Testing the predictive ability of a karst subsidence susceptibility map made thirty years ago in the central Ebro Basin (Zaragoza, Spain)

Karst subsidence has caused damage in numerous buildings and infrastructures in the surroundings of Zaragoza city since the early 1970s, when rapid urbanization of the area begun. A detailed survey carried out in 1991 allowed recognizing and mapping damages in an industrial district, and elaborating a susceptibility or spatial hazard map based on (i) the observed presence of active alluvial dolines, and (ii) spatial distribution of factors controlling their development, according to a hazard model based on both spatial analysis and laboratory experimental simulation. The predictive ability of such spatial hazard map is now tested, thirty years later, by a new detailed field survey carried out in 2021 covering almost the same area. The results allow mapping of the total present-day damage and, using GIS tools, also a residual map of areas newly damaged since 1991. After comparing those maps with the hazard zonation proposed in 1991, we conclude that: (i) the predictive ability of the latter is good in overall; (ii) the areas of highest subsidence hazard have a probability in the range of 19–38% of suffering damage over a 30-year period, while this probability systematically decreases up to about 7% for the lowest hazard areas; (iii) the average rate of occurrence of new damage within the overall study zone has remained quite uniform around 0.5% in area per year. Incorporating such calculations of temporal probability of occurrence associated to each hazard category allows the original susceptibility map to approach a hazard s.s. map, providing annual probabilities of occurrence between ~ 0.6 to 1.3% and ~ 0.3% for the distinct hazard zones.