PL6

Desertification processes affect ground surface properties and soil-water availability, thus impacting vegetation dynamics and ecosystem functioning. Semiarid areas – encompassing the major part of grazing lands and providing a wide range of ecosystem services – are subjected to both ‘natural’ and anthropogenic degradation processes. Afforestation has been widely accepted as an effective means of halting land degradation and adapting to climate change. However, recent studies have shown that dryland afforestation might adversely affect geo-ecosystem functioning.

Across the Israeli drylands, afforestation projects have been implemented by the Keren Kayemet Le’Israel (KKL) to restore degraded lands. These projects rely on harvesting water overland flow and are designed to accumulate runon water, sediments, and nutrients from runoff contributing source areas. Such systems have been established both in hillslopes and valleys, allowing the support of woody vegetation, such as trees and shrubs.    The most common runoff harvesting systems in the northern Negev region are contour bench terraces (in hillslopes) and limans (in valleys). In the hillslope-afforestation systems, the woody canopy coverage area varies from 0.1% in the youngest planting areas to ~1.0% in the eldest areas.

In this study, we analyzed the temporal development of different planted sites in the Ambassador’s afforestation land. The area has been under afforestation since 2005. For this study, we selected four sites within the afforestation area, including (1) undisturbed, control hillslopes, where no water harvesting systems nor tree planting have been conducted; (2) hillslopes that were planted just before the hydrological year of 2005; (3) hillslopes that were planted just before the hydrological year of 2009; and (4) hillslope that were planted just before the hydrological year of 2016.

Long-term analysis of meteorological trends revealed that the area had been subjected to substantial climatic change. A decadal rate increase of 0.45°C was observed in air temperature, while a 1.3% decrease in (minimal) relative humidity. Although a long-term change in evapotranspiration has not been detected, summer values have been significantly increased.

For each of the afforestation sites (2005, 2009, and 2016), a significant reduction in seasonal Normalized Difference Vegetation Index (NDVI) values were recorded compared to the undisturbed slopes, a trend that took place until the establishment of runoff harvesting systems. However, in the 2005 and 2009 sites, the NDVI seasonal average was significantly higher after the establishment of runoff harvesting systems than that in the prior seasonal values, as well higher than that in the undisturbed hillslopes. At the same time, in the newly disturbed sites planted in 2016, the average seasonal values were substantially lower after the establishment of runoff harvesting systems than those in the prior year.

How to cite: Argaman, E., Borow, N., and Stavi, I.: Long-term effects of water harvesting systems on soil and vegetation dynamics in a semiarid region, Israel, 17th Plinius Conference on Mediterranean Risks, Frascati, Rome, Italy, 18–21 Oct 2022, Plinius17-17, https://doi.org/10.5194/egusphere-plinius17-17, 2022.

Irrigation in the Mediterranean region consumes at least 80% of the total water consumption. This is expected to increase due to the impacts of climate change. There is a lack of data regarding the irrigation needs of agricultural plants especially in the Mediterranean region.  To address this issue, the Water Use Efficiency of an Avocado plantation in Crete, Greece is being assessed in systematic way in order to minimize the environmental footprint and impact of the operation while maximizing the benefits for the farmer and the environment. A hydrologic and plant monitoring station have been established in an avocado plantation to determine optimal irrigation schemes, the water use efficiency of the trees and ways to improve plant productivity. The station consists of a precipitation and meteorological station, soil moisture profilers near and away from the tree, irrigation flow monitoring, NDVI and PRI cameras for the estimation of the above ground biomass changes.  These data that are collected every 15 minutes, together with expert knowledge were used to determine optimal irrigation schemes such as deficit irrigation that will conserve the use of water as well as maximize plant production.  The plants were irrigated the amount estimated by their evapotranspiration needs.  In addition, drip irrigation was not applied in a linear fashion in the field, but in a circle with one-meter diameter from the root of the tree.  In this way, the amount of irrigation used was only 30% of the typically prescribed irrigation needs for the plants on an areal basis. Irrigation was applied every 3-4 days based on soil moisture changes in a constant fashion.  It has been observed the over-irrigation stresses the plant. Biomass production was monitored with the NDVI and PRI cameras in order to estimate the above ground production as well as to identify the conditions that plants were stressed. No tilling was practiced in order not to disturb the formation of water stable aggregates and thus the productivity of the soil. Finally, soil organic matter was added by cutting the grass grown in between the trees and leaving the clippings on site and also by not removing the leaves from the avocado. The addition of organic matter in the soil promotes the below ground biodiversity as well as the productivity of the plants and it improves the soil water retention capacity. The results of this study illustrate that we can reduce the amount of irrigation significantly (60-70% of suggested irrigation annual rates) by both increasing the soil organic matter and by irrigating the tree and not the field. Reducing irrigation rates as well increasing the soil water retention capacity can be the two main adaptation strategies that can address effectively the increases or irrigation demand due to climate change.

