DELIMITING TREE TERRITORY FROM SOIL WATER BALANCE EQUATION: A CASE STUDY

A usual problem linked to the apparent complexity of soil-plant interactions with the climatic forcing (as rainfall) is the need to compute the “active soil depth” (zr), available for water storage. Moreover, zr truncates the bottom depth of the control soil column, where drainage takes place, in the computation framework of a supply-demand-storage approach, in solving the soil water balance (SWB) equation at a site. Since the difficulty to estimate zr can lead to arbitrariness to set an operational value to it, our objective was to derive zr as the integral value of a unique soil layer of homogeneous properties. Our experimental scheme to solve the SWB equation involved a sample of ten young, 5 to 6 years-old, evergreen cork-oak (Quercus suber L.) trees, grown on a sandy loam soil (porosity is s), nearby Évora, Portugal. To achieve that goal, we have assembled several measurements techniques to assess the relevant water mass flux density terms, in the soil-plant-atmosphere continuum, as expressed per unit horizontal ground surface area (Ap), so justified by dimensional analysis. A steady-state IRGA (Li-1600M) apparatus was used to measure a discrete time series on instantaneous maximum diffusive conductance (gs) of sunlit leaf samples from four trees, under saturating light and soil water comfort, during spring season (in 2002). Further, gs was up-scaled to the corresponding daily foliage transpiration rate (Tr), which, in turn, was scaled up to plant root water uptake rate (U), using the derived sunlit leaf area index (Li) as the linear scale factor. In the same time period, the mean soil water variation rate (∆S), as induced by U, has been thermo-gravimetrically determined on collected soil core samples. Both ∆S and Tr was related to the spring season depletion phase of the ASW, lasted for a 30-day long period, the volumetric soil water () residence time (RT), under site conditions. Assumption of water mass conservation for the SWB problem in the rooted soil, as well as for whole-plant water capacitance, implies U matches ∆S, the depth-integrated value of variation, throughout zr domain. Results showed zr can be estimated as a cumulative and directly proportional function of observed Tr and RT, without vertical discretization of the soil column. Model output showed an effective maximum rooting depth (or an equivalent lateral expansion) of 1754 mm (1.75 m), which is interpreted as the mean radius of an ellipsoidal zone of influence, in all directions; it was 1.32 times greater than the mean tree high. The product zr s gives the “effective” soil depth, ca. 0.70 m, in this case study. Extension of the approach can be either determining U for pounded water land use system (e.g., rice cultivation) or estimating the plant density in irrigated orchards, enhancing water management

