Susceptibilidade à Erosão Hídrica na Bacia da Ribeira Seca (Santiago, Cabo Verde)

Na Ilha de Santiago, em Cabo Verde, a erosão hídrica é o processo que afecta áreas mais extensas. A ocorrência de aguaceiros intensos e concentrados no tempo e no espaço promovem uma marcada erosividade das precipitações, com forte irregularidade regional. A grande variabilidade dos declives e das formas das vertentes, associadas à diversidade litológica, bem como à multiplicidade de ocupação do solo, permitem condições de erodibilidade muito contrastadas no espaço. O objectivo deste trabalho é obter um mapa de susceptibilidade à erosão hídrica para a bacia da Ribeira Seca (Santiago oriental) com base no modelo digital do terreno (MDT), nos mapas geológico e de ocupação do solo e na distribuição da erosividade das precipitações. Verifica-se que o sector sudeste da bacia é o mais susceptível à erosão hídrica, pois nele ocorrem a maior concentração diária das precipitações e as condições geomorfológicas e de coberto do solo de mais elevada erodibilidade.

Evaluation of Remediation Recommendations: Stakeholder Workshop 3 Ribeira Seca - Cape Verde

In Cape Verde, the low soil cover and inadequate practices on rain fed agricultural lands constitute major problems related to desertification. To the fragility of the land associates severe water erosion, causing tons of land to be washed away from the fields every year during the rainy season. Therefore, the aim in the scope of combating desertification is to provide a certain degree of permanent soil cover to serve as shield for the impact of rain. During the selection workshop several technologies, all related to vegetative cover either as strips or surface cover were discussed. Only two technologies were selected: vegetation strip with pigeon pea and afforestation with fruit trees.  Technology 1: Pigeon pea (cajanus cajan) barriers/strips. It consists in planting seeds of pigeon pea, a leguminous perennial shrub that has dual purpose of protecting the soil and feed people. It is planted in association with maize crop. After the maize is harvested, the soil remains with some degree of cover. Though the objective was to plant as strip barriers, six meters apart, most farmers planted it as surface cover.  Technology 2: Afforestation with fruit trees. It consists in the plantation of different fruit tree species in humid areas to provide both soil cover and feed for farmers. Since fruit trees require several years to provide effective cover, and though it was implemented in some areas, it was not evaluated during the project’s period.

Evaluation of Remediation Recommendations: Stakeholder Workshop 3 Ribeira Seca - Cape Verde

In Cape Verde, the low soil cover and inadequate practices on rain fed agricultural lands constitute major problems related to desertification. To the fragility of the land associates severe water erosion, causing tons of land to be washed away from the fields every year during the rainy season. Therefore, the aim in the scope of combating desertification is to provide a certain degree of permanent soil cover to serve as shield for the impact of rain. During the selection workshop several technologies, all related to vegetative cover either as strips or surface cover were discussed. Only two technologies were selected: vegetation strip with pigeon pea and afforestation with fruit trees.  Technology 1: Pigeon pea (cajanus cajan) barriers/strips. It consists in planting seeds of pigeon pea, a leguminous perennial shrub that has dual purpose of protecting the soil and feed people. It is planted in association with maize crop. After the maize is harvested, the soil remains with some degree of cover. Though the objective was to plant as strip barriers, six meters apart, most farmers planted it as surface cover.  Technology 2: Afforestation with fruit trees. It consists in the plantation of different fruit tree species in humid areas to provide both soil cover and feed for farmers. Since fruit trees require several years to provide effective cover, and though it was implemented in some areas, it was not evaluated during the project’s period.

