Citation Information

Originator:  Lorraine Flint
Originator:  Alan Flint
Originator:  James Thorne
Originator:  Ryan Boynton

Publication Date:  2017

Title:  Provisional dataset: California Basin Characterization Model v8 Historical Long Term Average (1981-2010) Recharge and Runoff

Data Presentation Form:  ASCII grid file (.asc)

Publication Information:  
Publication Place:  Reston, VA
Publisher:  U.S. Geological Survey

Online Linkage:  https://dx.doi.org/10.1186/2192-1709-2-25

Larger Work Citation:  

Citation Information

Abstract

The California Basin Characterization Model (CA-BCM 2014) dataset provides historical and projected climate and hydrologic surfaces for the region that encompasses the state of California and all the streams that flow into it (California hydrologic region). The CA-BCM 2014 applies a monthly regional water-balance model to simulate hydrologic responses to climate at the spatial resolution of a 270-m grid. The historical data is based on 800m PRISM data spatially downscaled to 270 m using the gradient-inverse distance squared approach (GIDS). The BCM approach uses a regional water balance model based on this high resolution precipitation and temperature as well as elevation, geology, and soils to produce surfaces for the following variables: precipitation, air temperature, April 1st snowpack, recharge, runoff, potential evapotranspiration (PET), actual evapotranspiration, and climatic water deficit, a parameter that is calculated as PET minus actual evapotranspiration. Data variables included in this release: Recharge - Amount of water that penetrates below the root zone, mm (rch) and Runoff - Amount of water that becomes stream flow, mm (run). Model inputs include: precipitation, air temperature, and potential evapotranspiration. Model outputs are: actual evapotranspiration, climatic water deficit, April snow pack, recharge and runoff. These provisional results include estimates of natural recharge and runoff as a 30-year mean (1981-2010).

The provisional BCMv8 is a refined version of the Basin Characterization Model (v65, Flint and others, 2013; Flint and Flint, 2014). It has been revised to include 7 new features;

1. monthly vegetation-specific actual evapotranspiration for 65 vegetation types,
2. spatially distributed calibration coefficients for snow accumulation and snowmelt,
3. mapped soil organic matter,
4. soil hydraulic properties calculated from soil texture and soil organic matter (model runs done with water content at field capacity of -0.01 MPa and wilting point of -6 MPa),
5. soil dry out below wilting point at a rate driven by average statewide aridity,
6. a switch allowing for the incorporation of urban impermeable surfaces, and
7. internally calculated gaining and losing streams.

Rigorous calibrations have been performed statewide to improve the accuracy of all components of the water balance. Precipitation, snow processes, and the energy balance are developed and calibrated statewide. Calibrations are done to constrain the other variables, AET as a function of available soil water and vegetation type, recharge versus runoff as a function of soil storage and bedrock permeability. Calibration exercises have been done using a series of approaches to develop confidence in the regional estimates. Regional calibration means that errors are minimized statewide, and because they rely on bedrock types and vegetation types that may span across very large areas, errors may be positive or negative in different watersheds. Baseflow separation analyses at 160 streamgages, 20 basins for which recharge is estimated for groundwater flow modeling, gridded actual evapotranspiration estimates for 2000-2013 for 65 vegetation types, estimates of full natural flows from DWR (CDEC) for basins draining into the Central Valley, and 65 small basins with relatively unimpaired streamflow gages. Because of the regional calibration and associated errors, additional local calibration may be necessary to get the highest accuracy estimates for calculating the water budget in a given watershed. Model results are “unimpaired”, meaning they represent natural hydrologic conditions where water is not extracted from or delivered to a basin. Locations with mapped irrigated agriculture assume no irrigation and are treated as annual grasslands, and mapped urban footprints (from 2014 vegetation map) assume impermeable surfaces are represented by a bedrock permeability similar to granite for the whole footprint in the vegetation map, which increases runoff and decreases recharge in comparison to permeable surfaces.

Purpose

BCMv8 has been developed to improve quantitative estimates of the components of the water balance, include vegetation types, and increase ability to evaluate disturbance and management actions at local, watershed, and regional scales.