Papers by Markus Schnorbus
Journal of Hydrometeorology
We describe a state-of-the-art framework for projecting hydrologic impacts due to enhanced warmin... more We describe a state-of-the-art framework for projecting hydrologic impacts due to enhanced warming and amplified moisture fluxes in the subarctic environment under anthropogenic climate change. We projected future hydrologic changes based on phase 5 of the Coupled Model Intercomparison Project global climate model simulations using the Variable Infiltration Capacity hydrologic model and a multivariate bias correction/downscaling method for the Liard basin in subarctic northwestern Canada. Subsequently, the variable importance of key climatic controls on a set of hydrologic indicators was analyzed using the random forests statistical model. Results indicate that enhanced warming and wetness by the end of century would lead to pronounced declines in annual and monthly snow water equivalent (SWE) and earlier maximum SWE. Prominent changes in the streamflow regime include increased annual mean and minimum flows, earlier maximum flows, and either increased or decreased maximum flows depe...
Water Resources Research, 2010
Citation: Alila, Y., R. Hudson, PK Kuraś, M. Schnorbus, and K. Rasouli (2010), Reply to comment b... more Citation: Alila, Y., R. Hudson, PK Kuraś, M. Schnorbus, and K. Rasouli (2010), Reply to comment by Jack Lewis et al. on Forests and floods: A new paradigm sheds light on age-old controversies, Water Resour. Res., 46, W05802, doi:10.1029/2009WR009028.
Hydrological Processes, 2016
The debate regarding peak flow responses to forest clearcutting and road building in the maritime... more The debate regarding peak flow responses to forest clearcutting and road building in the maritime regions of the Pacific Northwest has attracted much attention over the past several decades and its outcome is an important scientific and operational concern. Although there appears to be general consensus that small peak discharge events are increased following forest management activities, little conclusive evidence exists regarding the impact of forest management activities on large events. Statistical tests in traditional paired watershed studies have been used to accept or reject hypotheses regarding peak flow responses to clearcutting and roads but provided no insight into watershed processes and other factors leading to their outcome. Furthermore, statistical analyses of peak flow responses to forestry activities in traditional paired watershed studies are confounded by the many factors that may contribute to management effects on watershed hydrology as well as by issues such as...
Water Resources Research, 2014
ABSTRACT A recent hydrological impacts study in British Columbia, Canada used an ensemble of 23 c... more ABSTRACT A recent hydrological impacts study in British Columbia, Canada used an ensemble of 23 climate change simulations to assess potential future changes in streamflow. These Coupled Model Intercomparison Project, phase 3 (CMIP3) simulations were statistically downscaled and used to drive the Variable Infiltration Capacity (VIC) hydrology model over several watersheds. Due to computational restrictions, the 23 member VIC ensemble is a subset of the full 136-member CMIP3 archive. Extending the VIC ensemble to cover the full range of uncertainty represented by CMIP3, and incorporating the latest generation CMIP5 ensembles, poses a considerable computing challenge. Thus, we extend the VIC ensemble using a computationally-efficient statistical emulation model, which approximates the combined output of the two-step process of statistical downscaling and hydrologic modeling, trained with the 23 member VIC ensemble. Regularized multiple linear regression links projected changes in monthly temperature and precipitation with projected changes in monthly streamflow over the Fraser and Peace River watersheds. Following validation, the statistical emulator is forced with the full suite of CMIP3 and CMIP5 climate change projections. The 23 member VIC ensemble has a smaller spread than the full ensemble; however, both ensembles provide the same consensus estimate of monthly streamflow change. Qualitatively, CMIP5 shows a similar streamflow response as CMIP3 for snow-dominated hydrologic regimes. However, by end-century the CMIP5 worst-case RCP8.5 has a larger impact than CMIP3 A2. This work also underscores the advantage of using emulation to rapidly identify those future extreme projections that may merit further study using more computationally-demanding process-based methods.
