sac_year_type_calc: Compute Sacramento Valley Water Year Index for CRSS

In BoulderCodeHub/CRSSIO: Package to Manage the Input and Output of CRSS Data

Compute Sacramento Valley Water Year Index for CRSS

Description

sac_year_type_calc() calculates the Sacramento Valley Water Year (WY) Index using either the Sacramento 4 river index water year volume, or Colorado River WY intervening natural flow data. Note that these methods are implemented only for purposes of generating an index to use in CRSS.

Usage

sac_year_type_calc(wy_vol = NULL, co_int_nf = NULL)

Arguments

wy_vol	xts object containing Sacramento 4-river index water year volumes in million acre-feet. xts object must have yearly periodicity.
co_int_nf	nfd object that has annual, intervening data and has the "wy" year type. It also must have 29 sites that are named the same as the expected site names in a crss_nf object.

Details

CRSS uses the Sacramento Valley Water Year Index to determine MWD's desired annual ICS activity. This method adds plausible variability to the CRSS projections based on MWD’s needs for storage or delivery of Colorado River water based on the availability of their other California supplies. The index is available for 1906-present (see sac_year_type_get()), which is used for hydrology scenarios that rely on historical data. For other scenarios, e.g., paleo, or statistical generated, the index must be calculated from other available data.

If the Sacramento 4 river index water year (WY) volume is available (like it is going back to 900 C.E. based on paleo reconstructions), the WY volume can be used to recreate the index values. In this case, the following formula is used, which is derived from the official formula documented at http://cdec.water.ca.gov/cgi-progs/iodir/WSIHIST.

index_t = 0.323 * RWY + 0.3 * min(index_{t-1}, 10.0)

where RWY is the Sacramento 4 river WY volume in million acre-feet. Note that because the index in the first year depends on the index value from the previous year, which is unknown, the 0th index value is assumed to be an average year with an index value of 7.8.

When the Sacramento 4 river index WY volume is unknown, the index can be generated from the Colorado River natural flow data since these must always be available for use in CRSS. The index is created based on a decision tree that is fit to the water year intervening natural flow for all 29 sites in the Colorado River Basin. See XXXX for details on the development and tuning of this decision tree.

Value

xts object. When using wy_vol will have the same number of columns as wy_vol. When using co_int_nf will have the same number of columns as there are traces in co_int_nf.

BoulderCodeHub/CRSSIO documentation built on July 2, 2023, 5:15 p.m.