Efeitos do uso do solo na ecohidrologia de bacias hidrográficas

A ocupação e uso do solo, desempenham um importante papel nos fenómenos das mudanças globais constituindo um importante fator que afeta a integridade dos ecossistemas terrestres e aquáticos. Muitas bacias hidrográficas de regiões Mediterrânicas e semi-áridas, caracterizadas durante séculos por sistemas de produção agrícola em extensivo de sequeiro, nas últimas décadas sofreram uma mudança bastante acelerada nos sistemas de produção agrícola devido à perspetiva de uma agricultura de regadio rentável. Apesar do crescente reconhecimento dos impactos dos sistemas agrícolas intensivos, tem-se assistido a um forte incentivo à produção dirigido à intensificação de diversas culturas. Os sistemas de produção agrícola intensivos são caracterizados por uma elevada densidade de plantas, rega sistemática e colheita mecanizada, com incorporação de grandes quantidades de energia e água à custa dos recursos naturais. Estes sistemas associados a um clima em alteração onde os eventos extremos se estão a tornar mais frequentes e mais intensos, têm impactos ambientais negatives fortes, particularmente na erosão do solo, escoamento para corpos de água, degradação de habitats e exploração e contaminação de recursos aquáticos escassos, bem como na degradação dos ecossistemas aquáticos e perda de biodiversidade. A degradação da água e do solo estão largamente associadas à poluição difusa a qual surge em amplas áreas, tais como campos agrícolas ao longo das bacias hidrográficas sobretudo devido à fertilização irracional, rega e uso de pesticidas. As bacias hidrográficas agroflorestais tendem a estar sujeitas a alterações mais disruptivas do uso da terra, devido a ações forçadoras a que esta está sujeita anualmente. Com efeito, em cada ano, mais terra arável é lavrada para culturas arvenses de sequeiro ou, as culturas são cortadas sazonalmente, gerando assim pousios, culturas em linha, rotação de prados ou pastagens. Estas práticas levam a alterações na infiltração, aumentam a erosão e o potencial de contaminação do escoamento. Como resultado, características do solo como o teor em material orgânica, carbono, textura, capacidade de armazenamento de água e fertilidade química, podem alterar-se dramaticamente e os rios enfrentam elevadas chegadas de sedimentos e fertilizantes (principalmente fosfatos e nitratos) com consequências na permeabilidade do substrato, na qualidade da água e na integridade do biota aquático. Este fenómeno é particularmente agravado em regiões com elevada variabilidade no regime de precipitação, onde as cheias alternadas com períodos de seca, promovem condições que levam ao aumento da erosão do solo e perda de nutrientes, particularmente em bacias hidrográficas com elevadas alterações no uso e ocupação do solo. Assim, o objetivo deste estudo consistiu em avaliar o efeito do uso e ocupação do solo em duas pequenas bacias hidrográficas do Sul de Portugal, relativamente à composição do solo, qualidade da água e integridade do biota aquático, especificamente através da fauna piscícola. Apesar de preliminar, este estudo ilustra a relação entre os usos de solo e a integridade dos recursos naturais associados. O impacto dos agro-sistemas resulta do seu grau de intensificação mas também de múltiplas outras pressões a eles associadas, as quais individualmente ou em conjunto afetam o serviço dos ecossistemas de suporte às atividades humanas e à conservação da biodiversidade. Nesta perspetiva é importante que o ordenamento e gestão das bacias hidrográficas integrem uma visão de compromisso entre os usos de solo associados à intensificação dos sistemas agrícolas e a conservação dos recursos naturais e ecossistemas associados, por forma a promover o desenvolvimento sustentável da agricultura

Climate and Landuse Change Impacts on hydrological processes and soil erosion in a dry Mediterranean agro-forested catchment, southern Portugal

Climate change is expected to increase aridity in the Mediterranean rim of Europe, due to decreasing rainfall and increasing temperatures. This could lead to impacts on soil erosion, since the lower rainfall could nevertheless become concentrated in higher intensity events during the wet season, while the more arid conditions could reduce vegetation cover, also due to climate-induced land-use changes. In consequence, there is an interest in understanding how climate change will affect the interaction between the timing of extreme rainfall events, hydrological processes, vegetation growth, soil cover and soil erosion. To study this issue, the SWAT eco-hydrological model was applied to Guadalupe, an agro-forested catchment (446 ha) located close to the city of Évora, with a Mediterranean inland climate. The landcover is a mix of dispersed cork oak forests (“montado”), annual crops, and agroforesty regions where the cork oaks are associated with crops or pasture; this land cover is representative of the dry regions of southern Portugal and Spain. The catchment has been instrumented since 2011 with a hydrometric station (water discharge and suspended sediment concentration data) and a soil moisture measurement station. There is also observed data of actual evapotranspiration, LAI and biomass production (in pasture; from 1999 and 2008) and runoff data and sediment yield measured in six 16m2 plots. Water balance, vegetation growth, soil erosion and sediment yield in SWAT was calibrated with this dataset. This work will present the dataset, modeling process, results for impacts of climate and land-use change scenarios for vegetation growth, soil erosion and sediment export, considering the climate and socio-economic scenarios A1b and B1 (based on SRES storylines). Climate scenarios were created by statistical downscaling from Global Circulation Models (GCMs) for the period 2071-2100 (30 years). The reference period was 1971-2000 (30 years). The SWAT model was used to estimate long-term erosion rates for the reference period, as well as the role of extreme events, particularly those falling in the late autumn and early winter (when the soil cover is minimal); the model was then used to examine the impacts of changing temporal patterns of low vegetation cover and extreme events for erosion and sediment yield

Impacts of climate change on erosion in humid and dry Mediterranean regions of Portugal

