A multisector analysis of urban irrigation and water savings potential

Abstract:

Urban irrigation strains limited water supplies in semi-arid areas such
as Orange County, CA, yet the quantity and controlling factors of urban
irrigation are not well understood. The goals of this research are to
(1) quantify and compare landscape irrigation applied by residential and
commercial sectors in various retail agencies at a parcel scale (2)
determine over- and under-irrigation compared to theoretical need (3)
determine the climatic and socioeconomic controls on landscape
irrigation. A research partnership was established between six water
retail agencies in Orange County, CA representing a wide range of
climatic and economic conditions. These agencies contributed between 3
and 13 years of water use data on a monthly/bimonthly basis. Irrigation
depth (mm) was estimated using the "minimum month method," and landscape
evapotranspiration was calculated using the Hargreaves equation for
122,345 parcels. Multiple regressions of water use were conducted with
climatic and socioeconomic variables as possible explanatory variables.
Single family residences accounted for the majority of urban water use.
Findings from 112,192 single family residences (SFRs) show that total
and indoor water use declined, though irrigation did not significantly
change. Average irrigation for SFRs was 94 L/day, and a large proportion
(42%) of irrigation was applied in excess to landscapes. Air temperature
was found to be the primary driver of irrigation. We mapped
over-irrigation relative to plant water demand to highlight areas that
can be targeted for water conservation efforts. We also show the water
savings that would be gained by improving the efficiency of irrigation
systems. The information gained in this study would be useful for
developing water use efficiency policies and/or educational programs to
promote sustainable irrigation practices at the individual parcel scale.