Northern Hemisphere Snowpacks, River Discharge and Settlement Dynamics - A Causal Analysis Using Passive Microwave SWE Data

Kurzfassung

Besides serving as the main freshwater resource for about 20% of the world’s human population, snow is also a crucial economic and environmental factor. However, in the context of climate change, snow reliability is diminishing due to declining snowpacks across the Northern Hemisphere and increasing variability in snow cover and melt patterns. Ecosystems and economic sectors dependent on snow, such as agriculture and hydropower, must adapt to these shifts and are reliant on robust data for informed decision-making. Our previous research, however, has shown that although the snowpack itself is thoroughly researched, the connection between snow and water availability, particularly on a large scale, remains underexplored. To address this gap, we performed a causal inference analysis across the Northern Hemisphere from 1980 to 2022, linking snow to river discharge while accounting for six additional influencing variables. The chosen causal inference approach (PCMCI) consists of two steps: causal discovery and causal effect estimation. In the causal discovery phase, a graph connecting the various variables is derived through a multitude of conditional independence tests. The causal effect estimation then fits a random forest regressor model to each time lag examined, allowing us to determine the effect of an intervention on the system, known as the causal effect. Using a moving window design, we evaluated the change in the causal effect of snowmelt on river discharge over the period from 1980 to 2022. This causal effect trend was then compared to other trends such as the river discharge itself, the SWE trends, rain trends, and glacier trends. Additionally, we incorporated the World Settlement Footprint (WSF) as a proxy for population dynamics, to gain insight into the potentially evolving freshwater demand within examined basins. At the Living Planet Symposium, we will present our methodology, and our results, showing the effect snowmelt has on river discharge. Additionally, we are to focus on similarity patterns among the examined regions, identifying areas where water stress could be linked to shifts in snowmelt dynamics. Finally, we compare the observed causal trends in snowmelt’s impact on river discharge with regional settlement trends to highlight areas where snow-driven reductions in river discharge coincide with possible increased water demand, suggesting potential intensification of water stress due to combined hydrological and societal factors.