Robin Thorne

Streamflow hydrology in the boreal region under the influences of climate and human interference

The boreal region has a subarctic climate that is subject to considerable inter-annual variability and is prone to impacts of future warming. Climate influences the seasonal streamflow regime which typically exhibits winter low flow, terminated by spring freshet, followed by summer flow recession. The effects of climatic variation on streamflow cannot be isolated with confidence but the impact of human regulation of rivers can greatly alter the natural flow rhythm, changing the timing of flow to suit human demands. The effect of scenario climate change on streamflow is explored through hydrological simulation. Example of a Canadian basin under warming scenario suggests that winter flow will increase, spring freshet dates will advance but peak flow will decline, as will summer flow due to enhanced evaporation. While this simulation was site specific, the results are qualitatively applicable to other boreal areas. Future studies should consider the role of human activities as their impacts on streamflow will be more profound than those due to climate change.

Comment on ‘Detection of hydrologic trends and variability’ by Burn, D.H. and Hag Elnur, M.A., 2002. Journal of Hydrology 255, 107–122

Abstract We are in agreement with Burn and Hag Elnur [J. Hydrol. 255 (2002) 107] that streamflow trends and variability are related to meteorological factors. We expanded the analysis of streamflow variability by relating annual peaks and spring (April, May, June) discharges to ENSO (El Nino–Southern Oscillation) events. Since geophysical considerations suggest that western Canada is warmer and drier than usual during El Nino but cooler and wetter under La Nina influences, flow variability of many western Canadian rivers is found to be correlated with winter values of such indices as the Southern Oscillation Index (SOI), Multivariate ENSO Index (MEI) or PNA (Pacific/North American Index). The spatial pattern of the non-parametric Spearmans r2 (for streamflow vs SOI) indicates a general correspondence with the correlation pattern of SOI-precipitation reported by Shabbar et al. [J. Climate 10 (1997) 3016]. This reinforces the linkage between streamflow variability, precipitation and climatic forcing.

Reference hydrologic networks II. Using reference hydrologic networks to assess climate-driven changes in streamflow

Abstract Reference hydrologic networks (RHNs) can play an important role in monitoring for changes in the hydrological regime related to climate variation and change. Currently, the literature concerning hydrological response to climate variations is complex and confounded by the combinations of many methods of analysis, wide variations in hydrology, and the inclusion of data series that include changes in land use, storage regulation and water use in addition to those of climate. Three case studies that illustrate a variety of approaches to the analysis of data from RHNs are presented and used, together with a summary of studies from the literature, to develop approaches for the investigation of changes in the hydrological regime at a continental or global scale, particularly for international comparison. We present recommendations for an analysis framework and the next steps to advance such an initiative. There is a particular focus on the desirability of establishing standardized procedures and methodologies for both the creation of new national RHNs and the systematic analysis of data derived from a collection of RHNs. Editor Z.W. Kundzewicz; Associate editor K. Hamed Citation Burn, D. H., et al., 2012. Reference hydrologic networks II. Using reference hydrologic networks to assess climate-driven changes in streamflow. Hydrological Sciences Journal, 57 (8), 1580–1593.

Simulating monthly streamflow for the Upper Changjiang, China, under climatic change scenarios.

Abstract The potential effect of climatic change on the flow of the Upper Changjiang (or Yangtze River) above the Three Gorges, China, was simulated with the SLURP hydrological model, using ERA40 data from 1961–1990 to simulate the baseline streamflow, and employing scenario temperature and precipitation changes depicted by two global climate models: the Hadley Centre and the Canadian climate model (CCCma) for both the B2 scenario (moderate emission of greenhouse gases) and the A2 scenario (more intense emission), for the 2021–2050 and 2071–2100 time horizons. In general, temperature and precipitation changes are more pronounced for the latter than for the former period. Winter low flows will not change but summer high flow may be augmented by increased precipitation. By mid-century, temperature increase will reduce streamflow according to CCCma, but not so under the Hadley Centre scenario. By the end of the century, precipitation will be great enough to overcome the influence of warming to raise discharge from most parts of the basin. The Min and the Jinsha rivers warrant much attention, the former because of its large flow contribution and the latter because of its sensitivity to climate forcing.

Lessons from Macroscale Hydrologic Modeling: Experience with the Hydrologic Model SLURP in the Mackenzie Basin

Macroscale models are used increasingly in hydrology to simulate regional responses to external forcing, to evaluate large basin management strategies, and to extend hydrologic data sets. The hydrologic model SLURP (Semidistributed Land Use-based Runoff Processes) is a semi-distributed model that has been successfully applied to basins of various sizes, notably those in cold regions. The SLURP manual provides explanations of computational algorithms, sets of commonly applicable parameter values, and computational steps required to run the model. Although the manual offers much information, users can benefit from additional information on certain procedures in order to operate the model successfully. In this chapter we share our experiences in operating this model, including the preparation of input data, initialization of variables, optimization of parameters, and validation of model results. We suggest that the lessons learned from the use of SLURP can be applied to other macroscale hydrologic models.

Short-term selective thinning effects on hydraulic functionality of a temperate pine forest in eastern Canada

Forest plantations are commonly used to restore the ecological and hydrological functionality of landscapes. In this study, we investigated the hydrological response of a 74-year-old pine plantation forest in southern Ontario, Canada to a selective thinning, wherein 30% of trees were harvested in winter of 2012. Tree-level and ecosystem-level water fluxes were monitored from 2011 to 2013 using sapflow and eddy-covariance techniques, and were compared with an adjacent 39-year-old pine plantation forest that was not thinned. In the 74-year-old forest, transpiration declined after thinning in the 2012 growing season, while tree-level water transport increased despite a severe drought. Time lag between sapflow and ecosystem evapotranspiration showed that the older stand had a significantly shorter time lag when compared to the younger stand, particularly in the thinning year. Linear regression modeling indicated that this was likely due to higher soil moisture status in the older stand versus the younger forest. Hydraulic redistribution of soil water was apparent during drought periods in both forests and did not appear to be negatively affected by the thinning treatment in the older forest. We conclude that selective low density thinning did not negatively impact the forests response to seasonal drought, and that the availability of more soil moisture as a result of thinning may improve the resilience of the forest to future climatic extreme events such as drought.