ABSTRACT Continued warming and changing precipitation patterns will have a large effect on the hy... more ABSTRACT Continued warming and changing precipitation patterns will have a large effect on the hydrology of British Columbia (BC), with the possibility for subsequent impacts to various ecological and water-related resources and activities. Throughout most of BC, seasonal runoff is either snow-dominated (nival regimes), or snow influenced (hybrid nival-pluvial or nival-glacial regimes), which makes the region particularly susceptible to the effects of climate change. However, the hydro-climatology of British Columbia (BC) is spatially complex and it is expected that seasonal hydrologic impacts will vary regionally. To explore this regional variability, two watersheds with unique hydro-climatic settings were analyzed for their response to projections of future climate change. The Campbell River watershed in south-western BC experiences a coastal climate of mild wet winters and warm dry summers and, due to a large elevation range, the basin exhibits a mixed nival-pluvial hydrologic regime. The Upper Peace River basin, located in north-eastern BC, has a typical continental climate and possesses a nival hydrologic regime. Hydrologic changes were estimated based on temperature and precipitation projections from eight Global Climate Models (GCMs) from the CMIP3 project, run under three IPCC SRES emissions scenarios, and statistically downscaled, for a total of 23 combinations (not all scenarios were available for all GCMs). These transient scenarios provide projections that range from a future with relatively less warming and moistening ("cool/dry") to relatively more warming and moistening ("warm/wet"). This ensemble approach explicitly addresses both emissions and GCM uncertainty in the final suite of climate projections. Hydrologic impacts were then assessed by using the downscaled climate projections to force the Variable Infiltration Capacity (VIC) hydrologic model. Hydrologic impacts were estimated by comparing the future period 2041 to 2071 (i.e., the 2050s) to the 1961 to 1990 historical baseline (the 1970s). The major hydrologic response in both basins is a change in the dynamics of seasonal snow storage, including changes in the proportion of winter precipitation as rainfall versus snowfall, seasonal snow accumulation, and the timing and magnitude of snowmelt. These changes results in seasonal changes in the timing of snow cover, soil moisture storage and drawdown, evaporation, transpiration and streamflow. For instance, both basins exhibit a consistent signal of increased winter (DJF) discharge, earlier onset of spring melt, and a decrease in summer (JJA) flows, resulting in an extension in the warm hydrologic season. The resulting changes in snow storage dynamics are strongly affected by elevation, generating large spatial variation in regions of complex topography. Also, hybrid nival-pluvial systems tend to be more sensitive to changes in both temperature and precipitation.
Journal of Hydrometeorology, 2015
Recent improvements in forecast skill of the climate system by dynamical climate models could lea... more Recent improvements in forecast skill of the climate system by dynamical climate models could lead to improvements in seasonal streamflow predictions. This study evaluates the hydrologic prediction skill of a dynamical climate model–driven hydrologic prediction system (CM-HPS), based on an ensemble of statistically downscaled outputs from the Canadian Seasonal to Interannual Prediction System (CanSIPS). For comparison, historical and future climate traces–driven ensemble streamflow prediction (ESP) was employed. The Variable Infiltration Capacity model (VIC) hydrologic model setup for the Fraser River basin, British Columbia, Canada, was used as a test bed for the two systems. In both cases, results revealed limited precipitation prediction skill. For streamflow prediction, the ESP approach has very limited or no correlation skill beyond the months influenced by initial hydrologic conditions, while the CM-HPS has moderately better correlation skill, attributable to the enhanced temp...
The Distributed Hydrology Soil Vegetation Model in conjunction with synthetic climate data was us... more The Distributed Hydrology Soil Vegetation Model in conjunction with synthetic climate data was used to investigate the impact of forest harvesting upon the peak annual discharge regime of two headwater streams, 240 and 241 Creeks, in south-central British Columbia (BC). For return periods (T) in the range of 1.25 to 100 years, simulated quantile magnitude (Q T) increases over the control value with increasing clearcut harvest area, represented as a proportion of basin area. This general trend is independent of the temporal scale of discharge, as represented by hourly, daily, and 7-day streamflow. For both 240 and 241 Creeks Q T increases are consistently statistically significant (α = 0.05) at proportion harvest areas ≥ 30%. Fitted Generalized Extreme Values (GEV) distributions suggest that for a snowmelt dominated peak discharge regime, relative (to control) post-harvest quantile change (∆Q T) increases with increasing return period, with no apparent asymptotic limit. However, this trend substantially overestimates the postharvest response of the most extreme peak discharge event for the simulated record (Control T > 100 years), which is entirely rainfall driven. Pooled ∆Q T results indicate that the relationship between ∆Q T and harvest area is quite strong and suggests that, regionally, the peak discharge response can be predicted using only harvest area as the predictor variable. However, for hourly discharge the effect of harvest elevation (categorized as occurring either above or below the median elevation for each basin) ads uncertainty to the pooled ∆Q T-area relationship. Closer examination of the ∆Q T response for 240 Creek suggests that at the spatial scale characteristic of the study area the hourly response relates to the relative apportionment of melt runoff into either a fast surface or slow sub-surface component. As such, the elevation dependence of hourly ∆Q T is related to the significant spatial discontinuity in drainage density that occurs at the H50 elevation; a morphologic characteristic that may or may not be representative of southcentral BC. At the daily and 7-day temporal scale differences in flow path travel times are less significant and ∆Q T exhibits only moderate elevation dependence.
