Irrigation is an important aspect of agricultural management, with irrigated areas providing ∼40% of global food production over only ∼20% of global cropland (WWAP, 2019). It is fundamental to the food security of less developed countries, where populations have experienced fast growth (Schultz et al., 2005). Since the 1950s, the global irrigated land area has expanded rapidly, thereby increasing worldwide irrigation water demand. Consequently, irrigation currently accounts for ∼90% (∼1,200 km 3 by the end of 20th century) of the global total consumptive freshwater use (

<p>The frequency and severity of droughts and heatwaves are projected to increase under global warming. However, their impacts on the terrestrial biosphere and the anthropogenic CO<sub>2</sub> sink remain poorly understood. Here we analyse the effects of six hypothetical climate scenarios with stationary climate but differing drought-heat signatures on vegetation distribution and land carbon dynamics, as modelled by seven state-of-the-art dynamic global vegetation models. The six forcing scenarios are sampled from a long climate model simulation and consist of a control<em> </em>scenario representing a natural climate, a scenario with no hot and dry extremes, one with no compound hot and dry extremes but univariate extremes are possible, one with only hot extremes, one with only dry extremes, and one with both hot and dry extremes. Models show substantial differences in their vegetation coverage response to the different scenarios. While in some models, climate with no droughts and heatwaves favours tree growth, this is not the case for other models, where grasses benefit. Similarly, climates with frequent droughts promote grasses in some models and reduce forest growth in others. Models tend to agree that a climate with frequent concurrent droughts and heatwaves leads to reduced tree cover and increased grass cover. The changes in coverage are mirrored by changes in gross and net carbon fluxes. The stark differences among model responses illustrate the different modelling processes dealing with heat and drought stress and how they are differently affected by the extremes. Overall, this comparison helps quantify model uncertainties and process differences that are important for how vegetation behaves under extreme climate events.</p><p>Our study illustrates how factorial model experiments can be employed to disentangle the impacts from single and compound extremes. The findings from this model comparison may also help to identify sources of uncertainty in carbon cycle projections.</p>

<p>As the most dominant freshwater-use practice, irrigation plays an important role in global and regional environmental changes. Its extent experienced a substantial increase during the 20<sup>th</sup> century, from less than 100 mha before 1950 to about 300 mha around the year 2000. To advance the scientific understanding of the irrigation-expansion-induced impacts during the last century, we launched a model-intercomparison project (MIP), through which we intend to discover its effects on different sectors, i.e. water, climate, and agriculture, with Earth system models. In the protocol, two experiments are designed, i) simulation with transient irrigation extent and ii) simulation with the irrigation extent fixed at the level of the year 1901. For every experiment, three ensemble members are required to reduce the uncertainty. Currently, the analysis of outputs will be focused on climate extremes, the water cycle, vegetation-carbon interactions and some social implications. In the next phase of IRRMIP, we plan to combine the Earth system model community with both the hydrological model and crop model communities.</p>

<p>Recent observation-based and modelling studies have highlighted the impacts of irrigation on near-surface climate, and it has been stressed that irrigation can alleviate hot extremes, change precipitation patterns and increase air moisture. However, most of the previous studies only focused on historical periods, while potential climate change, land cover conversions and irrigation method advances may alter both the magnitudes and patterns of irrigation-induced effects, thus the influence of irrigation in the future remains uncertain. To address this question, we will employ version 2 of the Community Earth System Model (CESM2) with an updated irrigation scheme considering different irrigation techniques, to detect the impacts of irrigation on near-surface climate under different future scenarios. To include the influence of climate, land cover and irrigation method, several Representative Concentration Pathways (RCP) and Shared Socio-economic Pathways (SSP) scenarios will be selected, and different scenarios of Irrigation Method Distribution (IMD) evolvement will be designed in line with SSP scenarios for this study. Different combinations of RCP, SSP and IMD scenarios will be used to force the model, and the outputs of these experiments will be analysed and compared. We anticipate that our results will reveal how irrigation-induced impacts on near-surface climate will evolve under different scenarios.</p>