Regional Groundwater Flow Model and Physical Assessment of groundwater-related ecosystem services

Description

This is the regional-scale pair that describes the Medina del Campo aquifer as a whole. The groundwater flow model, built in iMOD on the MODFLOW code from the three-dimensional geological model, simulates the response of the water table to abstraction across the entire groundwater body at 500 metre resolution. It is run under two conditions: a pristine state with average recharge and no pumping, and an anthropic state with the actual pumping record.

The comparison between the two runs is the finding. Under pristine conditions the water table slopes regionally from south to north, the rivers are connected to the aquifer and drain into it along their length, and shallow groundwater supports lagoons close to the Zapardiel. Under pumping, the water table falls by between five and twenty metres across the areas of concentrated abstraction, the rivers become disconnected from the aquifer in places, and the springs that formerly reached the surface are reduced in number.

Alongside the flow model, the physical assessment of groundwater-related ecosystem services converts those head changes into changes in service delivery, so that the effect of a management option can be read as an effect on the services people actually use.

Applications to decision making in the insurance sector

The model produces the quantitative statement that a risk-based argument for intervention requires: how much the water table has fallen, where, and at what rate it responds to a change in abstraction. It also supports the scenario work in which abstraction and precipitation futures are combined to 2050 and beyond, which shows whether a measure removes the drought exposure or merely postpones it.

Added value of this modelling approach

It separates the natural behaviour of the aquifer from the effect of human use. That separation is what allows the contribution of abstraction to the problem — and therefore the effect of changing it — to be quantified rather than asserted.

What decision can be improved with this modelling approach

How far abstraction must fall for the water table to stabilise; which parts of the body respond fastest to recharge; and how the rivers, wetlands and abstractions interact under a changed climate.