Rainfall patterns of Algerian steppes and the impacts on natural vegetation in the 20th century

Abstract

Since 1960, the steppe regions of North Africa have been subject to an increasing desertification, including the degradation of traditional pastures. The initially dominant species (Artemisia herba-alba, Lygeum spartum and Stipa tenacissima) declined and were progressively replaced by other species (Atractylis serratuloides and Salsola vermiculata) that are more tolerant to the new conditions. It is not clear whether these changes are due to anthropogenic reasons or climatic determinism. We have carried out a statistical analysis of the climate to detect putative rainfall changes during the 20 th century in the Algerian steppes based on data from 9 meteorological stations, including 2 Saharan stations (El Oued and Touggourt), 3 pre-Saharan stations (Biskra, Laghouat and Ain Sefra) and 4 steppe stations (Djelfa, Saida, Méchéria and El-Bayadh) located in the arid high plains, which represent the bioclimate diversities of the region. Previous studies suggested that significant rainfall changes for the 20 th century only had records in the south of the Oran region. Most of the studies, however, looked at restricted territories over limited periods, and did not integrate the rainiest period 2004-2014. Our work is designed to integrate all the longest time series of meteorological data available for the steppe regions of Algeria. Our results confirm the spatial rainfall distribution (significant rainfall changes only recorded in the southwestern region) evidenced by previous studies, and reveal a decreasing rainfall gradient from northeastern to southwestern Algeria. Moreover, the results reveal a trend of significant decrease of rainfall in the southern Oran region, marked by two drought periods in 1980 -1985and 1999-2003 the exception of the southwestern region, rainfall overall has not declined since the beginning of the 20 th century. While less marked in other regions, the drought appear to have affected all territories of the Algerian steppe. Consequently, our study implies that the climate was not a leading influence in the on-going degradation of the vegetation cover of steppe landscapes. Such a vegetation evolution thus appears to be have been determined more by human activities than by climate forcing.

The use of Standardized Precipitation Index values (SPI) and MODIS vegetation indices to assess drought of steppe regions, Algeria

“…Because the source of water supply for this type of land use is the atmospheric precipitation, which has declined due to the occurrence of droughts. The same results have been reported by Hourizi et al, (2017) and Belala et al, (2018) [32][33]. Our results are also agree with the findings of Bouarfa et al, (2022) [34], who reported that the significant changes have occurred between the years 2002-2009 around the Djelfa, El Bayadh, and Ain Sefra regions (in the western part of our study area) due to the spatial-temporal extent of drought on steppe vegetation density and resilience.…”

Satellite Monitoring of Natural Reforestation Efforts in China's Drylands

“…Desertification in arid or semi-arid areas has been an environmental issue in regions as geographically diverse as Northern China, the Sahel, or the southwestern United States. [1][2][3] Desertification is associated with anthropogenic causes, 4 such as overgrazing, [5][6][7] logging, or unsustainable agricultural practices, 2,8 and climate change, 9 specifically shifts in the spatial and temporal patterns of rainfall [10][11][12] and gale days (wind velocity greater than 17 m/s). 13,14 When combined, these effects can lead to rapid vegetation cover loss, and subsequent wind erosion can also cause large dust storms, 15 leading to increased fine particulate air pollution with associated adverse health impacts 16,17 and desert encroachment onto vegetated and inhabited areas.…”

Desertification

“…Despite tree-planting efforts, desertification intensified on the steppes, especially in south-western Algeria, due to the prolonged drought during the 1980s. Rainfall declined in the range from 18% to 27%, and the dry season has increased by two months in the last century (Belala et al 2018). Livestock numbers in the Green Dam regions, mainly sheep, grew exponentially, leading to severe overgrazing, causing trampling and soil compaction, which greatly increased the risk of erosion.…”