Improving rainwater-use in Cabo Verde drylands by reducing runoff

Dryland agriculture in Cabo Verde copes with steep slopes, inadequate practices, irregular intense rain, recurrent droughts, high runoff rates, severe soil erosion and declining fertility, leading to the inefficient use of rainwater. Maize and beans occupy N80% of the arable land in low-input, low-yielding subsistence farming. Three collaborative field trialswere conducted in different agroecological zones to evaluate the effects ofwater-conservation techniques (mulching of crop residue, a soil surfactant and pigeon-pea hedges) combinedwith organic amendments (compost and animal or green manure) on runoff and soil loss. During the 2011 and 2012 rainy seasons, three treatments and one control (traditional practice) were applied to 44- and 24-m2 field plots. A local maize variety and two types of beanswere planted. Runoff and suspended sedimentswere collected and quantified after each daily erosive rainfall. Runoff occurred for rainfalls≥50mm(slope b10%, loamy Kastanozem),≥60mm(slope≤23%, silt–clay–loam Regosol) and≥40mm(slope≤37%, sandy loam Cambisol). Runoffwas significantly reduced only with themulch treatment on the slope N10% and in the treatment of surfactant with organic amendment on the slope b10%. Soil loss reached 16.6, 5.1, 6.6 and 0.4 Mg ha−1 on the Regosol (≤23% slope) for the control, surfactant, pigeon-pea and mulch/pigeon-pea (with organic amendment) treatments, respectively; 3.2, 0.9, 1.3 and 0.1 Mg ha−1 on the Cambisol (≤37% slope) and b0. 2Mg ha−1 for all treatments and control on the Kastanozem(b10% slope). Erosion was highly positively correlated with runoff. Mulch with pigeon-pea combinedwith an organic amendment significantly reduced runoff and erosion fromagricultural fields on steep slopes, contributing to improved use of rainwater at the plot level. Sustainable land management techniques, such as mulching with pigeon-pea hedges and an organic amendment, should be advocated and promoted for the semiarid hillsides of Cabo Verde prone to erosion to increase rainwater-use and to prevent further soil degradation.

Appraising and selecting strategies to combat and mitigate desertification based on stakeholder knowledge and globalbest practices in Cape Verde Archipelago

Cape Verde is considered part of Sahelian Africa, where drought and desertification are common occurrences. The main activity of the rural population is rain-fed agriculture, which over time has been increasingly challenged by high temporal and spatial rainfall variability, lack of inputs, limited land area, fragmentation of land, steep slopes, pests, lack of mechanization and loss of top soil by water erosion. Human activities, largely through poor farming practices and deforestation (Gomez, 1989) have accelerated natural erosion processes, shifting the balance between soil erosion and soil formation (Norton, 1987). According to previous studies, vegetation cover is one of the most important factors in controlling soil loss (Cyr et al., 1995; Hupy, 2004; Zhang et al., 2004; Zhou et al., 2006). For this reason, reforestation is a touchstone of the Cape Verdean policy to combat desertification. After Independence in 1975, the Cape Verde government had pressing and closely entangled environmental and socio-economic issues to address, as long-term desertification had resulted in a lack of soil cover, severe soil erosion and a scarcity of water resources and fuel wood. Across the archipelago, desertification was resulting from a variety of processes including poor farming practices, soil erosion by water and wind, soil and water salinity in coastal areas due to over pumping and seawater intrusion, drought and unplanned urbanization (DGA-MAAP, 2004). All these issues directly affected socio-economic vulnerability in rural areas, where about 70% of people depended directly or indirectly on agriculture in 1975. By becoming part of the Inter- State Committee for the Fight against Drought in the Sahel in 1975, the government of Cape Verde gained structured support to address these issues more efficiently. Presentday policies and strategies were defined on the basis of rational use of resources and human efforts and were incorporated into three subsequent national plans: the National Action Plan for Development (NDP) (1982–1986), the NDP (1986–1990) and the NDP (1991–1995) (Carvalho

As Barragens em cabo Verde - Avaliação dos Impactes Ambientais - Socioeconómicos e Culturais - Caso de Estudo - A Barragem do Poilão Ilha Santiago

Os sucessivos anos de seca têm agravado a crónica falta de água que marca o quadro hídrico de Cabo Verde. No arquipélago verifica-se a perda de um grande volume de água que se escoa para o mar, aquando das grandes chuvadas, e que é estimado em milhões de m3/ano. Para atenuar a problemática da falta de água, principalmente no setor agrícola, o Governo Cabo-verdiano tem apostado na política de construção de barragens. No ano de 2006 com o objetivo de aumentar os recursos hídricos disponíveis e concomitantemente alargar a área irrigada e diminuir a pobreza, foi inaugurada a barragem do Poilão, a primeira do arquipélago, no interior da ilha de Santiago no concelho de São Lourenço dos Órgãos. Baseado no pressuposto que as barragens são estruturas de grande impacte ambiental e socioeconómico, antes, durante e depois da sua construção, o presente trabalho tem como objetivo principal avaliar o desempenho ambiental, socioeconómico e cultural da Barragem de Poilão. Para tal, o trabalho segue uma metodologia DPSIR1e a aplicação de inquéritos e entrevistas, procurando integrar o conhecimento e a perceção da paisagem na área de influência da albufeira por parte de diversos atores locais. Espera-se colher subsídios que sirvam de base para os estudos futuros das demais barragens projetadas e a serem construídas em Cabo Verde.