Soils in the Mediterranean regions of Europe are often vulnerable to soil erosion, due to a combination of annual plant cover cycles, centuries of human use, the concentration of rainstorms in a short period of the year, and other factors. Climate change could bring about a warmer and drier climate, limiting vegetation growth while bringing heavier storms during winter. This could eventually lead to higher risks of soil losses and the consequential problems of land degradation and desertification. Project ERLAND, which began in 2009, is assessing these risks for two Mediterranean research catchments in Portugal, with four main goals: (i) collect data to understand hydrological and erosion processes in representative catchments; (ii) use this data to parameterize the SWAT eco-hydrological and erosion model as accurately as possible; (iii) use future socio-economic scenarios to estimate both impacts on climate change and on future land-use practices; and (iv) apply the SWAT model for these scenarios and estimate the consequences for soil erosion rates. The Macieira catchment is in a wet Mediterranean climate region, with high rainfall (c. 1300 mm.y-1) but a distinct summer dry season; erosion processes are associated with periods of sparse cover in autumn in fields with a pasture-corn rotation, but also with forest plantations after clear-cutting and especially after forest fires. The occurrence of a forest fire inside the catchment in 2011 allowed an analysis of the role played by this kind of disturbances on soil erosion. Climate change could bring less erosive rainfall events, but an increase in fire frequency, and therefore a potential shift of erosion from agriculture to forest land-uses. The Guadalupe catchment has a dry Mediterranean climate (rainfall of c. 550 mm.y-1); erosion processes occur mostly in permanent crops (olive trees) and winter cereal fields. Climate change could bring a concentration of rainfall in winter, as well as an increase in the area with permanent crops, bringing additional exposure to erosion. This communication presents the overall concept and work performed in project ERLAND, including an assessment of the large impact of the fire in the wet catchment (Macieira) on soil erosion rates, where results indicate that soil losses after soil preparation for forest replanting might be equivalent, in long-term, to soil losses in agricultural fields. It also provides preliminary results for the impacts of climate change on soil erosion in the dry catchment (Guadalupe), which indicate a potential increase of soil loss rates by 2100 in the most vulnerable areas (winter cereal fields and olive groves) due to a higher concentration of rainfall in winter. The foreseen replacement of some winter cereals and pastures by sunflower cultivation for biofuel production could also lead to important changes in erosion rates

Evaluation of future climate change impacts on semi-arid Cobres basin in southern Portugal

This study evaluated future climate change impacts on hydrological and sediment transport processes for the medium-sized (705 km2) agriculture dominated Cobres basin, Portugal, in the context of anti-desertification strategies. We used the Spatial-Temporal Neyman-Scott Rectangular Pulses (STNSRP) model—RainSim V3, a rainfall conditioned weather generator—ICAAM-WG, developed in this study but based on the modified Climate Research Unit daily weather generator (CRU-WG), and a PBSD hydrological model—SHETRAN, to downscale projections of change. Climate projections were derived from the RCM HadRM3Q0 output, provided by the ENSEMBLES project, for the SRES A1B scenario for the period 2041–2070. The RainSim V3 and ICAAM-WG models are demonstrated to be able to reproduce observed climatology for the period 1981–2010. The SHETRAN model reproduces hourly runoff with Nash-Sutcliffe Efficiency (NSE) of 0.86 for calibration (2004–2006) and 0.74 for validation (2006–2008) for basin outlet; it reproduces hourly sediment discharge with NSE of 0.48 for the storm from October 23rd 2006 to October 27th 2006. We found that future mean climate is drier, with mean annual rainfall decreased by 88 mm (19%), mean annual PET increased 196 mm (16%) and consequent mean annual runoff and sediment yield decreased respectively 48 mm (50%) and 1.06 t/ha/year (45%). The future mean annual AET decreases 41 mm (11%), which occurs mainly in spring indicating a more water-limited future climate for vegetation and crop growth. Under current conditions, November to February is the period in which runoff and sediment yield occur frequently; however, it is reduced to December to January in future, with changes in the occurrence rate of 50%. On the other hand, future wet extremes are more right-skewed. Future annual maximum discharge and sediment discharge decrease for extremes with return periods (T) less than 20 years and the decreases are especially greater for those with T less than 2 years; besides, both quantities present the same or slightly lower magnitudes as those with T larger than 20 years. The annual maximum discharge (sediment discharge) series, under control climate, follows the GEV distribution with location parameter of 64.6 m3/s (164.4 kg/s), scale parameter of 46.5 m3/s (120.3 kg/s) and shape parameter of 0.09 (-0.24); under future climate, the annual maximum discharge series follows the gamma distribution with scale parameter of 75.2 m3/s and shape parameter of 0.97 and the annual maximum sediment discharge series follows the three-parameter lognormal distribution with location parameter of -46.2 kg/s, mean of 5.3 kg/s and standard deviation of 0.78. This study has confirmed the increasing concerns of water scarcity and drought problems in southern Portugal; but it also indicated the mitigation of sediment transport for most of time in the future except heavy events. However, the results should be interpreted carefully since we did not consider possible changes of land-use in the future, as well as the climate and hydrological modelling uncertainties

