Afternoon Slump; The role of antecedent snowpack on midday transpiration declines
Abstract
In the early afternoon, the vapor pressure deficit can cross a threshold that decouples transpiration from atmospheric evaporative demand (VPD). The factors that define this threshold and how it varies between species and in response to external factors such as soil moisture content and radiation are difficult to estimate as they reflect hydraulic traits and leaf temperature. Ultimately, the time of day and frequency that this threshold is crossed has important implications for total forest water use and how forests respond to synoptic weather and drought. Here, we present sap flux data from 7 sites in the East River Watershed, Colorado that span a 650 m altitudinal transect and includes co-located Abies lasiocarpa, Picea engelmannii and Populus tremuloides. We characterize the seasonal evolution of the structure of the diurnal cycle in sap flux and assess the threshold at which the decoupling occurs. This pattern is mapped across the transect along with an assessment of seasonal origins of plant water use from stable isotope of the xylem water. We use these data to assess the importance of antecedent snowpack in modulating decoupling between transpiration and VPD. We present preliminary data from the 2019 growing season which was associated with the largest spring snowpack in recent history establishing an end member for the effect of snowpack on summer soil moisture.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H11P1741P
- Keywords:
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- 0740 Snowmelt;
- CRYOSPHERE;
- 1621 Cryospheric change;
- GLOBAL CHANGE;
- 1813 Eco-hydrology;
- HYDROLOGY;
- 1817 Extreme events;
- HYDROLOGY