Dynamics of dissolved organic carbon during drought and flood events: A phase-by-stages perspective

Accounting for model parameter uncertainty provides more robust projections of dissolved organic carbon dynamics to aid drinking water management

Changes in climate and human behaviour impact catchment hydrology and the export of nutrients including dissolved organic carbon (DOC), with consequences for drinking water supply. In this study, we projected future river discharge and DOC dynamics under three Shared Socioeconomic Pathways (i.e., different futures of climatic conditions, socio-economic development and adaptation to climate change) and quantified change relative to a baseline for two contrasting catchments: one in Sweden and one in Ireland. For this, we used the Generalised Watershed Loading Functions Model (GWLF) with an integrated DOC module (GWLF-DOC) and drove it with data from an ensemble of global climate models, taking into account variability derived from multiple model parameter sets. We assessed the relative contribution of each of these two factors (climate input data and model parameterisation) to the total uncertainty in predictions. Projections for river discharge differed between the two sites in magnitude, variability and direction of change depending on the future scenario and time period. In contrast, DOC was always projected to show increases in concentration throughout the annual cycle and over time, with the highest levels by the end of the century, for scenarios with greater warming and low mitigation efforts. Future climate data provided the dominant source of uncertainty in all of our projections. However, the DOC model parameters, which respond to temperature and soil moisture conditions, became more influential in scenarios of higher climatic variability. Our approach highlights the benefits of incorporating often ignored parameter uncertainty in climate change impact assessments for both interpreting outputs and communicating results to water managers.

Enhanced Role of Streamflow Processes in the Evolutionary Trends of Dissolved Organic Carbon

Investigating dissolved organic carbon (DOC) dynamics and drivers in rivers enhances the understanding of carbon-environment linkages and support sustainability. Previous studies did not fully consider the dynamic nature of key drivers that influence the long-term changing trends in DOC concentration over time (the controlling factors and their roles in DOC trend can undergo alterations over time). We analyzed 42 years (1979-2018) of hydrometeorology, sulfate SO4, and DOC data from a 5.42 km2 watershed in central-southern Ontario, Canada. Our findings reveal a significant (p ≤ 0.01) overall increase in DOC concentrations, mainly due to the coevolution of SO4 and streamflow trends, especially the extreme flows. Over the 42-year period, the changing trend of streamflow (especially the extreme high or low flows) have significantly (p < 0.05) intensified their influence on DOC trends, increasing by an average of 30%. Conversely, the impact of SO4 has weakened, experiencing an average decrease of 32.6%. The upward trend in the annual average DOC concentration is attributed to the increasing number of maximum flow days within a year, while the decreasing trend in the number of minimum flow days has a contrasting effect. In other words, changes in maximum and minimum flow days have a counteracting effect on the DOC concentration trends. These results underscore the importance of considering the effects of altered streamflow processes on carbon cycle changes under evolving environmental conditions.

A review of recent developments on drought characterization, propagation, and influential factors

Droughts have impacted human society throughout its history. However, the occurrence of severe drought events in the last century and the concerns on the potential effects of climate change have prompted remarkable advances in drought conceptualization and modeling in recent years. This review intends to present the state-of-the-art on drought characterization and propagation, as well as providing insights on how climate dynamics and anthropogenic activities might affect this phenomenon. For this purpose, we first address the distinct concepts of droughts and their relationships. Next, we present two frequently utilized methods based on the run theory for drought characterization and explain the development and recovery stages of droughts. Then, we discuss potential drivers for drought occurrence and propagation, with focus on meteorological factors, catchments' physical characteristics and human activities. Later, we describe how droughts can affect several parameters of water quality. This review also addressed flash droughts, encompassing their definitions, commonly used indices, and potential drivers. Finally, we briefly address the roles of climate change and long-term persistence on future drought scenarios. This review may be useful for researchers and stakeholders for attaining a broader understanding on drought dynamics and impacts.