With warming, spring streamflow peaks are more coupled with vegetation green‐up than snowmelt in the northeastern United States

Abstract

In forested watersheds, climate change may have substantial implications for both ecological and hydrological processes by altering the snow and vegetation seasonal dynamics. However, to date, there have been few studies which systematically analysed their combined effects on seasonal streamflow behaviour at the watershed scale. Using long‐term remote‐sensed vegetation data and snowpack measurements, we characterized the long‐term patterns in the timings of green‐up/senescence and subsequent growing season length, as well as snowpack development/disappearance and subsequent snowpack duration. We further investigated the correlations of phenological and snowpack seasonal variations with the cumulative percentiles of daily streamflow over two transition periods: vernal (between snowmelt and green‐up) and autumnal (between senescence and snowpack development) windows. We found growing season significantly lengthened by ~30 days over the last four decades at the study watershed, driven by both earlier green‐up and later senescence. The long‐term snowfall significantly decreased by ~2.4 cm, and the snowpack duration has been shortened by ~25 days, mostly driven by earlier snow disappearance. While there were no significant changes in the lengths of vernal and autumnal windows, the normalized streamflow distributions over the vernal window have widened and the low‐frequency peak flow over the autumnal window has shifted earlier over the study period. Interestingly, although the snow disappearance timing has advanced by ~18 days, there was no evidence of changes in the timing of spring peak discharge. Our results suggest that with long‐term decreases in winter snowfall and snowpack duration, the impacts of snowpack dynamics on seasonal streamflow regimes over the vernal and autumnal windows have weakened. Meanwhile, the seasonal streamflow dynamics are more closely mediated by vegetation green‐up with time. This study emphasizes the importance of understanding the phenological responses to climate change for prediction of future seasonal flow regimes in forested watersheds.

Hydrologic implications of projected changes in rain-on-snow melt for Great Lakes Basin watersheds

“…Also, following a 2 °C warming scenario, prior research has found that the frequency of ROS melt events are expected to become approximately one month earlier in the eastern United States as cold-season snowfall switches to rainfall (Li et al, 2019), which aligns with our findings for the earlier center of volume for ROS melt over the water year. As the contributions of snowmelt to peak spring water yields become weaker due to the earlier timing of ROS events, vegetation green-up can have a more dominant influence on spring hydrographs in a changing climate (Khodaee et al, 2022).…”

Towards Forecasting Future Snow Cover Dynamics in the European Alps—The Potential of Long Optical Remote-Sensing Time Series

“…Moreover, snow strongly influences habitats and thus ensures biodiversity. Snow cover duration, for example, proves to be a strong predictor for spatial species distribution [6], while the timing of snowmelt influences plant phenology and productivity [7,8]; thus, climate-change-induced snow cover dynamics also result in habitat shifts and, again, temperature rise due to increased greening effects [4,5]. At the same time, mountains are often described as the water towers of the world, and high-altitude snow cover is a major source of freshwater for billions of people, enabling agriculture and electricity generation [9].…”

Greenup Variability Impact on Seasonal Streamflow and Soil Moisture Dynamics in Humid, Temperate Forests

“…Recently, Denham et al ( 2023) also showed that early greenup at deciduous forests led to high spring evapotranspiration (ET) to potential ET ratios from the flux tower data across the eastern US. These changes in canopy conductance and evapotranspiration (ET) during phenological transition periods (greenup and senescence) significantly affect surface soil moisture and catchment rainfall-runoff dynamics (Lian et al, 2020;Khodaee et al, 2021).Many catchment studies reported nonlinear threshold behavior of stormflow generation by combined effect of gross precipitation and antecedent soil moisture conditions, which demonstrates subsurface storage controls on rainfall-runoff dynamics at the catchment scale (e.g., Detty & McGuire, 2010;Tromp-van Meerveld & McDonnell, 2006). However, recent studies in the eastern United States reported that this strong antecedent soil moisture control on stormflow generation was moderated by canopy conductance and transpiration capacity in forest headwater catchments.…”

“…Recently, Denham et al ( 2023) also showed that early greenup at deciduous forests led to high spring evapotranspiration (ET) to potential ET ratios from the flux tower data across the eastern US. These changes in canopy conductance and evapotranspiration (ET) during phenological transition periods (greenup and senescence) significantly affect surface soil moisture and catchment rainfall-runoff dynamics (Lian et al, 2020;Khodaee et al, 2021).…”

“…Creed et al (2015) also reported that the timing of the Budyko evaporative index (the ratio of precipitation-runoff difference over precipitation) has shifted to earlier in spring and later in autumn due to lengthened growing season in temperate forest catchments in Canada. In our previous studies (Hwang et al, 2014;Hwang et al, 2018;Khodaee et al, 2021), we also examined the apparent correlations between phenology and rainfall-runoff dynamics across the eastern US where we showed that non-stationary behavior in precipitation and runoff deficit was significantly correlated with long-term and interannual variations in growing season length and subsequent vegetation growth. We also separated the net effect of lengthened growing season on water yield with a distributed ecohydrological modeling framework (Hwang et al, 2018;Kim et al, 2018).…”