Precipitation is essential for food production in Sub-Saharan Africa, where more than 80 % of agriculture is rainfed. Although ∼40 % of precipitation in certain regions is recycled moisture from Africa's tropical rainforest, there needs to be more knowledge about how this moisture supports the continent's agriculture. In this study, we quantify all moisture sources for agrarian precipitation (African agricultural precipitationshed), the estimates of African rainforest's moisture contribution to agricultural precipitation, and the evaporation from agricultural land across the continent. Applying a moisture tracking model (UTRACK) and a dynamic global vegetation model (LPJmL), we find that the Congo rainforest (>60 % tree cover) is a crucial moisture source for many agricultural regions. Although most of the rainforest acreage is in the DRC, many neighboring nations rely significantly on rainforest moisture for their rainfed agriculture, and even in remote places, rainforest moisture accounts for ∼10–20 % of agricultural water use. Given continuous deforestation and climate change, which impact rainforest areas and resilience, more robust governance for conserving the Congo rainforest is necessary to ensure future food production across multiple Sub-Saharan African countries.

The global water cycle has undergone considerable changes since pre-industrial times due to global climate change and land-use changes. These drivers will almost certainly continue to change during the course of this century. However, where, how, and to which extent terrestrial moisture recycling will change as a result remains unclear.

Mutually consistent scenarios of climate change and land-use changes for the 21st century are provided by the Shared Socioeconomic Pathways (SSPs). The SSPs provide a framework of five different narratives involving varying degrees of challenges associated with mitigation or adaptation. From each narrative follow different implications for emissions, energy, and land use. The SSPs serve as the conceptual framework behind the sixth generation of the Coupled Model Intercomparison Project, CMIP6.

Terrestrial moisture recycling is often assessed using atmospheric moisture tracking models. An example is UTrack, a Lagrangian model to track moisture through three-dimensional space. Here we present a new forward-tracking version of UTrack that is forced by output of a CMIP6 model to study how terrestrial moisture recycling may change across the globe until the end of the  21st century in a range of SSPs, from mild to severe: SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5. For this forcing, we chose the Norwegian Earth System Model version 2, or NorESM2. It has a temporal resolution of one day and a spatial resolution of 1.25° × 0.9375° at eight pressure levels.

We find that across the 21st century, the global terrestrial moisture recycling ratio decreases with the severity of the Shared Socioeconomic Pathways (SSPs). We calculate a decrease in global terrestrial precipitation recycling by 2.1% with every degree of global warming. Because the SSPs represent internally consistent scenarios of both global warming and global land cover changes, it is hard to distinguish the relative contributions of these two, but the evidence points at a major influence of global warming on moisture recycling.

We find spatial differences in trends in recycling ratios, but which are broadly consistent among SSPs. If a change in precipitation (either drying or wetting) coincides with an increase in terrestrial precipitation recycling ratio, we call it land-dominated. We call the change in precipitation ocean-dominated if it coincides with a decrease in terrestrial precipitation recycling ratio. Land dominance tends to occur in regions with already large terrestrial precipitation recycling ratios, mainly interior South America (land-dominated drying) and eastern Asia (land-dominated wetting). Land-dominated drying may also happen in eastern Europe, in central America and in subtropical sub-Saharan Africa. Ocean-dominance, mainly in the form of wetting, is found primarily in the high northern latitudes and in central Africa.

We also simulated the changes in basin recycling for the 27 major river basins of the world, confirming the overall tendency of decreasing recycling with severity of the SSP, as well as its spatial variations.

The world and its growing population is faced with the task of addressing rising food insecurities amidst increasing transgressions of planetary boundaries and associated systemic risks arising from links and feedbacks among the boundaries. Here we analyze interactions of the planetary boundaries for climate change and freshwater change, focused on green water (i.e. plant-available soil moisture departures from pre-industrial variability ranges) and discuss potential effects on food security. By forcing the dynamic global vegetation model LPJmL5.8 with an ensemble of 5 CMIP6 climate models under the RCP 7.0 emissions scenario, we detect significant increases in dry deviations for green water in nearly a third of the terrestrial surface area by the end of the century (2071-2100), compared to current levels (period 1985-2014). The transgression of the climate change boundary adversely affects the status of the green water boundary, which is captured by the dynamic risk space terminology that we introduce here. This finding has crucial implications for rainfed agriculture, a food production system exclusively relying on green water, which is currently responsible for more than 60% of global food production. Despite its importance, green water does not feature in global sustainability policy and agreements, so we argue it should be made explicit in the Sustainable Development Goals and their targets. 

Currently, water provision for food production in Africa's agricultural system is primarily focused on blue water estimates, which are typically used in irrigated agriculture. This has resulted in both research and policy focusing on adapting agricultural practices to blue water supply and access from rivers and lakes. and overlooks the equally important role of green water. Green water is defined as the soil moisture available for plant uptake as a result of rainfall infiltration. Africa's food production relies heavily on rainfed agriculture, making green water a crucial resource. However, it is unclear how much green water can contribute to transforming food production through adapted agricultural practices. The aim of our study is to assess the hydroclimatic regime and identify regions dominated by green and blue water at the landscape level. In regions dominated by green water, we also map the potential for additional agriculture through adapted farming practices. We investigate the extent and location of changes in the blue-green water landscape under various climate change scenarios. To achieve this, we employ the LPJmL dynamic global vegetation model to simulate water flows, vegetation growth, crop production, and climate interactions from 1901 to 2100. The simulations indicate that green water has a high potential to enhance food production in agriculture, particularly in semi-arid, semi-humid, and wet sub-humid regions. However, most wet humid regions are already operating at their maximum capacity. The findings also suggest that integrating green water into agriculture, for example, through rainwater harvesting systems, can improve the efficiency of food production, particularly in regions where water efficiency has been low. This highlights the significance of green water and its potential as a crucial water source for enhancing food security in Africa.