This study explores the potential of Sentinel-1 Synthetic Aperture Radar (SAR) to identify phenological phases of wheat, sugar beet, and canola. Breakpoint and extreme value analyses were applied to a dense time series of interferometric (InSAR) and polarimetric (PolSAR) features recorded during the growing season of 2017 at the JECAM site DEMMIN (Germany). The analyses of breakpoints and extrema allowed for the distinction of vegetative and reproductive stages for wheat and canola. Certain phenological stages, measured in situ using the BBCH-scale, such as leaf development and rosette growth of sugar beet or stem elongation and ripening of wheat, were detectable by a combination of InSAR coherence, polarimetric Alpha and Entropy, and backscatter (VV/VH). Except for some fringe cases, the temporal difference between in situ observations and breakpoints or extrema ranged from zero to five days. Backscatter produced the signature that generated the most breakpoints and extrema. However, certain micro stadia, such as leaf development of BBCH 10 of sugar beet or flowering BBCH 69 of wheat, were only identifiable by the InSAR coherence and Alpha. Hence, it is concluded that combining PolSAR and InSAR features increases the number of detectable phenological events in the phenological cycles of crops.

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<p>Remote sensing is recognized as the most feasible means to provide regional information on land surfaces and monitor soil parameters such as soil moisture and evapotranspiration. The use of satellite-derived products can be crucial for groundwater resources in karst aquifers, particularly in regions, such as southern Italy, where groundwater availability drives economic and social development and there is a lack of monitored data. This study aims to expand the classical hydrogeological approach, used for the estimation of groundwater recharge of karst aquifers, to the understanding of the hydrological role of soil coverings by the integration of field monitoring and products derived by remotely sensed data. The research was conducted on the representative Mts. Soprano-Vesole-Chianello karst aquifer (Campania, southern Italy). Copernicus Global Land Services Soil Water Index (SWI) and Moderate Resolution Imaging Spectroradiometer (MODIS) Evapotranspiration products were explored to assess soil water content and evapotranspiration regimes. The analysis included time series gathered by a monitoring network consisting of 5 soil moisture multi-profile probes, working since 2021. The SWI1km provides daily soil water content information at 1 km resolution. Depending on the uncertain calculation, not considering evapotranspiration and soil texture, the SWI1km product provides 8-SWI estimations and the related quality factor values. Instead, the MOD16A2 is based on MODIS data and provides 8-day evapotranspiration estimation at 0.5 km resolution. The product collection is based on the logic of the Penman-Monteith equation, which integrates inputs of daily meteorological re-analysis data along with products derived by (MODIS) including vegetation property dynamics, albedo, and land cover.</p><p>Both products showed zones of no-data occurring across the mountain areas of the karst aquifers. This limitation is related to the algorithms that consider several parameters such as topography (slope aspect and angle) and occurrence of clouds for product generation.</p><p>The primary outcome of this study was the extraction of SWI values and the calculation of a mean value for the 8-SWI values, weighted by the related quality factor (<em>SWI<sub>w</sub></em>). <em>SWI<sub>w</sub></em> showed a constant difference of about -20% in comparison to the daily average values obtained by field monitoring. Despite this discrepancy, the annual trend of the <em>SWI<sub>w</sub></em> was found being very consistent with the soil moisture probe measurements (corr. > 0.68) and displaying a good response to rainfall events.</p><p>Moreover, the MODIS <em>ET</em> data displayed the expected pattern of evapotranspiration with a temporal resolution not achievable in other ways considering the lack of local meteorological data.</p><p>In order to cope with missing data across the mountain areas of the karst aquifer, a spatial interpolation of <em>SWI<sub>w</sub></em> and MODIS <em>ET</em> was carried out by different geostatistical techniques.</p><p>The findings suggest that SWI1km and MODIS16A2 are useful in monitoring soil water content and evapotranspiration of soils covering karst aquifers and controlling groundwater recharge. Although there are limitations due to missing data, both products can be still effectively utilized if properly interpolated. Therefore, they can be considered fundamental for assessing patterns of groundwater recharge in karst aquifers, especially in areas which are not extensively monitored as in the case of southern Italy.</p>

<p>Carbonate aquifers supply freshwater to about one-quarter of the world population. Their particular hydrodynamic behavior is a valuable property for groundwater extraction, on the downside, carbonate aquifers are vulnerable to overexploitation and pollution. Fractures, fissures, and typical karst features, such as  conduits and vertical shafts, create high regional hydraulic conductivities and fast response times to hydrological events, complicating numerical modeling and management of carbonate aquifers in general. Here, we develop a new method to assess the vulnerability of Mediterranean karst aquifers concerning shifts in climate. Particularly, we are interested in 1) which types of karst aquifers are most vulnerable and 2) which factors have the highest impact on their climate vulnerability.</p><p>Our approach is based on a vulnerability index, which is calculated from selected indicators of aquifer behavior that refer to land cover, soil types, wetlands, water demand, current change of groundwater levels, total water volume, run-off, water exploitation index, and freshwater production. First, we calculate vulnerability indices for all karst aquifers – as identified in the World Karst Aquifer Map by the World-wide Hydrogeological Mapping and Assessment Programme (WHYMAP WOKAM v1 database; Chen et al., 2017) – that have at least 90% of their area belonging to Mediterranean climate zones (Csa, Csb, and Csc). Then, we group these aquifers into classes representing different physical behaviors and morphological characteristics (e.g. highly karstified systems in mountainous areas).</p><p>An evident approach to investigate various aquifers in terms of their vulnerability is the development of numerical flow models. The advantage is that the boundary conditions, such as average annual precipitation and temperature, can be modified to consider different climatic scenarios. Thus, the resulting impact on water volumes and the aquifer response can be simulated accordingly. However, this approach requires large amounts of data and high computational costs.</p><p>Our method uses selected sets of karst aquifers representing different variations of Mediterranean climates (i.e. that are similar in terms of temperature and precipitation patterns). These aquifers are compared by analyzing and plotting regional climate variables versus previously calculated vulnerability indices. By identifying and comparing climate-vulnerability relations within aquifer sets, we can mimic changes in climate for individual aquifers in line with the RCP4.5 scenario until 2050. This approach, which relies on present-day observed conditions, allows us to predict the effect of a changing climate on the vulnerability of an aquifer class without the need to develop a complex numerical model.</p><p>The results are visualized in the form of vulnerability maps and used to derive recommendations for the sustainable management of karst aquifers under Mediterranean climates.</p>