Observedhuman-induced climate changes have been changing precipitation and temperaturepatterns, affecting the quantity and quality of freshwater resources foragriculture and forestry.
The impacts related with water use, and mainly theimpact of green water flows, are particularly relevant for agricultural andagro-forestry based products, depending on local land-use and land coverchanges. Green water flows refer to the portions of green water (from rain)used by vegetation that is evaporated or transpired. This is an on-going research issue in Life Cycle Assessment(LCA), since the environmental mechanisms of green water consumption are notyet well understood. These mechanisms are: (1) potential disturbances ofregional long-term availability of surface blue water (called as green waterand soil interface) due to changes in green water use, and; (2) potentialperturbations in the evaporation and transpiration (ET) that is recycled intothe atmosphere, and then, in the rainfall that returns to the regionalterrestrial ecosystem (called as green water and atmosphere interface), due toland covers [1,2].
With current climateconditions, the developed characterization factors (CFs) to the midpoint greenwater scarcity LCA impact category (ranging from 0.01 to 1 mm/mmeqor ) for both interfaces at 0.5 degrees global domainshows high variability, mostly in the northern hemisphere. This means that thishemisphere already experiences reduction of green water flows recycled to the atmosphere,potentially affecting regional rainfall levels to maintain agriculture andforestry. In addition, some regions of the northern hemisphere alreadyexperience disturbances in the production of surface blue water.
Thisstudy is devoted to evaluate the changes in the green water scarcity CFs for afuture climate projections downscaled to Portugal from the CMIP5 earth systemmodel MPI-ESM, using the Weather Research and Forecasting model. The futureclimate the Representative Concentration Pathway RCP 8.5 scenario has beenadopted. RCP8.5 was developed in the assumption that the greenhouse gasemissions and concentrations will considerably increase over time, leading to aradiative forcing of 8.5 W m−2 at the end of the century (2100).This scenario is considered by the scientific community to reflect the worstset of expectations with the most onerous impacts. Precipitation levels willdecrease around 1 to 5 mm/day in Portugal (mainly during Spring and Autumn) ina future climate. Green ET depends directly on precipitation,therefore, the effective mean annual green ET decreases under future climate,leading to perturbations to both interfaces under study.
The green water scarcity CFs, for bothinterfaces show high variability under future climate. These changes in the CFs allow to the waterfocused-LCA methodology, assessing the actual and future magnitude of potentialimpacts related to green water. The results show that green water availabilitywill be decreased under future climate, increasing disturbances in the productionof surface blue water, and reducing green water flowsrecycled to atmosphere. In this sense, some measures to increase thesoil water holding capacity, protecting green water required to agriculture andforestry activities, should be applied. For example, the use of organic mulchincreases the level of organic matter in the soil, which results in theincrease of the water holding capacity, due to the affinity of organic matterfor water. Also, rainwater harvesting in farms dams for livestock watering andcrops irrigation is of particular relevance in arid and semi-arid regions, which are prone to droughts.
4a. Predictions and responses
