Is Climate or Direct Human Influence Responsible for Discharge Decrease in the Tunisian Merguellil Basin?

Abstract

Climate change and direct anthropogenic impact are recognized as two major factors affecting catchment runoff. This study investigated the separate effect of each of these factors for runoff from the important Tunisian Merguellil catchment. For this purpose, more than forty years of hydrological data were used. The methodology was based on hydrological characterization, NDVI index to monitor land use dynamics, and the Budyko approach to specify origin of change. The results show that hydrological change is much more important upstream than downstream. The last three decades display a 40% reduction in runoff. This is associated with the direct influence of humans, who are responsible for about 78% of the variation in flow. It appears that climate change contributes to less than about 22%. The combination of increased cultivated land and decreased annual rainfall is the main reason for reduced catchment runoff. Consequently, these effects threaten the sustainable runoff, water in reservoirs, and future water supply in general. Ultimately, the available runoff remains an important parameter and a key indicator to guide the choices of decision-makers and practitioners in current and future climatic conditions. This contributes to supporting sustainable management of remaining water resources.

Drivers of Long-Term Land-Use Pressure in the Merguellil Wadi, Tunisia, Using DPSIR Approach and Remote Sensing

“…The altitude varies between 200 and 1200 m with an average of about 500 m (Figure 1). The basin is located in a semiarid climate, characterized by a very high spatial-temporal variability of precipitation [26]. Annual rainfall varies between 220 mm downstream and 420 mm in the upstream.…”

“…These include springs, hill reservoirs, and tributaries of Merguellil Wadi (Table 5). This is explained by the variability of the rainfall regime and the increase in temperature during the study period [26] as well as soil erosion that causes siltation of the hill reservoirs and the El Houarreb dam. [40].…”

“…Agricultural activities are characterized by diversification and extension of irrigated land; namely arboriculture and a frequent practice of market gardening especially in the center of the basin. This is due to the overexploitation of groundwater by drilling and pumping [26]. In addition, unregulated livestock grazing on public pastures and woodlands eliminates any possibility of sustainable management.…”

Hydrological Droughts in the Eastern Mediterranean Basin Using Hybrid Trend Analysis Methods

“…Stream ow trend analysis is particularly important in river basins, where shifts in stream ow have comprehensive consequences for water resource management. Cultivated areas and decreased rainfall are the main reasons for decreasing trends in watershed stream ow (Khemiri et al, 2021). Gumus et al (2022) clari ed that understanding stream ow trends is essential for designing dams and hydroelectric power plants and effectively managing ood and drought events.…”