Recent Patterns in Climate, Vegetation, and Forest Water Use in California Montane Watersheds

Abstract

California has recently experienced one of the worst droughts on record, negatively impacting forest ecosystems across the state. As a major source of the region's water supply, it is important to evaluate the vegetation and water balance response of these montane forested watersheds to climate variability across the range of rain-to snow-dominated precipitation regimes. The Standardized Precipitation Index (SPI) and the Standardized Runoff Index (SRI) were used to capture the hydrologic drought signal, and MODIS vegetation indices (i.e., the normalized difference vegetation index and the enhanced vegetation index) were used to evaluate the vegetation and evapotranspiration response in three headwater catchments. The study catchments comprised a low elevation rain-dominated site (Caspar Creek) on the northern California coast, a mid-elevation site with a mix of rain and snow (Providence Creek) in the California Sierra Nevada, and a high elevation snow-dominated site (Bull Creek) in the Sierra Nevada. Lowest SPI values occurred in the third drought year of 2014 for all sites. Lowest SRI was in 2014 for Caspar, but in 2015 for Providence and Bull, reflecting differences in snowpack-delayed runoff and subsurface storage capacity between the lower and higher elevation watersheds. The most accurate water balance closure using evapotranspiration estimates from vegetation indices was within 10% of measured precipitation at snow-dominated Bull. The rain-dominated Caspar watershed had the highest vegetation index values and annual evapotranspiration, with the lowest variability over the previous 13 years (2004-2016). Vegetation index values and annual evapotranspiration decreased with increasing elevation and snow contribution to precipitation. Both snow-influenced Sierra Nevada watersheds showed elevated vegetation and evapotranspiration responses to interannual climate variability. There remains a need for institutional support to expand long-term observations in remote forested mountain watersheds to monitor and research these changing and extreme environmental conditions in source watershed regions.

How realistic are water‐balance closure assumptions? A demonstration from the southern sierra critical zone observatory and kings river experimental watersheds

“…We have utilized a rich dataset from the SSCZO and KREW to test water-balance closure assumptions and errors at various spatial and temporal scales. Our water-balance closure errors (i.e., G n and Δ) were within the range of values reported in earlier studies (Bales et al, 2018;Gao et al, 2010;Saksa et al, 2017;Wang et al, 2015;Wang, Huang, et al, 2014; (Abera et al, 2017;Engeland et al, 2005;Tardif et al, 2015;, our results show that a high proportion of the closure error term can be attributed to the magnitude of P and Q (Figure 6).…”

“…We have utilized a rich dataset from the SSCZO and KREW to test water‐balance closure assumptions and errors at various spatial and temporal scales. Our water‐balance closure errors (i.e., and ∆) were within the range of values reported in earlier studies (Bales et al, 2018; Gao et al, 2010; Saksa et al, 2017; Wang et al, 2015; Wang, Huang, et al, 2014; Wang, McKenney, et al, 2014). Gao et al (2010) reported a 20% water‐balance closure error using remotely sensed P , ET and dS / dt for the combined San Joaquin and Sacramento River basins.…”

Snowfall interception in a deciduousNothofagusforest and implications for spatial snowpack distribution

“…Due to their hydrological and ecological implications, snow–forest interactions have been intensely studied in cold regions of the world, particularly in the Northern Hemisphere; there, forests cover vast expanses of snow‐dominated landscape. Snow processes and their relationship with the forest determine the availability of water on the surface and the snow melt rates, influencing aquifer recharge processes, evapotranspiration of vegetation, and water supply in the basin in periods of melting (Hedstrom & Pomeroy, ; Moeser et al, ; Pomeroy, Parviainen, Hedstrom, & Gray, ; Rasmus, Lundell, & Saarinen, ; Saksa, Safeeq, & Dymond, ).…”

“…forest determine the availability of water on the surface and the snow melt rates, influencing aquifer recharge processes, evapotranspiration of vegetation, and water supply in the basin in periods of melting Moeser et al, 2016;Pomeroy, Parviainen, Hedstrom, & Gray, 1998;Rasmus, Lundell, & Saarinen, 2011;Saksa, Safeeq, & Dymond, 2017).…”

Spatially distributed water-balance and meteorological data from the rain–snow transition, southern Sierra Nevada, California

“…Major SSCZO research questions focus on the links between climate, regolith properties, vegetation, biogeochemistry, hydrology, and the response of the mountain ecosystem and catchments to disturbance and climate change. Related studies include evaluation of the transect of eddy covariance and evapotranspiration (Goulden et al, 2012;Goulden and Bales 2014;Saksa et al, 2017;Bales et al, 2018), soil moisture (Oroza et al, 2018), hydrologic modeling (Tague and Peng, 2013;Bart et al, 2016;Son et al, 2016;Bart and Tague, 2017;Jepsen et al, 2016), biochemical studies (Liu et al, 2012;Carey et al, 2016;Aciego et al, 2017;Arvin et al, 2017;Hunsaker and Johnson, 2017), geophysical research (Hahm et al, 2014;Holbrook et al, 2014), and sediment composition (Stacy et al, 2015;McCorkle et al, 2016). Regolith water storage is further described in Klos et al (2018).…”