ESTIMATING THE IMPACTS OF CLIMATE CHANGE ON SOIL EROSION IN MEDITERRANEAN WATERSHEDS

Climate change could impact soil erosion in Mediterranean regions, through both higher climatic aridity - leading to less vegetation cover - and higher winter rainfall intensity. This could have the effect of increasing soil degradation and accelarating ongoing desertification processes. Project ERLAND aims to study the potential impacts of climate changes on vegetation growth, hydrology and erosion in Portuguese watersheds, and define the costs and benefits of different adaptation options. This will be achieved by building an ecohydrological and erosion model to two well instrumented watersheds, in order to ensure an appropriate simulation of the most important processes which could be affected by climate change. This presentation will illustrate the project's objectives and ongoing work on two representative agroforestry cathments with typical land cover/use conditions. The Macieira de Alcoba catchment in northern Portugal has a humid climate, and is covered with commercial eucalypt/pine forests interspersed with agricultural fields, where summer cereals and pastures are associated with vineyards. The Guadalupe catchment in southern Portugal has a dry climate and is covered with extensive cork oak forests (of a Portuguese "montado" land-use-system) associated with winter cereals and pastures. On each catchment, runoff and sediments are being collected simultaneously at the field (two open plots) and catchment (one hydrometric station) scales, together with other data such as meteorology, soil moisture, and some vegetation growth parameters. The field sites will be maintained at the present level during two years, and the hydrometric stations will be left for a larger period afterwards in order to collect the largest possible data series. The presentation will focus on the ongoing data collection on the two study sites and how the data will be used to fullfil the project's goals, i.e. the evaluation of an ecohydrological and erosion model for use in climate change studies

Processes influencing ozone levels in Alaskan forest fire plumes during long-range transport over the North Atlantic

A case of long-range transport of a biomass burning plume from Alaska to Europe is analyzed using a Lagrangian approach. This plume was sampled several times in the free troposphere over North America, the North Atlantic and Europe by three different aircraft during the IGAC Lagrangian 2K4 experiment which was part of the ICARTT/ITOP measurement intensive in summer 2004. Measurements in the plume showed enhanced values of CO, VOCs and NOy , mainly in form of PAN. Observed O3 levels increased by 17 ppbv over 5 days. A photochemical trajectory model, CiTTyCAT, was used to examine processes responsible for the chemical evolution of the plume. The model was initialized with upwind data and compared with downwind measurements. The influence of high aerosol loading on photolysis rates in the plume was investigated using in situ aerosol measurements in the plume and lidar retrievals of optical depth as input into a photolysis code (Fast-J), run in the model. Significant impacts on photochemistry are found with a decrease of 18% in O3 production and 24% in O3 destruction over 5 days when including aerosols. The plume is found to be chemically active with large O3 increases attributed primarily to PAN decomposition during descent of the plume toward Europe. The predicted O3 changes are very dependent on temperature changes during transport and also on water vapor levels in the lower troposphere which can lead to O3 destruction. Simulation of mixing/dilution was necessary to reproduce observed pollutant levels in the plume. Mixing was simulated using background concentrations from measurements in air masses in close proximity to the plume, and mixing timescales (averaging 6.25 days) were derived from CO changes. Observed and simulated O3/CO correlations in the plume were also compared in order to evaluate the photochemistry in the model. Observed slopes change from negative to positive over 5 days. This change, which can be attributed largely to photochemistry, is well reproduced by multiple model runs even if slope values are slightly underestimated suggesting a small underestimation in modeled photochemical O3 production. The possible impact of this biomass burning plume on O3 levels in the European boundary layer was also examined by running the model for a further 5 days and comparing with data collected at surface sites, such as Jungfraujoch, which showed small O3 increases and elevated CO levels. The model predicts significant changes in O3 over the entire 10 day period due to photochemistry but the signal is largely lost because of the effects of dilution. However, measurements in several other BB plumes over Europe show that O3 impact of Alaskan fires can be potentially significant over Europe

