Spatio Temporal Soil Moisture Dynamics and Runoff under Different Soil Cover Conditions in a Semiarid Representative Basin in Brazil

Abstract

Abstract. Hydrological studies in small basins are essential for investigating the role of distinct processes on water resources conservation and to assess the impact of the natural ecosystems on improving water security especially in semiarid environments. In Brazil, the cooperative hydrological Network REHISA (“REde de HIdrologia do SemiÁrido”) comprises hydrologists from several universities of Brazil, focusing on field measurements, monitoring and modeling activities in well instrumented experimental rural catchments located at different regions and biomes in Semiarid environment. Water scarcity is a common aspect among the catchments, as well as risks of soil and water degradation. The objective of this work is to present assessments of near surface soil moisture spatial-temporal distribution, and to evaluate the impact of soil conservation techniques in reducing runoff, using small-scale experimental plots in a representative catchment of the Pernambuco State, Brazil. The study catchment is located in Alto Ipanema River Basin (AIRB) (with an area of 150 km2), which is located at the semiarid region of the São Francisco River (area of 641 000 km2). Soil and water monitoring was performed in experimental plots with different soil cover conditions (Bare soil plots; Plots with natural cover – Caatinga Biome vegetation; Plots with cactus Palma barriers; and Plots with mulch cover – Dry grass mulch at 4 t ha−1), where probes were installed for high resolution soil moisture assessment. In addition, regular soil moisture monitoring campaigns were conducted at 7 different locations, using a capacitance probe, with arboreal and shrub Caatinga vegetation, pasture and bare soil, predominantly Brachiaria decumbens. Mulch cover runs close to the Caatinga cover, but still with higher runoff generation, and presenting lower soil moisture temporal mean values. Caatinga was highly effective in terms of soil and water conservation at the small basin scale for both the dry and the wet season, resulting in a positive nexus between vegetation and water availability at the region.

Evaluating Mulch Cover with Coir Dust and Cover Crop with Palma Cactus as Soil and Water Conservation Techniques for Semiarid Environments: Laboratory Soil Flume Study under Simulated Rainfall

“…For a long time, soil and water conservation practices have been used to reduce runoff and soil losses, prevent land degradation and to improve the fertility and productivity of agricultural soils. Such subject has been addressed based on detailed hydro-meteorological measurements, monitoring campaigns and modelling activities in well-instrumented experimental rural catchments, such as the ones belonging to the Brazilian Semiarid Hydrological Network, REHISA [5][6][7][8][9]. Such field studies under natural rainfall provide for an excellent opportunity to improve the understanding of the actual impact of distinct agricultural conservation practices on water security and soil protection.…”

“…Arguably, the main advantage of such experiments, namely using laboratory soil flumes, is that they allow systematic replication of a wide range of rainfall and/or terrain conditions (e.g., rainfall spatial and temporal characteristics, surface slope, soil roughness, initial soil moisture content). Mulch cover [6][7][8]10,[12][13][14] and cover crop [5,6,8,9] have been shown to provide a higher hydraulic roughness, retarding the surface flow, increasing water infiltration and reducing surface runoff and soil loss, conferring protection to the soil surface from the direct impact of raindrops, thus reducing soil surface crusting, soil compaction, splash erosion and water evaporation and controlling soil temperature fluctuations.…”

Impacto De Métodos Naturais Para Conservação De Água E Solo No Semiárido Brasileiro

“…Em período chuvoso em 2018, verifica-se a pronunciada resposta da parcela com cobertura natural, com elevados picos de umidade, apresentando também uma desfasagem positiva na recessão, ou seja, um padrão de secamento mais lento que os demais tratamentos, apesar da maior transpiração da vegetação natural neste período. Este comportamento também foi verificado por Montenegro et al (2019), para registros em meados de 2017, no mesmo sítio, estando associado à capacidade de armazenamento de água da cobertura vegetal, e ao fluxo pelo caule. Para o período seco, constata-se o adequado desempenho da cobertura morta na manutenção da umidade do solo, seguida pela técnica de barramento em Palma Forrageira.…”

“…Dentre as alternativas naturais de conservação de água e solo adaptáveis às bacias hidrográficas do semiárido, e com baixo custo, destacam-se a cobertura morta com restos vegetais (Santos et al, 2008;Lopes et al, 2019), e os cordões vegetativos como barramentos vegetais, utilizando por exemplo a Palma Forrageira (Opuntia sp.) (Borges et al, 2014;Montenegro et al, 2019). Esses estudos vêm sendo sistematicamente realizados no Estado de Pernambuco, na Bacia Representativa do Alto Ipanema, como parte das ações experimentais da Rede de Hidrologia do Semiárido (REHISA), e mais recentemente do Consórcio Universitas, este último reunindo universidades públicas de Pernambuco em prol do incremento da segurança hídrica no semiárido de Pernambuco.…”

“…(Varela et al, 2014) e a Palma Forrageira (Opuntia sp.) (Montenegro et al, 2019) são alternativas de plantas que podem ser utilizadas nos cordões vegetativos.…”