Bernhard Lucke

Questioning Transjordan’s Historic Desertification: A Critical Review of the Paradigm of ‘Empty Lands’

Abstract European travel reports of the 19th century and excavations in Transjordan created the impression that population numbers were strongly reduced during the Islamic periods, leading to ‘empty’ lands which were only resettled during the early 20th century. This development was considered to be caused by bad (Muslim) governance, nomadic incursions, and environmental degradation. However, our case study near the ancient site Abila of the Decapolis in northern Jordan found that the land was never empty and always fertile, but there is evidence for a rapid and intense landscape change during the Late Byzantine period. This was probably caused by a significant shift to aridity which also triggered socio-economic changes in subsistence strategies from agriculture to nomadism. The climatic change seems to have occurred rapidly within approximately 100 years in the late 6th and early 7th centuries AD and was accompanied by heavy rainfall events. It might have been caused or triggered by the climatic event of the ‘Mystery Veil’ which the Byzantine historian Procopius described in the year 536 AD. During the Medieval period, settlement density increased again until another decline took place in the late Ottoman period. However, the vicinity of Abila was probably never abandoned and the continuity of place names speaks against a larger exchange of population. Rising population numbers and favourable climatic conditions in the early 20th century caused most tribes to settle again, which improved government control.

Sustainability in the Desert

According to the definition of sustainability, the achievements of past civilizations, e.g. the floodwater farming near the site of Umm el-Jimal, were sustainable since they did not rely on non-renewable resources. But they did not allow continuous settlement from antiquity until today. It is often assumed that breaks in settlement history were due to over-exploitation of the environment, e.g. overgrazing and soil erosion [1].

The Past as a Key for the Future: Mutual Dependencies of Land Use, Soil Development, Climate and Settlement

It is of high actual importance to clarify historic climate variations and their impact, because it is not possible to predict future developments and their drivers, unless those of the past are understood. The Decapolis area in northern Jordan provides excellent opportunities to analyze this question. Environmental change as a result either or of human activities or of climate variation could have been responsible for the abandonment of the area by Arab farmers in medieval times. Recent studies let the climatic changes are the more likely reason. There are several arguments for this conclusion: Climatic models match very well to the historical development. The Arab farmers were also highly skilled. Our investigations revealed a very heterogeneous land use and soil development pattern, and found no evidence for a sudden, widespread general erosion event. In contrast, relic surfaces and the soil’s genesis point to moister conditions in the past and differences in the soil’s development point to diverse land use intensities. Though it is evident that land use changed the character of the landscape and can be tracked according to soil development, it did not lead to advancement of the desert. It therefore seems that desertification is related to climate change.

Assessing the spatial variability of soil surface colors in northern Jordan using satellite data from Landsat-8 and Sentinel-2

ABSTRACT In the semi-arid regions of northern Jordan, soil surface colors show gradual variation from west to east. The dominant soil color in the northwest is a dark reddish brown. Toward the east, lighter brown colors dominate, and colors change further to light yellow in the east. These changes coincide with a climatic gradient (mean annual precipitation). Earlier studies showed a close and possibly causal correlation of soil colors (redness), soil weathering intensity, and mean annual precipitation. However, these conclusions were based on a limited number of soil samples. Our study, in contrast, shows the regional variability of soil colors in the context of geomorphological conditions and the climatic gradient. Two thematic maps of soils surface colors depending on verified supervised classification of Landsat-8 and Sentinel-2 data were created. Results show a remarkable similarity of Support Vector Machines (SVM) classification of Landsat-8 and Sentinel-2 in the area, and confirm a strong correlation of red soil color distribution, mean annual precipitation, and geomorphological aspects (depressions leading to higher water availability and thus soil weathering intensity). Accordingly, this approach offers suitable tools for a quantitative investigation of soil color distribution under the consideration of climatic gradients and varying geomorphological conditions.

Soils in Arid and Semiarid Regions: The Past as Key for the Future

Growing populations, increasing food demand, and technological advances may soon lead to intensifying land use in semiarid and arid countries through the spread of irrigated agriculture. Improved water harvesting and desalinization technology, coupled with higher efficiency of regenerative energies, might allow to widely extend irrigated areas. While this is a positive development in the light of growing demands for water and food, it presents challenges for land-use planners. Negative examples like Lake Aral make clear that a careful analysis is required before embarking on large-scale irrigation projects.

The Potential of Progressive Development

The overview of developments in the desert makes clear that Progressive Development is already implemented is many areas, although it is not acknowledged as such and a coordinating master plan is missing. International plans would be very desirable, since water is a transboundary issue. For example, exploitation of the Disi aquifer led to conflict between Jordan and Saudi Arabia [1]. Jordan, Syria, Israel and Palestine share the Yarmouk River as the primary freshwater resource, which is a very sensitive political issue.

Some Examples of Development in the Desert Belts

Most semi-arid regions face strong population growth. For example, with the actual growth rate in Jordan, population doubles every 25 years. Many countries in the desert belt experienced rapid modernisation during the last 50 years. Taking Jordan again as an example, modern western life styles are spreading quickly. They co-exist with traditional herding and farming in the rural areas, but urbanization is rapidly expanding.

The Socio-Economic Framework: What Can be Learned from Earlier Failures?

Large-scale irrigation projects are theoretically beneficial; however there are examples of outstanding failures which partly led to ecological catastrophes. We think that irrigation per se does not necessarily lead to land degradation. Even in the famous case of the Mesopotamian plains, the idea that ancient Sumerian irrigation caused irreversible salinization [1] is far less evident than often assumed in the public discussion [2].

The Feasibility of Progressive Development

It is a deeply entrenched belief that historic land use led to land degradation in the desert belts. Supposedly, overgrazing and farming caused erosion, and irrigation led to salinization. Considering the gaps in settlement history, mismanagement is considered a prime reason for abandonment [1–3]. If this is so, Progressive Development might be doomed to fail, because the soils are already degraded and will inevitably degrade further. Climate variations, however, can also lead to degradation, and might have caused the fluctuations of settlement history. The correct assessment of the past will be most important for evaluating the impact of Progressive Development. This and the geographic law of soil zonality allow predicting how soils and the environment will develop under irrigation and permanent vegetation.