Observed changes in hydroclimate attributed to human forcing

Abstract

Observational and modeling studies indicate significant changes in the global hydroclimate in the twentieth and early twenty-first centuries due to anthropogenic climate change. In this review, we analyze the recent literature on the observed changes in hydroclimate attributable to anthropogenic forcing, the physical and biological mechanisms underlying those changes, and the advantages and limitations of current detection and attribution methods. Changes in the magnitude and spatial patterns of precipitation minus evaporation (P–E) are consistent with increased water vapor content driven by higher temperatures. While thermodynamics explains most of the observed changes, the contribution of dynamics is not yet well constrained, especially at regional and local scales, due to limitations in observations and climate models. Anthropogenic climate change has also increased the severity and likelihood of contemporaneous droughts in southwestern North America, southwestern South America, the Mediterranean, and the Caribbean. An increased frequency of extreme precipitation events and shifts in phenology has also been attributed to anthropogenic climate change. While considerable uncertainties persist on the role of plant physiology in modulating hydroclimate and vice versa, emerging evidence indicates that increased canopy water demand and longer growing seasons negate the water-saving effects from increased water-use efficiency.

Evaluation of hydroclimatic biases in the Community Earth System Model (CESM1) within the Mississippi River basin

“…Ongoing and projected changes in streamflow due to climate change remain uncertain because of the complex and dynamic nature of river systems and the interactions between the ocean, atmosphere, and land surface that govern terrestrial hydrologic 25 processes (Clark et al, 2015;Fisher & Koven, 2020;Good et al, 2015;Wood et al, 2011). Our understanding of hydrologic changes is informed by observational datasets, but earth system and hydrologic models play an increasingly critical role in examining the impacts of climate variability and climate change on river discharge as systems vary outside of what has previously been observed as normal (Fowler et al, 2022;Herrera et al, 2023;Milly et al, 2008). However, several key hydrologic processes that regulate river discharge remain poorly constrained in earth system models.…”