Climate change impact on the hydrometeorological drought propagation

Hydrometeorological droughts are complex hazards that cover wide areas with typically slow-onset and can affect different social, economic, environmental sectors at different spatial and temporal scales. However, it is challenging to investigate changes in hydrometeorological drought and their propagation from precipitation deficit, to soil moisture, discharge and groundwater deficits and to ascertain to what extent climatic change may affect drought characteristics (e.g. magnitude, frequency and duration). This research explores changes in hydrometeorological drought characteristics and their propagation from meteorological to hydrological drought states using climate model simulations from CMIP6 to force a conceptual hydrological model. Using a sample of 30 catchments in Ireland, we examine changes in hydrometeorological drought using standardised indices of precipitation (SPI), soil moisture deficits (SPEI), runoff (SRI) and baseflow (SBI). We find that downscaled CMIP6 projections are poor at capturing droughts at shorter timescales, however performance increases depending on bias correction technique and drought accumulation period. Largest uncertainties in drought projections emanate from climate models, outweighing the role of hydrological model parameter uncertainty, bias correction and emissions scenarios. Projected changes in drought characteristics strongly covary for SPI and SPEI, however covariation in changes is weaker for SRI and SBI. The propagation of meteorological to hydrological drought increases over time, with proportional increases for moderate, severe and extreme droughts. Across the catchment sample the average lag time between meteorological and hydrological drought occurrence in the baseline period is 3-5 months, with lag times likely to increase with climate change. Therefore, results suggest that while the propagation of meteorological droughts to hydrological events (SRI/SBI), increases, the time taken for precipitation anomalies to become apparent in hydrological variables increases. Such changes in drought propagation need to be considered in adaptation planning.