Defining thresholds and lags times in drought propagation cascade: a study case in the northern Córdoba (southern Spain)

Sustainable water resources management constitutes a critical challenge in Mediterranean regions, where water availability is limited. In addition, over these areas climate change projections point to an increasement of frequency and recurrency of extreme events, such as drought, which further intensification of scarcity conditions. Historically, these regions have addressed their climate variability through regulation and storage infrastructures. However, the resulting increase in water availability caused by this infrastructure has promoted the development of highly water-dependent socioeconomic systems (e.g. irrigated agriculture, energy production or tourism), thereby increasing their vulnerability to these extreme events such as drought.  

Drought is a complex phenomenon composed of multiple stages interconnected through a propagation cascade: meteorological drought, driven by precipitation deficits; agricultural drought, linked to soil moisture and vegetation water requirements; hydrological drought, reflected in reduced streamflow and reservoir storage; and socioeconomic drought, which emerges when water shortages impact human activities and services. In this sense, a precipitation deficit does not immediately translate into a reduction in soil moisture or a decrease in streamflow, as drought propagation is modulated by propagation thresholds and lags times. The magnitude and duration of these lags are controlled by multiple factors such as soil characteristics, land uses, and reservoir operation. In Mediterranean mid- mountains catchment this complexity increases due to the variability in precipitation patterns, a complex soil-land interaction and the ephemeral character of the streams.  

In this context, this work analyses the thresholds that trigger the concatenation of droughts and the lag times along the drought propagation cascade in medium-sized Mediterranean mountain basins, with the aim of improving the anticipation and management of water scarcity episodes. The analysis focuses on the northern area of Córdoba regions (southern Spain), where recent drought episodes had had a significant impact on water resources availability, exposing structural vulnerabilities in the supplying system. 80,000 citizens were without running water at home for more than a year.  

A distributed, physically based hydrological model is applied to generate catchment-averaged precipitation, streamflow, and soil moisture for the period 1960-2024. Drought propagation thresholds and lags are quantified through a comparative analysis of standardized drought indices, including the Standardized Precipitation Index (SPI), Standardized Streamflow Index (SSFI), and Soil Moisture Anomaly (SMA), combined with time-series techniques such as cross-correlation and autocorrelation analyses. Finally, the potential benefits of incorporating these identified lags into operational water management will be evaluated, highlighting their value for strengthening early warning systems and water resources planning.  

Acknowledgements: This study has been funded by the call “Grants to develop innovative solutions to address drought, within the framework of the PLAnd Drought Andalusia. 2023 Call” through the project PLSQ-00172-F – “Service for the early detection of alert states in water management under scarcity conditions” (SEGA)