Impacts on water resources produced by climate change can be exacerbated when occurring in regions already presenting low water resources levels and frequent droughts, and subject to imbalances between water demands and available resources. Within Europe, according to existing climate change scenarios, water resources will be severely affected in Spain. However, the detection of those effects is not simple, because the natural variability of the water cycle and the effects of water abstractions on flow discharges complicate the establishment of clear trends. Therefore, there is a need to improve the assessment of climate change impacts by using hydrological simulation models. This paper reviews water resources and their variability in Spain, the recent modelling studies on hydrological effects of climate change, expected impacts on water resources, the implications in river basins and the current policy actions. Editor Z.W. Kundzewicz Citation Estrela, T., Pérez-Martin, M.A., and Vargas, E., 2012. Impacts of climate change on water resources in Spain. Hydrological Sciences Journal, 57 (6), 1154–1167.

Sea level rise (SLR) produced by climate change affects severely coastal ecosystems which are currently being impacted by sea level rise in many parts of the world. In relation with coastal wetlands, the most relevant induced effect will occur on water and soil's salt content, especially in areas below sea level. This could lead into a reduction of habitat for the wetlands' biota. In this context, this research assesses the SLR related risk in the Júcar River Basin District (JRBD). Hazard, exposure, impact, vulnerability, and risk maps have been elaborated. The design and application of measures is prioritized in those areas classified as Very High risk with the aim of improving coastal ecosystems' climate change adaptation. In Western Mediterranean coast, average sea level (ASL) will rise 0.16 m (2026-2045) and 0.79 m (2081-2100) referred to the reference period (1986-2005). High-end scenarios indicate that ASL will rise 1.35 m-1.92 m (2081-2100). The risk analysis results show that 90% of JRBD area affected by SLR, corresponds to coastal wetlands. Half of the affected area belongs to L'Albufera de Valencia wetland with 32.44 km² below sea level, which represents a water volume of 42.64 hm³ (2026-2045) and a surface between 72.53 and 138.96 km² representing from 118.36 to 289.70 hm³ (2081-2100). In the case of L'Albufera de Valencia the impact will be throughout the 21st century, the average rate of SLR will leap from 4 to 11 cm per decade, therefore MSL will reach the current wetland levels by 2040-2045. This makes necessary to modify the lake's management rules, which will lead to an increase of 40 hm3 in water storage and a reduction in water's renewal time compared to current rates (from 15 to 5 times a year).

Eutrophication is a significant threat to aquatic ecosystems worldwide, and the Mar Menor hypersaline lagoon exemplifies a coastal lagoon at risk of algal blooms due to excessive nutrient loads, nitrogen, and phosphorus. These nutrients originate from various sources within the lagoon’s catchment area, including urban, agricultural, and livestock activities. Regular and occasional loads—during flood events—produce algal blooms that can significantly reduce the water oxygen content and cause massive mortalities, as observed in recent years. A daily algal growth model (Mmag) was developed to better understand the processes and determine key elements such as the phosphorus water–sediment interchange and deep water plants that effect the entire ecosystem and algal growth. The analysis developed can be applied in other wetlands around the world facing similar challenges. In the Mar Menor, both nitrogen and phosphorus have high relevance depending on the period of the year and the phosphorus legacy in the sediments. Floods are the main phosphorus input to the lagoon (80–90%), which goes to the sediment and is released after during the warm months in the following years. At the end of summer, phosphorus released from the sediment and the regular nitrate inputs to the lagoon increase the algal bloom risk. The good status of deep water plants, which reduces the phosphorus release in summer, is a key element to reduce the algal bloom risk. An integrated set of measures is required to reduce the mean chlorophyll to levels under 1 or 0.5 µgChla/L that can make the Mar Menor more robust and resilient.