Soil moisture datasets at five sites in the central Sierra Nevada and northern Coast Ranges, California

Science Center Objects

Soil moisture is a critical variable for understanding the impacts of drought on ecological, hydrological, and agricultural systems, as soil moisture content has a direct affect on runoff amounts. Runoff occurs as the result of precipitation (both rainfall and snowfall) that is in excess of the demands of evaporation from land surfaces, transpiration from vegetation, and infiltration into soils. The water that remains available, or runoff, is the amount of water that makes its way to streams, rivers, and, possibly, to the ocean. In situ soil moisture datasets are also important inputs used to calibrate and validate watershed, regional, or statewide modeled and satellite-based soil moisture estimates.

Soil moisture and temperature data were collected from five study sites, three in the central Sierra Nevada Range (Yosemite National Park), and two in the northern Coastal Range (Pepperwood Preserve). The two study areas represent geologic and hydroclimatic contrasts that were selected for the purpose of understanding hydrologic, climatic, and biologic soil moisture dynamics in snow-dominated watersheds and coastal fog-dominated watersheds. The Yosemite National Park sites in the Sierra Nevada had soil moisture and temperature sensors installed to study the influence of elevation changes and snow pack on soil properties in the central Sierra Nevada. The Pepperwood Preserve monitoring sites in the northern Coast Ranges had soil moisture and temperature sensors installed to study the interaction of rain, moisture from fog, general weather conditions, and the effect that grassland and oak woodland environments can have on soil conditions and biodiversity.

This dataset will contribute long-term hourly time-series of soil temperature, volumetric water content, water potential, and total soil water content data to the public domain to help improve the understanding of the soil's response to climate.

 

Soil moisture snow-dominated data collection sites within Yosemite NP

Location of three snow-dominated data collection sites within the Yosemite National Park: Dana Meadows, Gin Flat, and Hodgdon Meadow. (Public domain.)

Snow-Dominated

The Yosemite National Park sites had soil moisture and temperature sensors installed to study the influence of elevation changes and snow pack on soil properties in the central Sierra Nevada Range. Three monitoring sites (Dana Meadows, Gin Flat, and Hodgdon Meadow) were set up in Yosemite National Park, on the western slope of the central Sierra Nevada Range.

 

Yosemite National Park is characterized by a Mediterranean climate with hot, dry summers and cool, wet winters. Most of the precipitation in higher elevations falls as snow (Klinger and others, 2006). Mean annual precipitation ranges from 900 millimeters (mm) at lower elevations to 1,200 mm at higher elevations (Klinger and others, 2006). Snow water equivalent in the snowpack has been estimated to be greater than 700 mm (Bales and others, 2006). Mean daily summer temperatures range from 33 degrees Celsius (°C) in the lower elevations to 12 °C in the higher elevations (Klinger and others, 2006). Mean daily winter temperatures range from 8 to −4 °C in the lower and higher elevations, respectively (Klinger and others, 2006).

 

 

 

 

Map of soil moisture fog dominated watershed sites

Location of two fog-dominated data collection sites within Pepperwood Preserve: Grass and Oak. (Public domain.)

 

 

Fog-Dominated

Two monitoring sites were set up at the Pepperwood Preserve, a 12.6 km2 nature preserve in Sonoma County, about 20 km northeast of the city of Santa Rosa. The Pepperwood Preserve was established in 1979 to protect native coastal grassland and oak woodland habitats (de Nevers, 2013). The climate surrounding the Pepperwood Preserve is classified as Mediterranean with cool, moist winters and warm, dry summers (de Nevers, 2013). Unique to the northern California coast is the presence of fog throughout the year. This fog presence reduces temperatures and increases humidity along the coast.

The Pepperwood Preserve monitoring sites had soil moisture and temperature sensors installed to study the interaction of rain, moisture from fog, general weather conditions, and the effect that grassland and oak woodland environments can have on soil conditions and biodiversity.

 

 

 

 

 

 

 

 

 

Measuring Soil Moisture

Heat dissipation probes, time domain reflectometry probes, and ECH2O EC-TM probes were used to collect soil moisture and temperature data. Data loggers and telemetric equipment were used for the collection, storage, and transfer of data. A tipping bucket was installed to collect precipitation data for the Pepperwood Preserve sites. The Yosemite National Park sites require a visit to each site to download data from the data loggers, whereas Pepperwood Preserve sites have telemetric equipment to download data remotely.

 

Heat Dissipation Probe (HDP)

Heat dissipation probes are used to determine water potential at specific soil depths. Heat dissipation (also called thermal diffusivity) is an indirect method of measuring soil water matric potential. 

Heat Dissipation Probe (HDP)

Heat dissipation probes were deployed at each of the five soil moisture monitoring sites to determine water potential at specific soil depths. Heat dissipation (also called thermal diffusivity) is an indirect method of measuring soil water matric potential. A heating element is encased in a ceramic body with a thermocouple at midlength. When the HDP is installed, water potential changes in the surrounding soils create a water flux with the ceramic matrix in equilibrium. The heating element initiates a heat pulse, and the temperature after 20 seconds (delta T) is measured. The delta T is dependent on the thermal properties of the ceramic (including water content) and can thus be calibrated and used to compute soil water matric potential.

 

ECH2O EC-TM Soil Moisture Probes

ECH2O EC-TM probes, designed to measure water content and temperature. measure soil water content indirectly and use an electromagnetic field to measure the dielectric permittivity of the surrounding material.

 

 

ECH2O EC-TM Soil Moisture Probes

ECH2O EC-TM probes, used at all five sites, are designed to measure water content and temperature. measure soil water content indirectly and use an electromagnetic field to measure the dielectric permittivity of the surrounding material. The probe supplies a 70 megahertz (MHz) oscillating wave to the three probe prongs that are sensitive to the dielectric permittivity of the surrounding material. The stored charge is proportional to soil dielectric and soil VWC. The internal microprocessor measures the stored charge and outputs a value from the probe.

 

Time Domain Reflectometry (TDR)

Time domain reflectometry probes are used to determine volumetric water content (VWC) at specific soil depths.

 

 

 

 

 

 

 

 

 

Time Domain Reflectometry (TDR)

Time domain reflectometry probes were used at each of the five sites to determine volumetric water content (VWC) at specific soil depths. The TDR probes use an indirect method to measure soil water content. They contain stainless steel rods that are sensitive to the dielectric permittivity of the surrounding material. The TDR output wave is converted to VWC using a calibration equation and lab VWC measurements.

 

Tipping Bucket

The tipping bucket rain gage funnels precipitation into a bucket mechanism that tips when filled to a predetermined calibrated level.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tipping Bucket Rain Gage

A tipping bucket rain gage was installed at the Pepperwood Preserve Grass site to measure precipitation. The rain gage funnels precipitation into a bucket mechanism that tips when filled to a predetermined calibrated level. A magnet attached to the tipping mechanism triggers a switch as the bucket tips. The switch closure is recorded by the pulse-counting circuitry of the data logger.