Abstract:
Accurate assessment of water budgets is critical for effective management of water resources,
especially on small, densely-populated islands with extremely limited storage capacity such as
Puerto Rico. A water budget defines a balance between inputs, outputs, and storage. The water
budgets described herein provide a generalized summary of the inputs, extractions, and outputs
from four watersheds in and near the Luquillo mountains using rainfall, runoff, and public-supply
extraction data as well as estimates of groundwater losses and inputs such as cloud drip and
infiltration from septic tanks. Mean annual rainfall accumulation during a 7-year study (1991 to
1997) ranged from 1,722 mm in the Canóvanas watershed, to 4,235 mm in the Icacos and
Mameyes watersheds; the Cayaguás watershed had 2,172 mm. Combined runoff, groundwater
flow and withdrawals ranged from 47 to 73 percent of inputs (combined rainfall, cloud drip and
septic tank infiltration). Evapotranspiration, calculated as the water budget residual, amounted to
27, 40, 44, and 53 percent of total moisture inputs in the Icacos, Cayaguás, Mameyes, and
Canóvanas watersheds, respectively.