Surface Hydrology Model

Description

A catchment that suffers both drought and flooding has to be described in both directions, and this model does that for the Medina del Campo area. On the drought side it computes standardised precipitation and evapotranspiration indices — SPEI at three-month, twenty-four-month and forty-eight-month accumulation periods — which express the water deficit of a period relative to the local climate. Because the index depends only on rainfall and temperature, it can be compared between regions and between periods, and it detects the slow, cumulative droughts that matter in a semi-arid basin rather than only the dramatic ones.

On the flood side it applies a two-dimensional hydraulic flow model to a probabilistic analysis of anomalous rainfall, producing flow depths for a given probability of occurrence. The result is a measure that can be linked to damage likelihood, which is what connects the physical model to the economic assessment.

The model provides the climate and hazard context within which the groundwater, allocation and ecosystem service models operate, and it supplies the scenarios that the integrated metamodel uses.

Applications to decision making in the insurance sector

Drought is a slow-onset hazard that accumulates across seasons and is not well captured by event-based assessment. The indices make the accumulation visible and comparable over long periods, which is what a risk assessment of a water-dependent exposure needs. On the flood side, the probabilistic treatment produces the hazard frequency that a loss estimate requires.

Added value of this modelling approach

It treats drought and flood as two aspects of one water balance rather than as separate hazards, which is the only way to assess a measure that shifts water from one to the other — recharge, for instance, which reduces drought exposure by taking water out of the flood peak.

What decision can be improved with this modelling approach

How severe a drought the system must be able to withstand; whether a recharge intervention is taking water that would have caused flood damage; and how the frequency of both hazards changes under a projected climate.