Multi-source comparison of recent terrestrial evapotranspiration trends: Introducing a topology framework.

Evapotranspiration (ET) plays a central role in the terrestrial water cycle by coupling water, energy, and carbon exchanges between land and atmosphere. A Recent intercomparison of global ET products (Thomson and Markonis, 2024) revealed substantial uncertainties in estimated ET trends, including strong product dependence in magnitude, spatial patterns, statistical significance, and even trend direction.

Here, we extend this work by introducing a topology framework that categorizes ET products based on their trend signatures. We processed and harmonized 14 global ET products—derived from reanalysis, remote sensing, synthesis approaches, and land surface models—onto a common 0.25° × 0.25° grid for the period 2000–2019. ET trends and associated significance were estimated using a block-bootstrapped Theil–Sen estimator at the grid scale and across meaningful spatial groupings, including IPCC reference regions, biomes, land-cover classes, Köppen–Geiger climate zones, elevation classes, and evaporation quantiles.

Using this catalogue of recent ET trends and trend indices, such as the dataset concurrence index (DCI), we construct product-specific topologies by ranking the area fraction associated with characteristic behaviors including positive and negative signal boosters, and several forms of opposition.

Globally, we find that “top negative signal boosters” are also “top outliers”. This means that top outliers are products that produce significant negative trends where all other significant trends are positive. This is caused by a majority of products producing positive trends. However, “top positive signal boosters” tend to be “top signal opposers”. These products have significant positive trends where the majority of products have nonsignificant trends. Both tendencies are true for a range of p-value thresholds. As a result, apparent large-scale ET trend signals are often driven by a limited number of products rather than by broad inter-product agreement.

These topologies transform complex multi-product trend information into intuitive categories, enabling systematic identification of product-specific uncertainties and agreement patterns in large-scale ET trend assessments. This framework provides a new basis for categorizing ET products supporting interpretation of large-scale ET changes and data selection.

Thomson, J. and Markonis, Y.: Multi-source analysis of recent changes in global terrestrial evapotranspiration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-917, https://doi.org/10.5194/egusphere-egu24-917, 2024.