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Spatiotemporal streamflow variability in a boreal landscape: Importance of landscape composition for catchment hydrological functioning
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.ORCID iD: 0000-0002-3367-5077
2016 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Avrinningens rumsliga och tidsmässiga variation i ett borealt landskap : Landskapets betydelse för avrinningsområdets hydrologiska funktion (Swedish)
Abstract [en]

The understanding of how different parts of a landscape contribute to streamflow by storing and releasing water has long been a central issue in hydrology. Knowledge about what controls streamflow dynamics across landscapes can further our understanding of how catchments store and release water, facilitate predictions for ungauged catchments, and improve the management of water quality and resources. This thesis makes use of data from the Krycklan catchment in northern Sweden. Streamflow data from 14 catchments (0.12 - 68 km2) with variable landscape characteristics such as topography, vegetation, wetland cover, glacial till soils and deeper sediment soils were used to investigate spatial patterns and controls on runoff.

The differences in specific discharge (discharge per unit catchment area) between nearby catchments were large at the annual scale, and have the same magnitude as predicted effects of a century of climate change or the observed effects of major forestry operations. This variability is important to consider when studying the effects of climate change and land use changes on streamflow, as well as for our understanding of geochemical mass balances. Streamflow from different catchments was strongly related to landscape characteristics. The distribution of wetland areas had a particularly strong influence, with an annual specific discharge 40-80% higher than catchments with high tree volume on till soils. During drier periods, catchments with deeper sediment soils at the lower elevations of Krycklan had a higher base flow compared to both forested till and wetland catchments. This pattern was reversed at high flows. The storages releasing water to streams in downstream sediment areas were able to maintain base flow for longer periods and were less influenced by evapotranspiration compared to the more superficial till and wetland systems.

The results of this thesis have led to a better understanding of the landscape wide patterns of streamflow during different seasons and time scales. The strong associations to landscape characteristics and variable spatial patterns with season and antecedent conditions form the basis for a conceptual understanding of the processes and spatial patterns that shape the heterogeneity of streamflow responses in boreal catchments.

Abstract [sv]

Hur olika delar av landskapet påverkar vattenbalansen och bidrar till avrinning har länge varit en central fråga inom hydrologin. Kunskap om vad som styr avrinningsdynamiken i ett landskap kan öka vår förståelse av hur olika delar av landskapet bidrar till avrinning, hur avrinningsområden lagrar vatten och bildar avrinning, underlätta prognoser för avrinningsområden utan vattenföringsmätningar och förbättra hanteringen av vattenkvaliteten och vattenresurser. Denna avhandling använder data från Krycklans avrinningsområde i norra Sverige. Vattenföringsdata från 14 delavrinningsområden (0.12 - 68 km2) med olika landskapskarakteristik såsom topografi, vegetation och jordarter, användes för att undersöka rumsliga mönster hos avrinningen över olika tidsperioder samt hur landskapet påverkar variabiliteten.

Skillnaderna i specifik avrinning (avrinning per areaenhet) mellan närliggande avrinningsområden var stor för årliga värden, och är i samma storleksordning som effekterna av stora skogsavverkningar samt av förutspådda effekter av det kommande seklets förväntade klimatförändringar. Denna variation är viktig att ta hänsyn till när man studerar hur klimatförändringar och ändrad markanvändning påverkar avrinningen, liksom för vår förståelse av geokemiska massbalanser. Avrinning från olika områden var starkt relaterad till deras landskapsegenskaper. Förekomsten av våtmarker hade ett särskilt starkt inflytande. Områden med en stor andel våtmarker hade 40-80% högre årlig specifik avrinning än områden med hög trädvolym på moränjordar. Under torrare perioder hade områden med djupare sedimentjordar hög avrinning jämfört med både områden med skog på morän och med våtmarker. Under höga flöden var detta mönster omvänt. De vattenlager som bidrar till avrinning i sedimentområden kan upprätthålla basflöde under längre tidsperioder och påverkas mindre av evapotranspirationen än de ytligare flödessystemen i morän och våtmarker.

