Articles | Volume 19, issue 4
Research article
23 Apr 2015
Research article |  | 23 Apr 2015

Estimation of temporal and spatial variations in groundwater recharge in unconfined sand aquifers using Scots pine inventories

P. Ala-aho, P. M. Rossi, and B. Kløve

Abstract. Climate change and land use are rapidly changing the amount and temporal distribution of recharge in northern aquifers. This paper presents a novel method for distributing Monte Carlo simulations of 1-D sandy sediment profile spatially to estimate transient recharge in an unconfined esker aquifer. The modelling approach uses data-based estimates for the most important parameters controlling the total amount (canopy cover) and timing (thickness of the unsaturated zone) of groundwater recharge. Scots pine canopy was parameterized to leaf area index (LAI) using forestry inventory data. Uncertainty in the parameters controlling sediment hydraulic properties and evapotranspiration (ET) was carried over from the Monte Carlo runs to the final recharge estimates. Different mechanisms for lake, soil, and snow evaporation and transpiration were used in the model set-up. Finally, the model output was validated with independent recharge estimates using the water table fluctuation (WTF) method and baseflow estimation. The results indicated that LAI is important in controlling total recharge amount. Soil evaporation (SE) compensated for transpiration for areas with low LAI values, which may be significant in optimal management of forestry and recharge. Different forest management scenarios tested with the model showed differences in annual recharge of up to 100 mm. The uncertainty in recharge estimates arising from the simulation parameters was lower than the interannual variation caused by climate conditions. It proved important to take unsaturated thickness and vegetation cover into account when estimating spatially and temporally distributed recharge in sandy unconfined aquifers.

Short summary
We present a novel simulation method for estimating spatially distributed and transient groundwater recharge in unconfined sandy aquifers. The approach uses field data for the most important parameters affecting groundwater recharge and accounts for parameter uncertainty. The results show that tree canopy cover is the most important factor in controlling groundwater recharge at our study area. Tree canopy is thinned by forestry, which may lead to a significant increase of groundwater recharge.