[1] Understanding low impact development (LID) planning and best management practices (BMPs) effects on recharge is important because of the increasing use of LID BMPs to reduce storm water runoff and improve surface-water quality. LID BMPs are microscale, decentralized management techniques such as vegetated systems, pervious pavement, and infiltration trenches to capture, reduce, filter, and slow storm water runoff. Some BMPs may enhance recharge, which has often been considered a secondary management benefit. Here we report results of a field and HYDRUS-2D modeling study in San Francisco, California, USA to quantify urban recharge rates, volumes, and efficiency beneath a LID BMP infiltration trench and irrigated lawn considering historical El Niño/Southern Oscillation (ENSO) variability and future climate change using simulated precipitation from the Geophysical Fluid Dynamic Laboratory (GFDL) A1F1 climate scenario. We find that in situ and modeling methods are complementary, particularly for simulating historical and future recharge scenarios, and the in situ data are critical for accurately estimating recharge under current conditions. Observed (2011–2012) and future (2099–2100) recharge rates beneath the infiltration trench (1750–3710 mm yr⁻¹) were an order of magnitude greater than beneath the irrigated lawn (130–730 mm yr⁻¹). Beneath the infiltration trench, recharge rates ranged from 1390 to 5840 mm yr⁻¹ and averaged 3410 mm yr⁻¹ for El Niño years (1954–2012) and from 1540 to 3330 mm yr⁻¹ and averaged 2430 mm yr⁻¹ for La Niña years. We demonstrate a clear benefit for recharge and local groundwater resources using LID BMPs.

Groundwater resources are directly affected by climate variability via precipitation, evapotranspiration and recharge. Analyses of US and India trends reveal that climate-induced pumping indirectly influences groundwater depletion as well.

Low impact development (LID) best management practices (BMPs) collect, infiltrate, and treat stormwater runoff, and increase recharge to aquifers. Understanding the controls on reduction/oxidation (redox) conditions within LID BMPs is important for groundwater management because outflow from some LID BMPs can recharge aquifers and affect groundwater quality. Here we evaluate redox conditions of urban stormwater runoff in a LID infiltration trench in San Francisco, California, and quantify the relation between water saturation (%) and temperature (◦C) and resulting dissolved oxygen (DO) concentrations, redox dynamics, and O₂ reduction rates. The DO fluctuations ha ve an inverse response to the duration of saturation of the trench. Anoxic (<0.5 mg/L) conditions often occurred within hours of stormwater events and persisted from a few hours to two days, which indicate that microbial respiration can be a limiting factor for DO. Temperature of stormwater runoff was not a statistically significant control on DO. The estimated O₂ reduction rate is 0.003mg·L-1·min-1, which is two to five orders of magnitude higher than in groundwater from previous studies. Higher rates of O₂ reduction are a function of the more toxic and organic-rich stormwater runoff that drives faster microbial O₂ reduction. Our findings have important implications for the design of infiltration trenches and other LID BMPs to achieve desired redox conditions for infiltrating stormwater toward minimizing groundwater contamination.