Assessment of the water supply:demand ratios in a Mediterranean basin under different global change scenarios and mitigation alternatives

Abstract

Spatial differences in the supply and demand of ecosystem services such as water provisioning often imply that the demand for ecosystem services cannot be fulfilled at the local scale, but it can be fulfilled at larger scales (regional, continental). Differences in the supply:demand (S:D) ratio for a given service result in different values, and these differences might be assessed with monetary or non-monetary metrics. Water scarcity occurs where and when water resources are not enough to meet all the demands, and this affects equally the service of water provisioning and the ecosystem needs. In this study we assess the value of water in a Mediterranean basin under different global change (i.e. both climate and anthropogenic changes) and mitigation scenarios, with a non-monetary metric: the S:D ratio. We computed water balances across the Ebro basin (North-East Spain) with the spatially explicit InVEST model. We highlight the spatial and temporal mismatches existing across a single hydrological basin regarding water provisioning and its consumption, considering or not, the environmental demand (environmental flow). The study shows that water scarcity is commonly a local issue (sub-basin to region), but that all demands are met at the largest considered spatial scale (basin). This was not the case in the worst-case scenario (increasing demands and decreasing supply), as the S:D ratio at the basin scale was near 1, indicating that serious problems of water scarcity might occur in the near future even at the basin scale. The analysis of possible mitigation scenarios reveals that the impact of global change may be counteracted by the decrease of irrigated areas. Furthermore, the comparison between a non-monetary (S:D ratio) and a monetary (water price) valuation metrics reveals that the S:D ratio provides similar values and might be therefore used as a spatially explicit metric to valuate the ecosystem service water provisioning.

Effect of National-Scale Afforestation on Forest Water Supply and Soil Loss in South Korea, 1971–2010

“…In particular, this model was developed to provide decision makers with a trade-off of ecosystem services to compare the impacts of the changes in land cover or climate [30]. InVEST Water Yield (InVEST-WY) is one of the modules of the InVEST model to estimate water supply, demand and hydropower [31,32] and has been used in previous studies in Korea [33,34]. This study aims to identify the time series changes in forest water supply; thus, the InVEST-WY model was considered the most appropriate one as it allows the spatial-temporal change analysis.…”

“…There is no change in other land cover types, but the forest area has been reconstructed Sustainability 2017, 9, 1017 6 of 18 every year. The coefficients of the biophysical table were determined according to the land cover information, and the K c coefficients of the forest area were set to 1 based on the previous studies [31,32].…”

Uncertainty analysis of a spatially explicit annual water-balance model: case study of the Cape Fear basin, North Carolina

“…They found that the model was sensitive to climate variables, but less so to the Z parameter (see model description). Similarly, Boithias et al (2014) and Terrado et al (2014) reflect on the sensitivity of the model to climate inputs and calibrate the model based on the climate parameters and return flows. The conclusions of these studies are often context-specific and lack a quantitative estimate of the model's structural uncertainties.…”

Simulating past changes in the balance between water demand and availability and assessing their main drivers at the river basin scale

“…The spatial distribution of water demand and availability was mapped to correctly reproduce the spatial heterogeneity of water shortage in each study area: water stress assessments can vary depending on the spatial or temporal scale (Boithias et al, 2014). Thus, it is essential to properly account for the main heterogeneities in water demand and availability.…”