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

摘要

Climate change and land use are rapidly changing the amount and temporaldistribution of recharge in northern aquifers. This paper presents a novelmethod for distributing Monte Carlo simulations of 1-D sandy sedimentprofile spatially to estimate transient recharge in an unconfined eskeraquifer. The modelling approach uses data-based estimates for the mostimportant parameters controlling the total amount (canopy cover) and timing(thickness of the unsaturated zone) of groundwater recharge. Scots pinecanopy was parameterized to leaf area index (LAI) using forestry inventorydata. Uncertainty in the parameters controlling sediment hydraulicproperties and evapotranspiration (ET) was carried over from the Monte Carlo runsto the final recharge estimates. Different mechanisms for lake, soil, andsnow evaporation and transpiration were used in the model set-up. Finally,the model output was validated with independent recharge estimates using thewater table fluctuation (WTF) method and baseflow estimation. The resultsindicated that LAI is important in controlling total recharge amount. Soilevaporation (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 showeddifferences in annual recharge of up to 100 mm. The uncertainty in rechargeestimates arising from the simulation parameters was lower than theinterannual variation caused by climate conditions. It proved important totake unsaturated thickness and vegetation cover into account when estimatingspatially and temporally distributed recharge in sandy unconfined aquifers.