SILVAQUA PROJECT. Avaliação dos impactes das alterações climáticas sobre os recursos hídricos e a fixação de CO2 por povoamentos florestais de crescimento rápido em Portugal. Primeiros resultados

Congresso Florestal Nacional: A floresta e as gentes - Actas das ComunicaçõesEstudos recentes referem o impacte das alterações climáticas na evapotranspiração e recursos hídricos, em áreas florestais povoadas com espécies de crescimento rápido, em Portugal (Coelho et al., 2000). Na eventualidade de se verificarem os cenários de diminuição da quantidade de precipitação previstos para o sul da Europa (Parry, 2000), torna-se previsível que várias espécies entrem em stress hídrico tal como Eucalyptus globulus (Coelho et al, 2001), provocando alterações no crescimento dos povoamentos, na decomposição da manta morta e no consumo de água. Espera-se ainda um forte impacte na fixação do CO2 atmosférico. O impacte destas alterações nos processos hidrológicos em solos e vertentes, sob povoamentos de crescimento rápido, é ainda pouco conhecido, sendo o seu conhecimento fundamental para a compreensão dos fenómenos hidrológicos e, essencial no planeamento e gestão eficiente destes recursos. O projecto Silvaqua (POCTI/MGS/49210/2002) foi elaborado no âmbito desta temática, e consiste numa abordagem a várias escalas. (i) estudo dos padrões de variação da humidade do solo para uma série de parcelas onde a humidade do solo é registada segundo diversas redes de sondas de TDR; (ii) monitorização intensiva do crescimento das árvores e arbustos, da queda de folhada e da decomposição da manta morta; (iii) estudo dos processos hidrológicos nas vertentes (nomeadamente caracterização do escoamento e da evapotranspiração) com a delimitação de várias parcelas fechadas e a instrumentação de pequenas bacias hidrográficas; A análise dos resultados permitirá estabelecer os mecanismos de interacção entre as alterações climáticas, o crescimento da vegetação, os processos hidrológicos e os recursos hídricos. O impacte ambiental dos cenários climáticos previstos (Parry, 2000) sobre os recursos hídricos, em termos de alterações de intercepção, de padrões de humidade do solo, de hidrologia das vertentes e das bacias e, sobre a fixação do CO2, em termos de crescimento da vegetação e da dinâmica da camada de manta morta, será estabelecido para vários tipos de povoamentos de eucalipto. A área de estudo localiza-se a 15 km-Este de Águeda e insere-se na bacia hidrográfica do Rio Águeda, na Serra do Caramulo. É efectuado anualmente um inventário florestal das duas micro-bacias em estudo. Os dados obtidos no âmbito do projecto serão usados no modelo GLOB-3PG, de maneira a estimar a produtividade dos povoamentos e a resposta em termos hidrológicos, para diversos cenários climáticos alternativos

Spatiotemporal variability of hydrologic soil properties and the implications for overland flow and land management in a peri-urban Mediterranean catchment

Planning of semi-urban developments is often hindered by a lack of knowledge on how changes in landuse affect catchment hydrological response. The temporal and spatial patterns of overland flow source areas and their connectivity in the landscape, particularly in a seasonal climate, remain comparatively poorly understood. This study investigates seasonal variations in factors influencing runoff response to rainfall in a peri-urban catchment in Portugal characterized by a mosaic of landscape units and a humid Mediterranean climate. Variations in surface soil moisture, hydrophobicity and infiltration capacity were measured in six different landscape units (defined by land-use on either sandstone or limestone) in nine monitoring campaigns at key times over a one-year period. Spatiotemporal patterns in overland flow mechanisms were found. Infiltration-excess overland flow was generated in rainfalls during the dry summer season in woodland on both sandstone and limestone and on agricultural soils on limestone due probably in large part to soil hydrophobicity. In wet periods, saturation overland flow occurred on urban and agricultural soils located in valley bottoms and on shallow soils upslope. Topography, water table rise and soil depth determined the location and extent of saturated areas. Overland flow generated in upslope source areas potentially can infiltrate in other landscape units downslope where infiltration capacity exceeds rainfall intensity. Hydrophilic urban and agricultural-sandstone soils were characterized by increased infiltration capacity during dry periods, while forest soils provided potential sinks for overland flow when hydrophilic in the winter wet season. Identifying the spatial and temporal variability of overland flow sources and sinks is an important step in understanding and modeling flow connectivity and catchment hydrologic response. Such information is important for land managers in order to improve urban planning to minimize flood risk

Soil and water degradation processes in burned areas: lessons learned from a nested approach

Forest fires produce a major impact on soil, water and vegetation. Despite the amount of research published on this subject, there are two major problems that hamper the fully understanding of on and off-site impacts of forest fires. They include methodological problems steaming from the uniqueness of burned soil properties, easily erodible, by the fast degradation they undergo over a short period of time immediately after fire and by the meaning of the impacts at different scales. Monitoring attempts to understand processes in burned areas are hindered by limitations of measuring techniques, that prevent the correct quantification of erosion yields and the processes that give rise to peak flows. A further limitation arises from the poor knowledge on how properties and processes at one scale influence degradation processes at larger scales, both on and off site. This paper presents a reflection about the limitations of some of the methods and techniques more frequently used to assess erosion yields and hydrological responses following fires, and their significance at different scales of analysis. It also shows the potential of nested approaches in the acquisition of an improved insight in to the problem and in the identification of the relevant processes at each scale and how they influence degradation processes at larger areas. It is shown that soil and land use patterns, play a crucial role in reducing or enhancing the hydrological and sediment yield and transport processes between scales

