Sand dams for sustainable water management: Challenges and future opportunities.

Sand dams are impermeable water harvesting structures built to collect and store water within the volume of sediments transported by ephemeral rivers. The artificial sandy aquifer created by the sand dam reduces evaporation losses relative to surface water storage in traditional dams. Recent years have seen a renaissance of studies on sand dams as an effective water scarcity adaptation strategy for drylands. However, many aspects of their functioning and effectiveness are still unclear. Literature reviews have pointed to a range of research gaps that need further scientific attention, such as river corridors and network dynamics, watershed-scale impacts, and interaction with social dynamics. However, the scattered and partially incomplete information across the different reviews would benefit from an integrated framework for directing future research efforts. This paper is a collaborative effort of different research groups active on sand dams and stems from the need to channel future research efforts on this topic in a thorough and coherent way. We synthesize the pivotal research gaps of a) unclear definition of "functioning" sand dams, b) lack of methodologies for watershed-scale analysis, c) neglect of social aspects in sand dam research, and d) underreported impacts of sand dams. We then propose framing future research to better target the synthesized gaps, including using the social-ecological systems framework to better capture the interconnected social and biophysical research gaps on sand dams, fully utilizing the potential of remote sensing in large-scale studies and collecting sand dam cases across the world to create an extensive database to advance evidence-based research on sand dams.

Water Ecosystem Services Footprint of agricultural production in Central Italy.

The appropriate implementation of the concept of Water-related Ecosystem Services (WES) in water resources planning can support the development of productive activities and, at the same time, sustain local ecosystems. However, such implementation it is only possible when both WES supply and demand are evaluated, eventually with a spatially explicit method, for gaining insights into the ecohydrological behavior of a basin and the anthropogenic pressures on the available water resources. Based on the integration of hydrological modelling and Water Footprint (WF) analysis, this study aims at developing a methodology to analyze both the supply and demand of WES, evaluating a Water Ecosystem Services Footprint (WESF) associated with the agricultural sector. The proposed methodology is based on a 3-tiered approach: 1) evaluating the WES demand determined by the agricultural sector using the WF Assessment methodology; 2) quantifying the WES supply by applying the Soil Water Assessment Tool (SWAT); 3) estimating the green, blue, and gray WESF through dedicated indicators in order to identify the main hotspots. The methodology is applied to a specific case study in the upstream part of the Arno river basin (Central Italy). By means of subnational WF statistics the green, blue, and gray WF of the agricultural sector is calculated, determining the spatial distribution of WES demand in the catchment. SWAT results quantify the available water resources, pointing out the blue/green surface water partitioning, where precipitation is divided into 25% runoff and 46% evapotranspiration, and the associated WES supply. Merging the results, the WESF spatial pattern is evaluated, properly identifying the most critical areas in the catchment. WESF represents an operative tool to look at agricultural water management from an ecosystem-based perspective, supporting the identification of the strategies to explore the sustainable coupling of biosphere and anthroposphere.

Evidence-Based Integrated Analysis of Environmental Hazards in Southern Bolivia.

The "Valles Cruceños" rural region plays a fundamental role for securing food and other resources for the neighboring, and fast sprawling, city of Santa Cruz de la Sierra (Bolivia). Due to the increasing pressure on its natural resources, the region is affected by progressive and severe environmental degradation, as many other rural regions in South and Central America. In this situation, sound policies and governance for sustainable land management are weak and not supported by data and scientific research outputs. With the present study, we aim at developing a novel and practical integrated hazard analysis methodology, supporting the evidence-based understanding of hazard patterns and informing risk assessment processes in the urban-rural continuum. Firstly, the main environmental hazards affecting the area were identified via questionnaire campaigns, held by the staff of local municipalities. Focusing on the hazards mostly perceived by the inhabitants of the region, including deforestation, water pollution and precipitation changes, hazard maps were created by using multiple environmental hazards indicators. An integrated hazard map was then built in a GIS environment, after a pair-wise comparison process. The maps represent a first baseline for the analysis of the present status of natural resources in "Valles Cruceños" area, and the proposed approach can be scaled up for integrated environmental hazards analysis in similar areas of Latin America.

Fog collection as a strategy to sequester carbon in drylands.

Advection fog is the sole source of water for many near-the-sea arid areas worldwide such as the lomas, i.e. fog-dependant landscapes of the coastal zone of Peru and Northern Chile, where deforestation occurred since 16th century, leading to a progressive and severe desertification. There, today's local socio-ecological systems suffer from lack of freshwater because they cannot rely anymore on the contribution of fog captured by vegetation. This paper presents the results of an experimental reforestation project carried out in Mejia (Peru), where tree seedlings of five native and exotic species were planted in two permanent plots in 1996. Part of the seedlings were irrigated during the first three years after planting, others not. The irrigation was carried out thanks to water harvesting by large fog collectors. From the third year onwards, all trees relied only on fog water collected by their canopy. Survival rate, height, and root-collar diameter were monitored until 2010, when also the soil carbon and nitrogen stocks were measured. Fifteen years after the planting, about 65% of trees were still alive and growing, and reforestation had induced substantial carbon sequestration both above- and below-ground. Of the tree species, Acacia saligna was definitely best performing than the other, with most of the above ground carbon stored in its biomass and a consequent high efficiency as natural fog collector. Overall, the combination of fog collection by nets and the plantation of trees showing good fog collection capacity, represented a successful strategy for allowing reforestation of arid environments and induced fast and substantial carbon sequestration. Greater efforts should be thus devoted for this purpose, paying special attention to the selection of the most suitable tree species to plant, especially looking at the local biodiversity. This work is dedicated to the memory of Professor Mario Falciai, passed away in 2015, who firstly conceived the experiment and attended all the work since 1996, bringing in our University the idea of Fog Collection for sustainable water management.