Moisture Budgets and Circulation Analogs: Diagnosing Dynamic and Thermodynamic Precipitation Change

TL;DR

This study compares two methods for separating dynamic and thermodynamic contributions to precipitation trends, applying them to climate model data and reanalyses to improve regional climate change understanding.

Contribution

It introduces a combined framework using moisture budgets and circulation analogs to better distinguish precipitation change drivers and refine future projections.

Findings

Dynamic trend estimates often differ between methods for individual ensemble members.

Ensemble mean trends agree in sign but differ in magnitude.

The combined approach yields weaker thermodynamic precipitation change projections.

Abstract

Precipitation trends can arise from both dynamic factors (changes in atmospheric circulation) and thermodynamic factors (changes in atmospheric moisture content). Disentangling these contributions can aid in understanding regional climate change and improving projections. We compare two approaches which separate dynamic and thermodynamic contributions to precipitation trends over Central Chile: a moisture budget analysis and constructed circulation analogs. Both methods are applied to fields from the CESM2 Large Ensemble as well as two reanalyses. We analyze the methodological differences that lead to distinct results in each approach and evaluate their respective capabilities in capturing dynamic, thermodynamic and coupled trends. We find that the estimated dynamic trends from both methods often differ substantially for individual ensemble members, although the ensemble mean generally agrees in sign but not in magnitude. Finally, we apply circulation analogs to moisture budget terms to refine estimates of historical and future precipitation change in Central Chile. This combined framework reduces dynamic contamination of thermodynamic trends and yields projections of thermodynamic precipitation change that are weaker than that suggested by either method alone.