Precipitation variability and its relationship to hydrologic variability in Alberta

Mwale, Davison; Gan, Thian Yew; Devito, K. J.; Mendoza, Carl; Silins, U.; Petrone, Richard M.

doi:10.1002/hyp.7415

Cited by 56 publications

(52 citation statements)

References 25 publications

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“…The growing season of our study region is also relatively cool and wet (Environment Canada 2008;Mwale et al 2009). Although temperatures have risen significantly in recent decades and drought severity has increased in some parts of Alberta, there was no discernable increase in the occurrence or intensity of drought events in the foothills of west-central Alberta during the twentieth century (Shen et al 2003;Mwale et al 2009). Therefore, the current trend towards warmer weather may not yet be causing sufficient water deficits during the growing season to affect the mortality rates of established trees (DBH > 7 cm) in our study area.…”

Section: Discussionmentioning

confidence: 99%

Long-term trends in tree mortality rates in the Alberta foothills are driven by stand development

Thorpe

Daniels

2012

Can. J. For. Res.

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Tree mortality is a critical driver of stand dynamics, influencing forest structure, composition, and capacity for ecosystem service provision. In recent years, tree mortality has been gaining attention as dramatic occurrences of forest dieoff have been linked to climate change. Using permanent sample plot data, we examined tree mortality rates in mature forests in west-central Alberta from 1956 to 2007. We quantified mortality risk at an individual-tree level as a function of size, local competition, and calendar year, a proxy for increasing temperature, and used maximum likelihood methods to estimate species-specific model parameters. Tree size and local competition were both important predictors of mortality risk. However, once these factors were included in our model, no additional variation could be attributed to calendar year, indicating that the trend of increasing tree mortality over time found in our raw data is primarily a result of stand development processes. This finding is supported by the changes in forest structure and composition that we documented over the study period. Stands generally increased in basal area and stem density, and lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson) declined in abundance relative to the more shade-tolerant black spruce (Picea mariana (Mill.) B.S.P.) and white spruce (Picea glauca (Moench) Voss). Our results indicate that warming-related changes did not affect background tree mortality rates in mature forests in the Alberta foothills over the study period. These results also provide critical information for future studies of forest dynamics in the region.Résumé : La mortalité des arbres est un facteur important de la dynamique des peuplements qui a un impact sur la structure, la composition et la capacité des peuplements à préserver l'écosystème forestier. Au cours des dernières années, la mortalité a fait l'objet d'une attention croissante à cause d'épisodes de mortalité massive liés aux changements climatiques. En utilisant des données de placettes échantillons permanentes, nous avons étudié le taux de mortalité des arbres dans les forêts matures du centre-ouest de l'Alberta de 1956 à 2007. Nous avons quantifié le risque de mortalité à l'échelle de l'arbre en fonction de la taille, de la compétition locale et de l'année civile, qui reflète l'augmentation des températures, et nous avons utilisé des méthodes de maximum de vraisemblance pour estimer les paramètres de modèles propres à chaque espèce. La taille des arbres et la compétition locale étaient deux prédicteurs importants du risque de mortalité. Toutefois, lorsque ces facteurs étaient inclus dans le modèle, aucune variation additionnelle ne pouvait être expliquée par l'année civile, ce qui indique que la tendance à l'augmentation de la mortalité avec le temps observée dans nos données brutes est surtout produite par les processus de développement du peuplement. Ce résultat est appuyé par les changements de structure et de composition forestière observés au cours de la période d'étude. La su...

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Section: Discussionmentioning

confidence: 99%

Long-term trends in tree mortality rates in the Alberta foothills are driven by stand development

Thorpe

Daniels

2012

Can. J. For. Res.

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“…P data were interpolated within watersheds using an inverse distance weighting approach, which maintains the integrity of point locations but also provides continuous estimates of climate variables throughout the full extent of the basin. The 22‐year period includes a range of hydro‐climatic patterns including wet, dry, and normal conditions for this region (Mwale et al, ).…”

Section: Methodsmentioning

confidence: 99%

“…The climate within the low‐relief central mixedwood (CMw) natural subregion is subhumid, with precipitation (P) closely balancing potential evapotranspiration (PET), whereas the upper and lower foothills (herein LFh) natural subregions receive greater P partly through orographic effects (Devito et al, ). Maximum PET coincides with maximum P during the summer months, thereby limiting excess water availability during most years, especially within the CMw natural subregion (Marshall, Schut, & Ballard, ), whereas occasional wet years occur every 10–12 years, moderating lengthy water deficit periods (Devito, Creed, & Fraser, ; Mwale et al, ).…”

