Reply on RC2

Benjamin Hatchett

doi:10.5194/nhess-2021-193-ac2

Abstract

Snow droughts are commonly defined as below average snowpack at a point in time, typically 1 April in the western United States (wUS). This definition is valuable for interpreting the state of the snowpack but obscures the temporal evolution of snow drought. Borrowing from dynamical systems theory, we applied phase diagrams to visually examine the evolution of snow water equivalent (SWE) and accumulated precipitation conditions in maritime, intermountain, and continental snow climates in the wUS using station observations as well as spatially distributed estimates of SWE and precipitation. Using a percentile-based drought definition phase diagrams of daily observed SWE and precipitation highlighted decision-relevant aspects of snow drought such as onset, evolution, and termination. The phase diagram approach can be used in tandem with spatially distributed estimates of daily SWE and precipitation to reveal variability in snow drought type and extent. When combined streamflow or other data, phase diagrams and spatial estimates of snow drought conditions can help inform drought monitoring and early warning and help link snow drought type and evolution impacts on ecosystems, water resources, and recreation. A web tool is introduced allowing users to create real-time or historic snow drought phase diagrams.

Highlights

Snow-dominated mountains provide critical water resources to ecosystems and society (Viviroli et al, 2007; Sturm et al, 2017; Immerzeel et al, 2020), but their snowpacks are susceptible to climate warming (Beniston, 2003; Pepin et al, 2015; 15 Rhoades et al, 2018c; Siirila-Woodburn et al, 2021)
Our primary goal was to demonstrate a visualization approach to show the temporal evolution of snow drought conditions, and more broadly mountain hydroclimatic conditions, through the cool season
We provided examples showing a range of applications in various snow climates for extreme years and how additional data such as spatially distributed snow water equivalent (SWE) and precipitation as well as river discharge can further enhance the utility of information provided by phase diagrams

Summary

Introduction

Snow-dominated mountains provide critical water resources to ecosystems and society (Viviroli et al, 2007; Sturm et al, 2017; Immerzeel et al, 2020), but their snowpacks are susceptible to climate warming (Beniston, 2003; Pepin et al, 2015; 15 Rhoades et al, 2018c; Siirila-Woodburn et al, 2021). Warming impacts mountain regions in many ways, including reductions in the amount of water stored in snowpack (Mote et al, 2018), earlier spring snowmelt (Kapnick and Hall, 2012; Musselman et al, 2021), and slower snowmelt (Musselman et al, 2017). As rain falls instead of snow, runoff becomes less efficient (Berghuijs et al, 2014), a process amplified by increasing atmospheric demand 20 for moisture (Fisher et al, 2017). Spring snowpack is an important predictor of warm season runoff for environmental flows and human consumptive use.

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