Observing hydroclimatic variability during the 2012-2015 drought using a Great Basin mountain transect: elevation matters!

Hydroclimate in the semi-arid Great Basin region of the western U.S. is highly variable on an interannual basis, and annual water budgets of valleys containing large groundwater reserves are loosely estimated because of a general lack of observational data in the nearby mountains. Elevation gradients along mountain ranges experience dramatic differences in seasonal water balance due to topographic mechanisms (e.g., orographic precipitation enhancement, snow retention, and reduced vapor pressure deficit). Individual storms and other short-term regional circulation events are important at the local scale in this region as well. How ecological communities respond to this high variability and whether it is reflected in mountain-block groundwater recharge remain open questions. To demonstrate the value of instrumenting mountain gradients to provide a more quantitative assessment of the annual water cycle, we present detailed data available during the four recent drought years (2012-2015) from automated sensor installations within the Nevada Climate-ecohydrological Assessment Network (NevCAN). Crucially, monthly percentages of precipitation falling as snow were consistent across all years at upper elevations, but varied from year-to-year at lower elevations. Precipitation intensity and amount varied significantly with elevation during cold seasons, but was surprisingly uniform during warmer seasons. Duration of peak soil dryness in the summertime decreased with elevation, showing the capability of mountains to buffer drought. Two separate seasonal patterns of precipitation were observed during these "low snow" years: one with dry springtime and wet summers, followed by the reverse of this seasonality. Gradient data on seasonal precipitation amount, phase, and intensity, as well as snow presence, shallow soil moisture, and vegetation response, are crucial to improving ecological and hydrological investigations across both mountains and valleys in this historically data-poor region.