Dryland ecosystems cover 40% of our planet’s land surface, support the lives of billions of people, and are responding dramatically to the combined effects of climate and land use change. These expansive and diverse systems also dominate core aspects of Earth’s climate, storing and exchanging vast amounts of water, carbon, and energy with the atmosphere. Despite the indispensable natural resources and ecosystem services provided by drylands and their high vulnerability to change, drylands are one of the most, if not the most, poorly understood ecosystem types. Such lack of study has been in part due to incorrect historical assumptions that drylands are unproductive “wastelands”. This lack of understanding results in notably poor model representation and forecasting capacity, hindering our representation and decision making for these vulnerable ecosystems. The NASA Terrestrial Ecology Program solicited proposals for a multi-year field campaign, of which Adaptation and Response in Drylands (ARID) was one of two scoping studies selected. With the goal of gathering input from the scientific and data end-user communities, we provide an overview of our ARID kick-off meeting with over 300 in-person and virtual participants held in October 2023 at the University of Arizona. This meeting gathered insights from public and private data end-users and scientists. We also report on follow-up activities that have taken place since then, including town halls, community surveys, and international engagements.

Drylands occupy ~40% of the land surface and are thought to dominate global carbon (C) cycle inter-annual variability (IAV). Therefore, it is imperative that global terrestrial biosphere models (TBMs), which form the land component of IPCC earth system models, are able to accurately simulate dryland vegetation and biogeochemical processes. However, compared to more mesic ecosystems, TBMs have not been widely tested or optimized using in situ dryland CO2 fluxes. Here, we address this gap using a Bayesian data assimilation system and 89 site-years of daily net ecosystem exchange (NEE) data from 12 southwest US Ameriflux sites to optimize the C cycle parameters of the ORCHIDEE TBM. The sites span high elevation forest ecosystems, which are a mean sink of C, and low elevation shrub and grass ecosystems that are either a mean C sink or “pivot” between an annual C sink and source. We find that using the default (prior) model parameters drastically underestimates both the mean annual NEE at the forested mean C sink sites and the NEE IAV across all sites. Our analysis demonstrated that optimizing phenology parameters are particularly useful in improving the model’s ability to capture both the magnitude and sign of the NEE IAV. At the forest sites, optimizing C allocation, respiration, and biomass and soil C turnover parameters reduces the underestimate in simulated mean annual NEE. Our study demonstrates that all TBMs need to be calibrated for dryland ecosystems before they are used to determine dryland contributions to global C cycle variability and long-term carbon-climate feedbacks.