Modelling runoff and erosion, and their mitigation, in burned Portuguese forest using the revised Morgan-Morgan-Finney model

The revised Morgan-Morgan-Finney (MMF) model was used as a modelling approach, which has performed reasonably well to estimate soil losses for burned areas in humid Mediterranean forests in Portugal, and NW Spain. Simple model enhancement approaches are applied to recently burned pine and eucalypt forested areas in north-central Portugal and to subsequent post-wildfire rehabilitation treatments. Model enhancement is validated by applying it to another similar burned area to evaluate model calibration robustness and wider applicability. Model modifications involved: (1) focusing on intra-annual changes in parameters to incorporate seasonal differences in runoff and erosion; and (2) inclusion of soil water repellency in runoff predictions. The main results were that following wildfire and mulching in the plantations: (1) the revised model was able to predict first-year post-fire plot-scale runoff and erosion rates (NS(Runoff)=0.54 and NS(Erosion)=0.55) for both forest types, and (2) first year predictions were improved both by the seasonal changes in the model parameters (NS(Runoff)=0.70 and NS(Erosion)=0.83); and by considering the effect of soil water repellency on the runoff (NS(Runoff)=0.81 and NS(Erosion)=0.89), (3) the individual seasonal predictions were considered accurate (NS(Runoff)=0.53 and NS(Erosion)=0.71), and the inclusion of the soil water repellency in the model also improved the model at this base (NS(Runoff)=0.72 and NS(Erosion)=0.74). The revised MMF model proved capable of providing a simple set of criteria for management decisions about runoff and erosion mitigation measures in burned areas. The erosion predictions at the validation sites attested both to the robustness of the model and of the calibration parameters, suggesting a potential wider application

Interception in pine and eucalypt forest in central Portugal

The LISEM soil erosion model has been applied and tested for small experimental catchments located on the west flank of the Serra do Caramulo in central Portugal within EU funded CLIMED projec

Spatiotemporal variability of hydrologic soil properties and the implications for overland flow and land management in a peri-urban Mediterranean catchment

Planning of semi-urban developments is often hindered by a lack of knowledge on how changes in land-use affect catchment hydrological response. The temporal and spatial patterns of overland flow source areas and their connectivity in the landscape, particularly in a seasonal climate, remain comparatively poorly understood. This study investigates seasonal variations in factors influencing runoff response to rainfall in a peri-urban catchment in Portugal characterized by a mosaic of landscape units and a humid Mediterranean climate. Variations in surface soil moisture, hydrophobicity and infiltration capacity were measured in six different landscape units (defined by land-use on either sandstone or limestone) in nine monitoring campaigns at key times over a one-year period. Spatiotemporal patterns in overland flow mechanisms were found. Infiltration-excess overland flow was generated in rainfalls during the dry summer season in woodland on both sandstone and limestone and on agricultural soils on limestone due probably in large part to soil hydrophobicity. In wet periods, saturation overland flow occurred on urban and agricultural soils located in valley bottoms and on shallow soils upslope. Topography, water table rise and soil depth determined the location and extent of saturated areas. Overland flow generated in upslope source areas potentially can infiltrate in other landscape units downslope where infiltration capacity exceeds rainfall intensity. Hydrophilic urban and agricultural-sandstone soils were characterized by increased infiltration capacity during dry periods, while forest soils provided potential sinks for overland flow when hydrophilic in the winter wet season. Identifying the spatial and temporal variability of overland flow sources and sinks is an important step in understanding and modeling flow connectivity and catchment hydrologic response. Such information is important for land managers in order to improve urban planning to minimize flood risk

Influence of burning intensity on water repellency and hydrological processes at forest and shrub sites in Portugal

In addition to the incineration of vegetation and litter layer, fires are also responsible for the formation of a water repellent layer with significantly different severity and spatial distribution patterns following different burning intensities. Those spatial distribution patterns have an enormous influence on soil wetting patterns, and on hydrological processes at different scales. This study attempts to understand the role of water repellence severity and spatial distribution patterns on soil, slope, and catchment water processes, and on the transmission of hydrological processes between different scales. The comparison between microplot (0.24 m2), plot (16 m2), and catchment

Addressing input data uncertainties in the hydrological simulation of a small forested catchment in North-Central Portugal

The Soil and Water Assessment Tool (SWAT) was employed to carry out a calibration and sensitivity analysis for a small forested catchment in North-Central Portugal. A regional data set allowed obtaining good results with SWAT at the monthly scale but only acceptable model results for daily time steps. The Nash-Sutcliffe model efficiency (E NS) for the validation runoff data was 0.82 and 0.49, respectively. Sensitivity analysis was carried for a total of 20 SWAT parameters. It highlighted the possible importance of groundwater and/or lateral flow in the SWAT results obtained by manual and auto-calibration