated ages ranging from Triassic to early Jurassic, spanning a time period between 250 million years ago to approximately 175 million years ago. The difficulty in determining the exact age of the unit lies in its lack of age diagnostic fossils. The Navajo Sandstone is not alone in this quandary, dating is a common problem in aeolian sediments.

“The picture was taken during a three week Southwest USA road trip in summer 2012. One of the highlights was the visit to Antelope slot canyon, which is located on Navajo land east of Page, Arizona. The Navajo name for Upper Antelope Canyon is Tsé bighánílíní, which means the place where water runs through rocks,” explains Frederik Tack, an atmospheric scientist from the Belgian Institute for Space Aeronomy and author of today’s Imaggeo on Monday’s photograph.

The erosive processes which form the canyon are still ongoing. There is an elevated risk of flash floods, meaning the canyon can only be visited as part of guide tours.

“The canyon was actually quite crowded which made taking this picture challenging, especially as I wanted to capture the peace and solitude of the landscape,” describes Tack.

The effort was worth it: Waved rocks of Antelope slot canyon was one of the EGU’s 2015 Photo Contest finalists!

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

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