How to cite: Nikolaidis, N., Efstathiou, D., and Lilli, M.: Adaptation strategies to address irrigation demand in the Mediterranean under climate change, 17th Plinius Conference on Mediterranean Risks, Frascati, Rome, Italy, 18–21 Oct 2022, Plinius17-25, https://doi.org/10.5194/egusphere-plinius17-25, 2022.

One of the research topics in the eLTER-PLUS project is to study the impact of drought events on ecosystem water-use efficiency (WUE) and resilience, and the relationships between WUE, soil structure, plant productivity and ecosystem resilience. Data from 10 well-instrumented eLTER sites across a range of climatic, geological and socio-ecological regions are being used to test resilience indicators, such as WUE, nutrient use efficiency, soil structure and function. Outputs from integrated models that consider the whole water-soil-plant system are being analysed to a) assess the impact of drought events on the WUE of ecosystems, b) determine the resilience of the ecosystems with respect to their ability to recover from impacts of single & multiple droughts, and c) understand the relationship between WUE, soil structure, plant productivity and ecosystem resilience. We also develop mitigation measures for drought adverse impacts. First, we did a time series analysis of CO2 and H2O fluxes from long term Flux tower Eddy Covariance measurements and calculated the evolution of WUE in time and assessed the impact of hydrologic and meteorological droughts on WUE. Second, we conducted modeling simulations of the plant-soil-water system at selected sites and assessed the relationship between WUE and soil structure, plant productivity and ecosystem resilience using the 1D-ICZ and the CLM5.0 models. The presentation will provide an overview of the results across Europe with a specific focus on the Mediterranean sites.

How to cite: Nikolaidis, N., Lilli, M., Efstathiou, D., Poppe, C., and Vereecken, H.: Impact of drought events on plant Water Use Efficiency, 17th Plinius Conference on Mediterranean Risks, Frascati, Rome, Italy, 18–21 Oct 2022, Plinius17-28, https://doi.org/10.5194/egusphere-plinius17-28, 2022.

Higher temperatures, less reliable precipitation patterns, and increased occurrence of extreme events such as drought will significantly affect the sustainability of agricultural systems in the Mediterranean region. A multidisciplinary, participatory approach and a large amount of data are required to unravel the complexity of climate change and properly evaluate the impacts and the possible adaptation strategies. The European countries of the Mediterranean are interesting case studies for these processes since there are numerous institutions active on these topics, collecting a high amount of information. The study area selected for this research is composed of coastal watersheds of Central and Southern Tuscany, Italy. The main objective was to study the impacts of climate change and possible adaptation strategies, with a particular focus on drought. Therefore, a drought risk assessment was performed as a preliminary study to assess the hazard, exposure, vulnerability, and risk of agricultural systems. Free, ready- and easy-to-use data were obtained from public databases to calculate the forty-two indicators that were selected to estimate the various components of risk. Finally, archetype analysis, an emerging approach for identifying recurrent patterns within cases and supporting a context-specific generalization of insights, was used to link the study's results with possible adaptation strategies. Then, the hydrological model SWAT+ was applied to the Ombrone watershed, the largest and most representative of the study area, to estimate impacts on both hydrology and crop production and to evaluate possible agronomic adaptation strategies. By using a hydrological model that includes a module to simulate plant growth, it is possible to study these dynamics at a larger scale than the field scale; this is convenient, especially when dealing with the water resource which is better studied at the watershed level. Data from various public databases were used to set up the model; after that, it was calibrated with monthly streamflow and crop yield of the most representative crops of the area. The future risks for agricultural systems were then analysed by using a multi-model ensemble of EURO-CORDEX projections. The impacts related to the water resource were estimated by evaluating the components of the water balance, while those on agriculture by considering crop yield. Then, possible adaptation strategies such as conservation agriculture and supplemental irrigation were simulated. The presented research demonstrates the importance of integrating multiple data sources and methodologies for the study of climate risks in agricultural systems.

