Climate Elasticity of Low Flows in the Maritime Western U.S. Mountains

Abstract

Summer streamflow is an important water resource during the dry summers in the western United States, but the sensitivity of summer minimum streamflow (low flow) to antecedent winter precipitation as compared with summer evaporative demand has not been quantified for the region. We estimate climatic elasticity of low flow (percent change in low flow divided by percent change in climatic forcing variable) with respect to annual maximum snow water equivalent (ESWE), winter precipitation (EPPT), and summer potential evapotranspiration (EPET) for 110 unmanaged headwater catchments in the maritime western U.S. mountains. We find that |EPET| is larger than |EPPT| and |ESWE| in every catchment studied and is 4–5 times larger than both, on average. Spatial variations in E are dominated by three patterns. First, |EPPT|, |ESWE|, and |EPET| are largest and most variable among semiarid catchments and decrease nonlinearly with increasing values of the humidity index (the ratio of annual precipitation to annual evaporative demand). Second, |EPPT| and |EPET| are lower in snow‐dominated catchments than in rain‐dominated catchments, suggesting that snow cover reduces the proportional response of low flows to climatic variability. Third, |EPPT|, |ESWE|, and |EPET| are lower in slow‐draining catchments than in fast‐draining catchments, for which baseflow recession storage coefficients are used to represent the rate at which catchment water storage is translated into streamflow. Our results provide the first comparison of summer low‐flow elasticity to PPT versus PET and its spatial variation in the maritime western U.S. mountains.

Evapotranspiration feedbacks shift annual precipitation-runoff relationships during multi-year droughts in a Mediterranean mixed rain-snow climate

“…Our results show that shifts in precipitation-runoff relationship may take place both in volcanic, subsurface-flow-dominated and in transitional-to-granitic, surface-runoff-dominated basins. This may seem counterintuitive as the volcanic Almanor sub-basin has a relatively small inter-annual variability in low flows that agrees with other studies in similar contexts (Jefferson et al, 2008;Tague et al, 2008;Cooper et al, 2018), and this variability is an important driver of shifts in Australian basins (Saft et al, 2016b). However, while the surface-runoff-dominated East Branch does return larger shifts both overall (M Q ) and for individual droughts (m Q , see Section 3.2), both this sub-basin and the Almanor are rain-shadowed (aridity index of ∼1.5 and 1.1, respectively).…”

“…Also, the model systematically underestimated both the absolute value and the interannual variability of changes in sub-surface storage, in particular for the Almanor sub-basin ( Figure S3) and for the Feather River at Oroville ( Figure 7); PRMS failed to reproduce the multi-decadal decline in storage observed in all (sub-)basins as a result. While the observed changes in sub-surface storage used in this paper to evaluate PRMS may suffer from unquantifiable uncertainty across precipitation, full-natural flow, and GAM-estimated evapotranspiration, this decline was confirmed by other soft data collected on the river (Freeman, 2011) and agrees with a general trend of declining summer low flows in the Maritime Western U.S. (Cooper et al, 2018).…”

“…Climate elasticity measures the sensitivity of annual streamflow (in this case, full-natural flow) to changes in a relevant climate variable, usually precipitation and potential evapotranspiration (Andréassian et al, 2016;Cooper et al, 2018). Compared to NSE and bias, contrasting observed and simulated elasticity quantifies the performance of a hydrologic model in simulating inter-annual variability in streamflow and its relation to external forcings.…”

From Drought to Flood: A Water Balance Analysis of the Tuolumne River Basin during Extreme Conditions (2015 – 2017)

“…We attribute the lower RE in 2015 to a combination of (a) increased contribution to the depleted aquifer storage from the previous few years of drought, and (b) increased ET during an extended snow‐free season. This assessment is consistent with the findings of Berghuijs et al (2014), Cooper et al (2018), and Godsey et al (2014), who showed that increases in rainfall precipitation proportions across historically snow‐dominated basins resulted in lower runoff amounts.…”

Twenty-First Century Streamflow and Climate Change in Forest Catchments of the Central Appalachian Mountains Region, US

“…The sensitivity to both P and PET increases with increasing n value since the higher value of n generally corresponds to greater E for a given P and PET (Figure 2). The n value is a function of precipitation, topography, and slope [47,65,72,73], indicating lower water availability in regions with higher n value.…”