| 23 Mar 2026
Impacts of land-use and land-cover change on blue–green water partitioning
Abstract. Land-use and land-cover change (LULCC) is a major driver of terrestrial water cycle changes, yet its effects on how precipitation is partitioned into blue (runoff) and green water (transpiration) flows remain unclear. Here we address this knowledge gap using Earth system model simulations from the Land Use Model Intercomparison Project (LUMIP) under contrasting socioeconomic pathways (SSP1-2.6 and SSP3-7.0). We find that future sustainable LULCC (i.e., predominantly avoided deforestation and preservation of natural non-forest ecosystems) significantly impacts blue-green water partitioning, with regions showing positive leaf area index (LAI) and gross primary productivity (GPP) responses generally corresponding to larger green water shares. These effects are strongest in the tropics and particularly during dry seasons, where LAI and GPP responses are largest. Regions with the strongest green water gains show the highest sensitivity of blue-green water partitioning to vegetation responses, with the largest partitioning shifts per unit change in LAI or GPP. Precipitation responses to LULCC further modulate the strength of blue–green water partitioning shifts. In some regions, higher transpiration is partly offset by increased rainfall, limiting reductions in blue water availability. While we find consistent ecohydrological responses to LULCC across the multi-model ensemble mean, substantial regional inter-model disagreement arises due to differences in model-specific plant functional types and their parametrisations. Our results underscore that the water cost or benefit of land management depends jointly on vegetation function, precipitation feedbacks, and model structural uncertainty.
General comments
The paper provides a rich global-scale analysis of effects of land use and land cover change (LULCC) upon the partitioning of blue and green water flows, using a LUMIP model ensemble in different setups (focused on a ‘sustainable LULCC’ scenario). The analysis appears to be well done and plausibly interpreted, with a quite detailed examination of process interactions, regional features, and model uncertainties. That said, the Results and Discussion are rather dense with much information, parts of which could be portrayed in a somewhat more accessible way. Below I provide some comments on how to possibly achieve this. Overall, may comments are relatively minor and could be addressed mainly by some clarifications and restructurings.
Specific comments
The Abstract should clarify that you mainly analyze transpiration (as a representative of green water) rather than total evapotranspiration. While outputs for evaporation appear to have been analyzed also, I do miss a short discussion of whether a full inclusion of evapotranspiration (not just transpiration) in the ratio would produce relevantly different results.
Please state whether (and how) the direct effects of increasing carbon dioxide concentrations upon vegetation productivity / coverage and upon transpiration is considered in the models. No need to separately quantify the particular contributions of these effects here, but at least some words on this would be helpful (in the Discussion); i.e. is transpiration suppressed a lot under SSP3-7 / high CO2 concentrations. Relatedly, the UKESM model simulates “dynamic PFT competition” while in other models vegetation distribution is prescribed (according to Table 1). Does this have implications for results from that particular model?
Sections 3.1 and 3.2 contain a lot of information with many acronyms etc. Is it possible to provide a table listing the model experiments (that could also be used to remind the reader of the different setups analyzed) and key results for each, such as the correlations, global areas affected by change XY, or something similar? Then the table could be pointed to for these results rather than mentioning them all in the text.
Besides, if there is need for shortening the length of the text, section 3.3 is a candidate; it is a regional zoom of the analysis providing much detail, maybe not all of it required to get the main messages across.
At the beginning of the Discussion, the key results could be highlighted again as bullet points, and then – which I would definitely recommend – the Discussion should have some subtitles for each of these points (like green water shares, teleconnections, uncertainties, limitations). This would be another, easy-to-implement way to highlight once more the main results and to guide the reader through the large amount of information.
Technical corrections – none.