Water Resources Research, 2013
ABSTRACT [1] Numerical modeling in conjunction with a stochastic weather generator was used to in... more ABSTRACT [1] Numerical modeling in conjunction with a stochastic weather generator was used to investigate the immediate impact of forest harvesting upon the annual-maximum peak discharge regime of 240 Creek, a snow-dominated headwater basin of low relief located in south-central British Columbia (BC), Canada. Harvesting effects were simulated using 11 hypothetical harvest scenarios that specifically assess the impact of clear-cut harvesting in the absence of roads. Distribution statistics show that the annual-maximum peak flow frequency curve for hourly discharge is affected both by harvest area, AH, and by harvest elevation, ZH. Annual peak discharge magnitude tends to increase with increasing AH, but decreasing ZH. Forest harvesting does not have a statistically significant (α = 0.05) impact on the peak flow distribution until AH ≥ 20% to 30%, depending on the statistical comparison used. There is no substantial elevation gradient in snow accumulation within 240 Creek, and the sensitivity of the hourly peak discharge regime to ZH is instead related to the spatial variation of channel density with elevation. Flood frequency analysis was used to directly compare control and treatment events of equal frequency of occurrence, using return periods, T, of 1.003–100 years. This analysis indicates that, contrary to the prevalent hydrological wisdom and regardless of AH and ZH, the relative increase in peak discharge quantiles (ΔQT) increases with increasing event magnitude (increasing T) for events equal to or larger than the median (T = 2 years) event. Overall, ΔQT ranges from 7% for AH = 30% to 84% for AH = 100%. The magnitude of peak flow change is found to be a function of changes in both net 48-h input fluxes (rainfall plus snowmelt minus evapotranspiration) and changes in snowmelt runoff synchronization, which directly affect treatment peak discharge magnitude and timing.
Water Resources Research, 2009
The science of forests and floods is embroiled in conflict and is in urgent need of reevaluation ... more The science of forests and floods is embroiled in conflict and is in urgent need of reevaluation in light of changing climates, insect epidemics, logging, and deforestation worldwide. Here we show how an inappropriate pairing of floods by meteorological input in analysis of covariance (ANCOVA) and analysis of variance (ANOVA), statistical tests used extensively for evaluating the effects of forest harvesting on floods smaller and larger than an average event, leads to incorrect estimates of changes in flood magnitude because neither the tests nor the pairing account for changes in flood frequency. We also illustrate how ANCOVA and ANOVA, originally designed for detecting changes in means, do not account for any forest harvesting induced change in variance and its critical effects on the frequency and magnitude of larger floods. The outcomes of numerous studies, which applied ANCOVA and ANOVA inappropriately, are based on logical fallacies and have contributed to an ever widening disparity between science, public perception, and often land-management policies for decades. We demonstrate how only an approach that pairs floods by similar frequency, well established in other disciplines, can evaluate the effects of forest harvesting on the inextricably linked magnitude and frequency of floods. We call for a reevaluation of past studies and the century-old, preconceived, and indefensible paradigm that shaped our scientific perception of the relation between forests, floods, and the biophysical environment.
Journal of Hydrometeorology, 2014
This study analyzed potential hydroclimatic change in the Peace River basin in the province of Br... more This study analyzed potential hydroclimatic change in the Peace River basin in the province of British Columbia, Canada, based on two structurally different approaches: (i) statistically downscaled global climate models (GCMs) using the bias-corrected spatial disaggregation (BCSD) and (ii) dynamically downscaled GCM with the Canadian Regional Climate Model (CRCM). Additionally, simulated hydrologic changes from the GCM–BCSD-driven Variable Infiltration Capacity (VIC) model were compared to the CRCM integrated Canadian Land Surface Scheme (CLASS) output. The results show good agreements of the GCM–BCSD–VIC simulated precipitation, temperature, and runoff with observations, while the CRCM-simulated results differ substantially from observations. Nevertheless, differences (between the 2050s and 1970s) obtained from the two approaches are qualitatively similar for precipitation and temperature, although they are substantially different for snow water equivalent and runoff. The results o...
