Impacts of catchment restoration on water availability and drought resilience in Ethiopia: A meta‐analysis

Abstract

The coupled land degradation-drought impacts have been central challenges to ecosystem functioning and livelihood of farmers in Ethiopia. As a response, catchment restoration initiatives have been implemented since the 1970s. The objective of this article is to analyze the effects of such catchment restoration initiatives on water resources and drought resilience, using metadata from 106 peer-reviewed journal articles comprising 361 paired-catchment case-studies. The study shows exclosures, fanya juu (ditches with embankments along the contour), and soil or stone bunds are the major soil and water conservation (SWC) practices implemented to restore degraded catchments in regions prone to land degradation (with a high value for Fournier's degradation coefficient). Runoff depth was less in the treated catchments (97 ± 29 mm yr -1 ) than in the control catchments (168 ± 77) mm yr -1 (n = 217, p < 0.0001). A paired t-test also shows lower runoff coefficients in the treated (13 ± 10%) catchments than in the control catchments (25 ± 15%) (n = 57, p < 0.0001).The conjunctive use of SWC measures enhanced water infiltration into the vadose and aquifer zones. These measures are effective in reducing unproductive water losses. Moreover, the water level in shallow wells raised from a depth of 18 ± 11 to 2 ± 1 m after catchment management. In the dry season, well-functioning catchments promoted upstream-downstream hydrological linkages. The resulting base flow reduced hydrological, agricultural, and socioeconomic drought effects in the treated catchments. To conclude, catchment restoration practices in degraded landscapes have twin goals: enhancing freshwater availability and building drought resilience.We suggest scientists, donors, and managers to work on spreading restoration efforts to other degraded landscapes to improve water yield in the face of climate variability.

Potential for Improved Hydrological Functioning and Stream Baseflows through Forest Landscape Restoration in the Tropics

“…Similar increases in baseflow have also been observed under various drier, non-tropical conditions (but deep soils), such as in Texas after heavy grazing ceased [133], in montane Ethiopia after implementing soil conservation measures coupled with a judicious use of native trees [134], and in the world's largest afforestation experiment: the Loess Plateau in China [68,135]. For the latter, the increased winter baseflows (during the cold dry season) some 20 years after the widespread introduction of soil conservation measures and vegetation is somewhat puzzling in that the establishment of the shrubs and trees under the prevailing low rainfall has produced a dry layer within the soil that hampers deep percolation and groundwater recharge [136][137][138].…”

“…As much of the tropical world includes seasonally-dry climates [16,157], it is sensible to avoid high tree water use in forestation in such water-limited areas [137,138], also in view of the seemingly more limited opportunities for boosting baseflows through forestation (as opposed to soil and water conservation measures to promote infiltration [134]) compared to wetter areas (Figure 2). Several precautions would help to limit excessive water use by planted vegetation [121,[158][159][160][161][162]: (a) choosing species judiciously (e.g., native, slow-growing or deciduous rather than exotic, fast-growing evergreen trees); (b) maintaining a mosaic of vegetations of different ages and types; (c) avoiding short rotations, overly dense planting, and coppicing; and (d) optimising tree cover in accordance with prevailing rainfall and soil conditions.…”

“…More work is needed to characterise and develop suitable management strategies for diverse tropical settings (including areas that have been heavily disturbed or grazed, have acidic or salt-affected soils, or very low or very high rainfall, etc. ), to restore on-site hydrological functioning with potentially positive impacts on the flow regime of affected rivers and streams [134,165,[166][167][168][169].…”

“…Makarieva et al [79] and Sheil [183] emphasise the potential benefits of increased tree cover, in general, including strategically placed forestations, possibly spanning across borders, to enhance rainfall and water availability downwind through intensified moisture convergence [184,185]. Similarly, promoting the infiltration of rainfall through soil conservation measures in seasonally dry areas can elevate soil moisture during the rainy and immediate postmonsoon periods [134,165,167]. This, in turn, has a favourable impact on air temperatures (reduced) and seasonal precipitation [186][187][188][189].…”

A Meta‐analysis of the effects of ground‐based extraction technologies on fine roots in forest soils

“…Thus, a systematic literature review may fail to deepen our knowledge in such topic and therefore we decided to apply a meta‐analytic approach to investigate the effects of ground‐based harvesting technologies on the presence of fine roots in the soil. Meta‐analysis is a statistical technique that is used to develop a literature review summarising the results of several studies dealing with the same topic quantitatively (Gatica et al, 2022; Ghorbani et al, 2023; Gong et al, 2021; Meaza et al, 2022). The main benefit of using meta‐analysis is that the results from several studies with comparable experimental designs are statistically analysed to produce overall conclusions that would not have been evident from a single trial (Hedges et al, 1999; Lajeunesse, 2011).…”