Section: Introductionmentioning

confidence: 99%

Remote sensing of ecosystem trajectories as a proxy indicator for watershed water balance

et al. 2018

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Ecosystem trajectories are inextricably linked to hydrology; however, water availability is not easily observed within the landscape. The response of vegetation to soil water availability may provide an indicator of local hydrology and the resilience or sensitivity of ecosystems to long‐term changes in water balance. In this study, vegetation trajectories derived from Landsat Modified Soil Adjusted Vegetation Index over a 22‐year period are used as an indicator of spatio‐temporal changes of watershed water balance and surface water storage within 6 proximal watersheds of the Boreal Plains ecozone of Alberta, Canada. The interactions between hydrology, topography, geology, and land cover type are examined as they relate to vegetation change. In this study, we find that run‐off ratio (run‐off/precipitation) is greater within watersheds with greater variability of relief, compared within subhumid, wetland‐dominated watersheds (average = 0.35, 0.20, respectively), which experience lagged run‐off response. A 2‐year drought had a greater impact on vegetation trajectories within variable relief watersheds containing a high proportion of coarse‐grain surficial geology, compared with peatland‐dominated watersheds. The drought extended for an additional 1 to 2 years within 3 subhumid watersheds, reducing watershed run‐off to less than 50 mm per water year (November to October) in 2 watersheds. However, proportional area of decline of Modified Soil Adjusted Vegetation Index was significantly less within these watersheds. The results of this study indicate that wetlands play an important role for local water balance and ecosystem maintenance during periods of water stress and should be considered within land use planning and reclamation strategies of the Boreal Plains.

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“…Because selected climate indices appear to be interrelated at several time scales [ Gan et al ., ; Ng and Chan , , ], the stand‐alone relationship between a climate index series and the MMDP time series was further studied by removing the effect of another climate index using the PWC [ Mihanović et al ., ]. WEOF analysis [ Gan et al ., ; Mwale et al ., ; Jiang et al ., ] was used to reduce the dimensionality of SAWP time series at multilocations to some orthogonal PCs that can explain the majority of the variability in regional SAWP.…”

Section: Methodsmentioning

confidence: 99%

Wavelet analysis of precipitation extremes over Canadian ecoregions and teleconnections to large‐scale climate anomalies

2016

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To detect significant interannual and interdecadal oscillations and their teleconnections to large‐scale climate anomalies such as El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and North Atlantic Oscillation (NAO), monthly and seasonal maximum daily precipitation (MMDP and SMDP) from 131 stations across Canada were analyzed by using variants of wavelet analysis. Interannual (1–8 years) oscillations were found to be more significant than interdecadal (8–30 years) oscillations for all selected stations, and the oscillations are both spatial and time‐dependent. Similarly, the significant wavelet coherence and the phase difference between leading principal components of monthly precipitation extremes and climate indices were highly variable in time and in periodicity, and a single climate index explains less than 40% of the total variability. Partial wavelet coherence analysis shows that both ENSO and PDO modulated the interannual variability and PDO modulated the interdecadal variability, of MMDP over Canada. NAO is correlated with the western MMDP at interdecadal scale and the eastern MMDP at interannual scale. The composite analysis shows that precipitation extremes at about three fourths of the stations have been significantly influenced by ENSO and PDO patterns, while about one half of the stations by the NAO patterns. The magnitude of SMDP in extreme El Niño years, and extreme PDO event of positive phase, was mostly lower (higher) over the Canadian Prairies in summer and winter (spring and autumn) than in extreme La Niña years. Overall, the degree of influence of large‐scale climate patterns on Canadian precipitation extremes varies by season and by region.

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Precipitation variability and its relationship to hydrologic variability in Alberta

Cited by 56 publications

References 25 publications

Long-term trends in tree mortality rates in the Alberta foothills are driven by stand development

Long-term trends in tree mortality rates in the Alberta foothills are driven by stand development

Remote sensing of ecosystem trajectories as a proxy indicator for watershed water balance

Wavelet analysis of precipitation extremes over Canadian ecoregions and teleconnections to large‐scale climate anomalies

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