Surface-water availability, defined as precipitation minus evapotranspiration, can be affected by changes in vegetation. These impacts can be local, due to the modification of evapotranspiration and precipitation, or non-local, due to changes in atmospheric moisture transport. However, the teleconnections of vegetation changes on water availability in downwind regions remain poorly constrained by observations. By linking measurements of local precipitation to a new hydrologically weighted leaf area index that accounts for both local and upwind vegetation contributions, we demonstrate that vegetation changes have increased global water availability at a rate of 0.26 mm yr−2 for the 2001–2018 period. Critically, this increase has attenuated about 15% of the recently observed decline in global water availability. The water availability increase is due to a greater rise in precipitation relative to evapotranspiration for over 53% of the global land surface. We also quantify the potential hydrological impacts of regional vegetation increases at any given location across global land areas. We find that enhanced vegetation is beneficial to both local and downwind water availability for ~45% of the land surface, whereas it is adverse elsewhere, primarily in water-limited or high-elevation regions. Our results highlight the potential strong effects of deliberate vegetation changes, such as afforestation programmes, on water resources beyond local and regional scales.

Afforestation, particularly plantation forestry, has emerged as a key land-use strategy in Australia, supported by government and industry initiatives such as the Plantations 2020 Vision. While plantations offer significant economic and environmental benefits—including carbon sequestration and salinity control—their impact on catchment-scale hydrology remains a critical concern. This report examines the hydrological consequences of afforestation, with a focus on changes to water yield and river salinity in a national context where water resources are under increasing stress.

The study explores how afforestation affects the volume and timing of catchment runoff, and its implications for river salinity, particularly in regulated and over-allocated river systems such as the Murray-Darling Basin. With afforestation capable of significantly reducing groundwater recharge and surface runoff, the expansion of plantations may inadvertently conflict with national water reform goals, including the Cap on Diversions, The Living Murray Initiative, and the National Water Initiative.

The report also outlines management strategies to balance the benefits of plantation development with sustainable water resource use. It emphasizes the need for regulatory planning and hydrological assessment tools to ensure plantation expansion does not compromise environmental flows or water entitlements. Ultimately, the report aims to inform land and water managers of the potential trade-offs involved in afforestation, supporting more integrated, catchment-scale decision-making.

Forest restoration emerges as a sustainable practice to counteract biodiversity loss and enhance ecosystem services such as carbon sequestration and water quality improvement. However, more research is necessary on the hydrological effects of forest restoration under different strategies such as tree species options. In this study, we investigate how afforestation with longleaf pine (Pinus palustris) and loblolly pine (Pinus taeda L.) may affect the full hydrologic cycles including precipitation (P) and water quality across two large watersheds: the Alabama-Coosa-Tallapoosa (ACT) and Tombigbee-Black Warrior (TBW) river basins in the southeast United States. To capture the impacts of afforestation on precipitation, we leveraged the Soil and Water Assessment Tool (SWAT) model and a local moisture recycling ratio (LMR) dataset to establish a relationship between model-simulated evapotranspiration (ET) and LMR. Longleaf pine and loblolly pine have contrasting forest structure characteristics that affect model parameters and hydrological responses. Results showed that afforestation with longleaf pine increased mean annual ET by 3 % (25 mm/year) and 6 % (48 mm/year) across the ACT and TBW watersheds, respectively. As a result, mean annual streamflow decreased by 3.3 % (18 mm/year) and 1.6 % (11 mm/year) in the ACT and TBW watersheds, respectively. In contrast, afforestation with loblolly pine led to larger increases in mean annual ET of 17 % (131 mm/year) and 10 % (79 mm/year) in affected areas in the ACT and TBW watersheds, respectively. As a result, mean annual streamflow decreased by 5.2 % (29 mm/year) and 2.8 % (19 mm/year) at the watershed level in the ACT and TBW watersheds, respectively. Overall, the afforestation scenarios led to decreases in watershed-scale sediment and nutrient exports, especially under longleaf pine afforestation. Large-scale afforestation had negligible effects on precipitation via local moisture recycling at the watershed scale. Our study indicates that the choices of tree species and forest structure are important to water yield in the southeastern U.S. and that moisture recycling has minor influences on the local water cycle of the study region.

Human use and alteration of land has profound effects on the environment, both locally where it takes place, and at the planetary scale via climate change and other mechanisms. This building block explains what is meant by land use and land use change, both direct and indirect.