How to cite: Villani, L., Castelli, G., Addisu Yimer, E., Piemontese, L., van Griensven, A., Penna, D., and Bresci, E.: Evaluating agricultural risks in Central Italy by coupling drought risk assessment and agro-hydrological modelling, 17th Plinius Conference on Mediterranean Risks, Frascati, Rome, Italy, 18–21 Oct 2022, Plinius17-35, https://doi.org/10.5194/egusphere-plinius17-35, 2022.

Fires are a natural part of many ecosystems, constituting nonetheless a serious threat to ecosystems and humans. Portugal is recurrently affected by wildfires, being considered a fire-prone region within the Mediterranean basin. However, during the last twenty years, several fire seasons recorded a large extension of burned areas, and the catastrophic fire season of 2017 stands out by recording more than 450,000 hectares of burned area and causing the death of more than 100 people.

Hot and dry fuel conditions were pinpointed as the main drivers of the widespread propagation of wildfires. Therefore, this work aims to assess the impact of the compound or cascading extreme events on vegetation, and also if there was a selectivity of fires for more stressed vegetation. We analyse the climatological and ecological conditions during the pre-fire season, in order to understand its effects on fire season burned areas through fuel accumulation and dryness.

The study highlights the importance of fuel accumulation during the growing season in fire-prone regions like Portugal. Moreover, anomalous hot and dry conditions during summer, in conjunction with strong fuel accumulation during the months preceding fire season, enabled to clarify why the 2017 fire season were so outstanding. Additionally, under the context of climate change, fire seasons as the one occurred in 2017 in Portugal can be more frequent. Therefore, our results highlight that fuel management can be an effective way to mitigate extreme fire seasons and point to the need of implementation of fire prevention policies, especially regarding biomass accumulation control during pre-fire season.

This study was supported by national funds through FCT (Fundação para a Ciência e Tecnologia, Portugal) under the project FIRECAST (PCIF/GRF/0204/2017) and by the 2021 FirEUrisk project funded by European Union’s Horizon 2020 research and innovation programme under the Grant Agreement no. 101003890.

How to cite: Ermitão, T., Gouveia, C., Bastos, A., and Russo, A.: Compound impact of anomalous vegetation activity and hot/dry conditions during the 2017 extreme fire season in Portugal, 17th Plinius Conference on Mediterranean Risks, Frascati, Rome, Italy, 18–21 Oct 2022, Plinius17-70, https://doi.org/10.5194/egusphere-plinius17-70, 2022.

The Mediterranean basin is strongly affected by global warming leading to important changes in the hydrological cycle and ecosystems. Mean precipitation decrease in the western Mediterranean reduces water availability in the region yielding, together with air temperature increase, loss of forests and desertification. Besides, extreme conditions linked to climate change play an important role in the occurrence of fires enhancing the loss of forest areas. Forests provide an important amount of water vapor to the atmosphere, can help decrease air temperature, and they are crucial in carbon dioxide fixation. In these terms, Mediterranean countries such as Spain, strongly affected by climate change, started reforestation efforts at local-to-regional scales to adapt and mitigate its effects. However, it is key to investigate to what extent these land-use changes influence main hydrometeorological variables and atmospheric dynamics.