Impacts of climate and land use changes on the hydrological and erosive response of a humid and dry Mediterranean catchment

The impacts of climate and land use changes on streamflow and sediment export were evaluated for a humid (São Lourenço) and a dry (Guadalupe) Mediterranean catchment, using the Soil and Water Assessment Tool (SWAT) model. SWAT was able to produce viable streamflow and sediment export simulations for both catchments, which provided a baseline for investigating climate and land use changes under the A1B and B1 emission scenarios for the period between 2071 and 2100. Compared to the baseline period (1971-2000), climate change scenarios forecasted a decrease in annual precipitation in both catchments (humid, both scenarios: -12%; dry, both scenarios: -8%), but with strong increases during winter. Land use changes followed a socio-economic storyline in which traditional agriculture was replaced by more profitable land uses, i.e. corn and commercial forestry at the humid site and sunflower at the dry site. Climate changes led to a decrease of streamflow in both catchments (humid, both scenarios: -13%; dry, A1B: -14%; B1: -18%), mostly as a consequence of the projected decrease in rainfall. Land use changes led to small increases in flow discharge, but a higher increase was observed for the dry site under scenario A1B (humid, A1B: +0.3%; B1: +1%; dry, A1B: +6%; B1: +0.3%). The combination of climate and land use scenarios was mostly dominated by the climatic response, since a decrease in streamflow was observed for both catchments (humid, A1B: -13%; B1: -12%; dry, A1B: -8%; B1: -18%). Regarding the erosive response, clear differences were observed between catchments mostly due to differences in both the present-day and forecasted vegetation types. Climate scenarios led to a decrease in sediment export at the humid catchment (A1B: -11%; B1: -9%) and to an increase at the dry catchment (A1B: +24%; B1: +22%) in the first case due to the predominant vegetation type (vineyards and maritime pine) providing year-round cover, while in the second, due to annual crops (wheat and pasture) exposing soils during winter. For land use scenarios, the same contrast occurred between catchments (humid, A1B: -18%; B1: -10%; dry, A1B: +257%; B1: +9%) due to the expansion of permanent cover vegetation in one case and annual crops in the other. Climate and land use changes had off-setting effects on sediment export at the humid catchment (A1B: -29%; B1: -22%), as a result of reduced precipitation and cultivation of more soil-protective crops. A different response was observed for the dry catchment (A1B: +222%; B1: +5%), as the increase in sediment export associated with the cultivation of highly erosion-prone crops was not aggravated by the higher rainfall amounts forecasted for winter months. The results of the present study highlight that indirect impacts of climate change, like land use changes, might be similar or more severe than direct impacts

Análise entre a Declividade e a Ocorrência de Escorregamentos de Terras na Bacia dos Rios Pedras/Pituaçu em Salvador/Ba

Os prejuízos associados aos desastres naturais vêm aumentando a cada ano no Brasil, principalmente devido ao denso crescimento populacional, uma vez que a população urbana representa mais de 84% da população do país, e com tendência de crescimento nas próximas décadas (BRITO et al., 2016), e ao mau planejamento urbano. A variável declividade do terreno é um dos principais condicionantes à ocorrência de escorregamentos de terras (BORTOLUCCI, 2015), sendo, dessa forma, uma variável muito utilizada em estudos que envolvem esta temática ambiental. A cidade de Salvador apresenta áreas com encostas íngremes e baixadas, e por este motivo a variável declividade da Bacia Hidrográfica dos Rios Pedras/Pituaçu, localizada nesta cidade, será aqui relacionada com a ocorrência de escorregamentos de terras lá verificados, e com isso possibilitar uma ferramenta de auxílio aos órgãos tomadores de decisões e, assim, IMPACTOS, RISCOS E DESASTRES NATURAIS consequentemente mitigar os impactos negativos à sociedade em geral diante dos episódios de precipitação que anualmente atingem Salvador