Observations of precipitation isotopes are used to determine the spatial and temporal performance of modeled precipitation recycling in the tropics
The variability in precipitation recycling ratios has important implications for the availability of water to plants as well as tracking the movement of water through the water cycle. Field-based measurements of precipitation recycling over large areas are lacking due to the challenges associated with distributing the necessary equipment. As such, scientists have relied more on modeled precipitation recycling estimates over large scales, while precipitation isotopes have been used as a proxy at the local scale. By aggregating these isotopic observations through space and time, we were able to provide the first global-scale assessment of modeled precipitation recycling estimates using observations over the humid tropics region.
The quantity of precipitation recycling represents the amount of precipitation made available to a given area by plants. Heavily forested areas like the Amazon rainforest are known to derive anywhere from one third to one half of its water from precipitation recycling. As such, changes in this quantity are important to understand, as they may provide a direct indication of the health and sustainability of plant ecosystems. Our approach can be used to check how models are doing so modifications to the models can be made to improve performance. Such efforts will be critical to understand how plants and the water cycle will be impacted by climate change at local to regional scales.
The amount of precipitable water derived locally through transpiration from plants is known as precipitation recycling. By transpiring water that recently fell as rain, plants are effectively recycling water back to the atmosphere so it can fall as rain again. A multi-international team of scientists covering both modelers and experimentalists developed a new approach that uses observed isotopes in precipitation record (a known proxy of precipitation recycling) to constrain estimates from models, which had largely been used to evaluate these quantities over larger scales. Two types of models were assessed in this study – the mass balance and particle tracking models – the latter of which were only made possible very recently through advancements in computational power that were required to perform such simulations. This research highlights which of these models tend to perform better over different times of year based on comparisons to the isotopic observations. In addition, the models were assessed over different regions of the tropics that were broken down by climate zone to see how these might be playing a role in performance based on the physics of the model. Our new approach can be used to improve future modeled estimates of precipitation recycling so that we may better understand its variability and potential impact on plants in response to climate change.
Kurt Solander, Los Alamos National Laboratory, firstname.lastname@example.org
This research was supported as part of the Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics) funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research.
Cropper, S., Solander, K., Newman, B.D. et al. “Comparing deuterium excess to large-scale precipitation recycling models in the tropics.” npj Climate and Atmospheric Science 4, 60 (2021). https://doi.org/10.1038/s41612-021-00217-3