Bottom-up vulnerability assessment for climate change adaptation in water resource systemsintegrating weather generators and hydroeconomic and ecosystem modelling

Abstract

Traditional evaluations of the impact of climate change scenarios in water resource management involve top-down approaches, based on predictions from global climate models (GCMs). In contrast, bottom-up strategies provide a more comprehensive understanding of the system's behaviour applying a wide range of climate scenarios based on parametric climatic alterations. By doing so, climate change impacts and subsequent adaptation measures can be assessed taking into account the limits of their availability and how their performance level varies depending on the changing climate conditions, which is quite useful especially when faced with substantial uncertainty. This study develops a bottom-up approach to evaluate climate change impacts combining weather generators to obtain a wide range of future climates based on parametric alternations of the main climatic patterns; hydroeconomic models to assess the costs and benefits associated with those impacts; and ecosystem models to evaluate how the habitat of fish species would be impacted by climate change. The weather generator for climate variables (precipitation, temperature, and evapotranspiration) is coupled with a parameter-lumped conceptual hydrological model to generate future time series of streamflow, which are further integrated into a hydroeconomic model that simulate reservoir operation and assesses the economic performance of the river basin water uses. The weather generator is implemented using MATLAB, in which the annual temperature is modelled by an AR(2) autoregressive model, while annual precipitation follows an AR(0) autoregressive model. Monthly time series are obtained through the method of fragments. The correlation between subbasins is modelled using a linear relationship of the residuals. Monthly evapotranspiration is computed by applying a transformation factor linked to monthly temperature, smoothed through a Fourier Transform series. The conceptual hydrological model is also implemented in a MATLAB script that transforms climate variables into streamflows, which serve as input for the hydroeconomic model of the basin. The methodology was applied to the semi-arid Jucar River Basin (JRB) in Spain, characterized by multi-annual droughts combined with significant development of irrigated agriculture, which implies a distinct vulnerability to climate change impacts. The methodology maps climate change impacts, defined as parametric changes of precipitation (% of change) and temperature (increase in ºC), to economic benefits and fish habitat. Results show how the economic and environmental performance of the JRB are affected by climate changes, and determines when tipping points demanding adaptation are reached, locating the areas in which the impacts steeply increase. Acknowledgements: This study has received funding from the SOS-WATER project under the European Union’s Horizon Europe research and innovation programme under (GA No. 101059264).