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Budget analyses are useful indicators of sub-regional dynamics.
Hydrologic budgets are one of the tools used to verify that the ELM hydrology
is comparable to that of the SFWMM.
The ELM and SFWMM Annual water budgets
provide a spatially and temporally aggregated tool to evaluate all of the
inflows and outflows from the hydrologic basins
that are summarized by both models. The flow volumes are all expressed as the height (cm)
of the volume if it were distributed across a basin, calculating mean monthly sums for each year
of simulation.
There are several issues that need consideration while viewing these budget comparisons:
The ELM writes data to budget files at recurring 30 julian-day intervals, while the SFWMM uses a calendar basis for creating monthly budgets. Thus, the ELM mean values during each year use beginning and ending date points that are not exactly on Jan 1 and Dec 31, and the number of "monthly", or 30-day, data points in calculating annual mean flows is not always 12 as the julian and date calendars are not coincident. (The ELM writes the exact calendar date for all data points, but it does not use a calendar basis for determining data output intervals).
The scale of the two models is different (1.0 km^2 vs. 10.4 km^2), and thus the basin sizes are not the same in the two grid-based representations. The budget data are expressed in water flow volumes in the respective (SFWMM or ELM) basin. In order to directly compare the two models, the SFWMM vertical flows (rain and ET) were normalized to the basin size of the ELM, thus facilitating between-model comparisons in those cases where the basin domains are different.
WCA3A&B sums of levee+groundwater in&out flows.