In this study, the Weather Research and Forecasting (WRF) model is used to conduct sensitivity analyses regarding the impact of increasing forest mass on the hydrological cycle and atmospheric conditions over the Iberian Peninsula and particularly the Mediterranean coast. To this end, land-use categories have been modified over a control simulation to describe different scenarios. These scenarios are selected regarding the extension of reforested areas, as well as the type of vegetation planted, which are defined with respect to climatological parameters such as mean annual precipitation. The scenarios considered are as follows (i) reforestation with pine forest of bare soils, grasslands and shrublands (PINE1), (ii) same as PINE1 but also reforesting mixed cropland/natural areas (PINE2), (iii) same as PINE2 but with heterogeneous forest (MIXED) and (iv) same as MIXED but with 50% decrease in tree density (MIXED50%). Simulations are conducted at horizontal resolutions of 9 and 3 km for the period 2015-2020 covering the Iberian Peninsula and the Hydrographic Confederations of the Júcar and Segura (CHJS) located in the south-eastern part of the Iberian Peninsula, respectively. The study focuses on the analysis of the spatio-temporal patterns of the main hydrometeorological variables (e.g., precipitation, soil moisture, evapotranspiration and atmospheric water vapor), and the examination of the variability on the chain of processes leading to precipitation.

Preliminary results indicate a generalized increase in annual mean precipitation over the Iberian Peninsula (up to 1% for MIXED), more marked along the Mediterranean coast, together with changes in the distribution of atmospheric water vapor. Main precipitation variations occur during summer, with areas receiving up to three times more precipitation than in the control runs during autumn, some areas near the Mediterranean coast present an increase in seasonal precipitation up to 70% with respect to the control run.

How to cite: Benetó, P., Moutahir, H., and Khodayar, S.: Reforestation efforts and impact on climate change, 17th Plinius Conference on Mediterranean Risks, Frascati, Rome, Italy, 18–21 Oct 2022, Plinius17-90, https://doi.org/10.5194/egusphere-plinius17-90, 2022.

Even though a large part of the Italian peninsula is characterized by a Mediterranean climate intrinsically highly suitable for olive and grapevine cultivation, farmers may experience variable agronomic and management costs due to interannual yield variability. A synoptic picture of major climate stressors and their ongoing impacts on olive and grapevine yield variability at a broad spatio-temporal scale are scarce, but, if identified, could enhance the development of actionable services to alert stakeholders of potential climate risks. We analyzed Italian olive and grapevine yield data from the Italian National Statistics Institute (ISTAT), aggregated at the provincial level, during 2006-2021, and several climatic variables from Reanalysis v5 (ERA5) of the European Centre for Medium-Range Weather Forecasts (ECMWR) to i) explore yields trends and inter-annual variations over the whole peninsula; ii) identify major climate stressors likely responsible for the largest drops in yield; iii) build a composite index that summarizes the risk of having exceptionally low yields due to the occurrence of multiple climate stressors. To this end, we defined two major classes of yield, namely exceptionally low and high yields (^LY and ^HY, respectively), and explored the climatic variables, aggregated on a monthly (grapevine) and bimonthly (olive) time scale, determining yield in outcomes. It is worth noting that the use of monthly or bimonthly periods provides a means of examining the seasonal effects of stressors while providing the basis for near-real-time forecasting. Selected years, characterized by a conspicuous number of both ^LY and ^HY, were focused to examine whether the composite risk index has application at more local scales. Results are discussed and some possible explanations based on the current knowledge of olive and grapevine physiological developmental. We suggest our approach as a promising yet still in-progress work that could pave the way to an integrated meteorological seasonal forecast system to provide timely insight on factors affecting within-season yield development.   

How to cite: Di Paola, A., Di Giuseppe, E., and Pasqui, M.: Climate stressors' interplays modulating interannual olive and grapevine yields in Italy: a composite index approach, 17th Plinius Conference on Mediterranean Risks, Frascati, Rome, Italy, 18–21 Oct 2022, Plinius17-92, https://doi.org/10.5194/egusphere-plinius17-92, 2022.