Root-Zone Water-Storage Capacity and Uncertainty: An Intrinsic Factor Affecting Agroecosystem Resilience to Drought

Abstract

Mapping ecosystem function indicators helps identify areas susceptible to drought, heat stress, and reduced agricultural production. This information can be used to prioritize areas for targeted interventions to tackle adverse climatic conditions and changes in land use. Root-zone water-storage capacity (S_R) is a commonly used variable of agroecosystem functioning, representing the maximum value of water stored within the root zone and accessible to vegetation for its productive growth. Mapping S_R over large spatial scales is only feasible through an oversimplification of real-world conditions. Under such circumstances, we propose to resort to soil-hydraulic-energy indices, namely the integral mean water capacity (IMWC) and the integral energy (IE) and an effective root-zone depth (z_R). Accordingly, a more efficient and environmentally sensitive, albeit still simplistic, determination of the root-zone water-storage capacity is computed as S_R,IMWC = z_R × IMWC, and validated against soil moisture measurements carried out along a transect. Subsequently, the S_R,IMWC indicator was mapped in Campania, a 13,700 km² region in southern Italy. This study also addressed the issue of the propagation of epistemic uncertainty in input soil hydraulic parameters to the output response variable IMWC. This was accomplished using a Monte Carlo simulation technique that generated several equiprobable stochastic realizations from the multivariate set of data inputs. Finally, we assessed the potential utility of the integral capacity energy (ICE) composite indicator, computed as the ratio IMWC/IE in %, as a scoring parameter to identify Priority Intervention Areas (PIAs) where resilience to environmental challenges, including water scarcity, drought events, and post-fire conditions, could be enhanced.