Hydrological Processes, 2013
ABSTRACT It is a common practice to employ hydrologic models for assessing alterations to streamf... more ABSTRACT It is a common practice to employ hydrologic models for assessing alterations to streamflow as a result of anthropogenically driven changes, such as riverine, land use, and climate change. However, the ability of the models to replicate different components of the hydrograph simultaneously is not clear. Hence, this study evaluates the ability of a standard hydrologic model set-up: Variable Infiltration Capacity (VIC) hydrologic model for two headwater sub-basins in the Fraser River (Salmon and Willow), British Columbia, Canada, with climate inputs derived from observations and statistically downscaled global climate models (GCMs); to simulate six general water resource indicators (WRIs) and 32 ecologically relevant indicators of hydrologic alterations (IHA). The results show a generally good skill of the observation-driven VIC model in replicating most of the WRIs and IHAs. Although the WRIs, including annual volume, centre of timing, and seasonal flows, and the IHAs, including maximum and minimum flows, were reasonably well replicated, statistically significant differences in some of the monthly flows, number and duration of flow pulses, rise and fall rates, and reversals were noted. In the case of GCM-driven results, additional monthly, maximum, and minimum flow indicators produced statistically significant differences. A number of issues with the model input/output data, hydrologic model parametrization and structure as well as downscaling methods were identified, which lead to such discrepancies. Therefore, there is a need to exercise caution in the use of model-simulated indicators. Overall, the WRIs and IHAs can be useful tools for evaluating changes in an altered hydrologic system, provided the skill and limitations of the model in replicating these indicators are understood. © 2013 Her Majesty the Queen in Right of Canada. Hydrological Processes © 2013 John Wiley & Sons Ltd.
Hydrological Processes, 2013
ABSTRACT It is a common practice to employ hydrologic models for assessing alterations to streamf... more ABSTRACT It is a common practice to employ hydrologic models for assessing alterations to streamflow as a result of anthropogenically driven changes, such as riverine, land use, and climate change. However, the ability of the models to replicate different components of the hydrograph simultaneously is not clear. Hence, this study evaluates the ability of a standard hydrologic model set-up: Variable Infiltration Capacity (VIC) hydrologic model for two headwater sub-basins in the Fraser River (Salmon and Willow), British Columbia, Canada, with climate inputs derived from observations and statistically downscaled global climate models (GCMs); to simulate six general water resource indicators (WRIs) and 32 ecologically relevant indicators of hydrologic alterations (IHA). The results show a generally good skill of the observation-driven VIC model in replicating most of the WRIs and IHAs. Although the WRIs, including annual volume, centre of timing, and seasonal flows, and the IHAs, including maximum and minimum flows, were reasonably well replicated, statistically significant differences in some of the monthly flows, number and duration of flow pulses, rise and fall rates, and reversals were noted. In the case of GCM-driven results, additional monthly, maximum, and minimum flow indicators produced statistically significant differences. A number of issues with the model input/output data, hydrologic model parametrization and structure as well as downscaling methods were identified, which lead to such discrepancies. Therefore, there is a need to exercise caution in the use of model-simulated indicators. Overall, the WRIs and IHAs can be useful tools for evaluating changes in an altered hydrologic system, provided the skill and limitations of the model in replicating these indicators are understood. © 2013 Her Majesty the Queen in Right of Canada. Hydrological Processes © 2013 John Wiley & Sons Ltd.
The Cryosphere Discussions
Estimates of surface snow water equivalent (SWE) in alpine regions with seasonal melts are partic... more Estimates of surface snow water equivalent (SWE) in alpine regions with seasonal melts are particularly difficult in areas of high vegetation density, topographic relief and snow accumulations. These three confounding factors dominate much of the province of British Columbia (BC), Canada. An artificial neural network (ANN) was created using as predictors six gridded SWE products previously evaluated for BC: ERA-Interim/Land, GLDAS-2, MERRA, MERRA-Land, GlobSnow and ERA-Interim. Relevant spatiotemporal covariates including survey date, year, latitude, longitude, elevation and grid cell elevation differences were also included as predictors, and observations from manual snow surveys at stations located throughout BC were used as target data. Mean absolute errors (MAEs) and correlations for April surveys were found using cross validation. The ANN using the three best performing SWE products (ANN3) had the lowest mean station MAE across the entire province, improving on the performance ...
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Papers by Markus Schnorbus