Abstract
Abstract. Groundwater plays an important role in the terrestrial water cycle, interacting with the land surface via vertical fluxes through the water table and distributing water resources spatially via gravity-driven lateral transport. It is therefore essential to have a correct representation of groundwater processes in land surface models, as land–atmosphere coupling is a key factor in climate research. Here we use the LEAFHYDRO land surface and groundwater model to study the groundwater influence on soil moisture distribution and memory, and evapotranspiration (ET) fluxes in the Iberian Peninsula over a 10-year period. We validate our results with time series of observed water table depth from 623 stations covering different regions of the Iberian Peninsula, showing that the model produces a realistic water table, shallower in valleys and deeper under hilltops. We find patterns of shallow water table and strong groundwater–land surface coupling over extended interior semi-arid regions and river valleys. We show a strong seasonal and interannual persistence of the water table, which induces bimodal memory in the soil moisture fields; soil moisture “remembers” past wet conditions, buffering drought effects, and also past dry conditions, causing a delay in drought recovery. The effects on land–atmosphere fluxes are found to be significant: on average over the region, ET is 17.4 % higher when compared with a baseline simulation with LEAFHYDRO's groundwater scheme deactivated. The maximum ET increase occurs in summer (34.9 %; 0.54 mm d−1). The ET enhancement is larger over the drier southern basins, where ET is water limited (e.g. the Guadalquivir basin and the Mediterranean Segura basin), than in the northern Miño/Minho basin, where ET is more energy limited than water limited. In terms of river flow, we show how dry season baseflow is sustained by groundwater originating from accumulated recharge during the wet season, improving significantly on a free-drain approach, where baseflow comes from water draining through the top soil, resulting in rivers drying out in summer. Convective precipitation enhancement through local moisture recycling over the semi-arid interior regions and summer cooling are potential implications of these groundwater effects on climate over the Iberian Peninsula. Fully coupled land surface and climate model simulations are needed to elucidate this question.
Highlights
Groundwater dynamics and its interactions with the land– atmosphere system play a key role in the terrestrial water cycle
An accurate estimation of the net recharge is of major importance for water management systems, mainly over highirrigation areas such as the semi-arid regions of the Iberian Peninsula, as it will help to understand where unconfined aquifers are at risk of being overexploited
As a first result, we present the net recharge estimation produced by our long-term land surface models (LSMs) simulation with a fully dynamic water table (WT), where upward capillary fluxes are accounted for (Fig. 7a)
Summary
Groundwater dynamics and its interactions with the land– atmosphere system play a key role in the terrestrial water cycle. Groundwater exchanges with the land surface occur via vertical fluxes through the water table surface and horizontal water redistribution via gravity-driven lateral transport within the saturated zone. The Iberian Peninsula, with a typical Mediterranean climate of the dry growing season, is one such region where ET is largely constrained by water availability. Soil moisture memory refers to the persistence of wet or dry anomalies in the soil after the atmospheric conditions that caused them have passed. If there is high land– atmosphere coupling, that is, if the conditions of the soil can have a significant impact on atmospheric dynamics, soil moisture memory can influence weather conditions, with major implications for seasonal and long-term forecasting
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