Avhandlingen har givit en bättre förståelse av avrinningens rumsliga variation under olika årstider och i olika tidsskalor. Det starka sambandet mellan landskapskarakteristik och avrinningens varierande mönster under olika årstider och lagringsförhållanden utgör en grund för en begreppsmässig förståelse av de processer och rumsliga mönster som skapar heterogeniteten i flödesrespons i boreala områden.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 64 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1420
Keyword [en]
streamflow, catchment hydrology, boreal, water balance, spatiotemporal variability, landscape analysis, climate change, recession curve
National Category
Oceanography, Hydrology, Water Resources
Research subject
Hydrology
Identifiers
URN: urn:nbn:se:uu:diva-302400ISBN: 978-91-554-9680-7 (print)OAI: oai:DiVA.org:uu-302400DiVA: diva2:957781
Public defence
2016-10-21, Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2016-09-29 Created: 2016-09-01 Last updated: 2016-10-11
List of papers
1. The assumption of uniform specific discharge: unsafe at Any time?
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2016 (English)In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 0, no 21, 3978-3988 p.Article in journal (Refereed) Published
Abstract [en]

Nearby catchments in the same landscape are often assumed to have similar specific discharge (runoff per unit catchment area). Five years of streamflow from 14 nested catchments in a 68km(2) landscape was used to test this assumption, with the hypothesis that the spatial variability in specific discharge is smaller than the uncertainties in the measurement. The median spatial variability of specific discharge, defined as subcatchment deviation from the catchment outlet, was 33% at the daily scale. This declined to 24% at a monthly scale and 19% at an annual scale. These specific discharge differences are on the same order of magnitude as predicted for major land-use conversions or a century of climate change. Spatial variability remained when considering uncertainties in specific discharge, and systematic seasonal patterns in specific discharge variation further provide confidence that these differences are more than just errors in the analysis of catchment area, rainfall variability or gauging. Assuming similar specific discharge in nearby catchments can thus lead to spurious conclusions about the effects of disturbance on hydrological and biogeochemical processes.

Keyword
specific discharge; streamflow; spatio-temporal variability; catchment hydrology; boreal
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:uu:diva-292672 (URN)10.1002/hyp.10877 (DOI)000385434400016 ()
Funder
Swedish Research CouncilSwedish Research Council FormasThe Kempe Foundations
Available from: 2016-05-06 Created: 2016-05-06 Last updated: 2017-11-30Bibliographically approved
2. Landscape controls on spatiotemporal discharge variability in a boreal catchment
Open this publication in new window or tab >>Landscape controls on spatiotemporal discharge variability in a boreal catchment
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2016 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, no 8, 6541-6556 p.Article in journal (Refereed) Published
Abstract [en]

Improving the understanding of how stream flow dynamics are influenced by landscape characteristics, such as soils, vegetation and terrain, is a central endeavor of catchment hydrology. Here we investigate how spatial variability in stream flow is related to landscape characteristics using specific discharge time series from 14 partly nested subcatchments in the Krycklan basin (0.12 - 68 km(2)). Multivariate principal component analyses combined with univariate analyses showed that while variability in landscape characteristics and specific discharge were strongly related, the spatial patterns varied with season and wetness conditions. During spring snowmelt and at the annual scale, specific discharge was positively related to the sum of wetland and lake area. During summer, when flows are lowest, specific discharge was negatively related to catchment tree volume, but positively related to deeper sediment deposits and catchment area. The results indicate how more densely forested areas on till soils become relatively drier during summer months, while wet areas and deeper sediment soils maintain a higher summer base flow. Annual and seasonal differences in specific discharge can therefore be explained to a large extent by expected variability in evapotranspiration fluxes and snow accumulation. These analyses provide an organizing principle for how specific discharge varies spatially across the boreal landscape, and how this variation is manifested for different wetness conditions, seasons and time scales.

Keyword
streamflow, catchment hydrology, spatiotemporal variability, boreal, landscape analysis
National Category
Oceanography, Hydrology, Water Resources
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-302397 (URN)10.1002/2016WR019186 (DOI)000383684400047 ()
Funder
Swedish Research CouncilSwedish Research Council FormasThe Kempe Foundations
Available from: 2016-09-03 Created: 2016-09-01 Last updated: 2017-11-21Bibliographically approved
3. Hydrological response to changing climate conditions: Spatial streamflow variability in the boreal region
Open this publication in new window or tab >>Hydrological response to changing climate conditions: Spatial streamflow variability in the boreal region
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2015 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51Article in journal (Refereed) Published
Abstract [en]

In this paper we combined a multi-model ensemble based on 15 regional climate models with a multi-catchment approach to explore the hydrologic sensitivity of 14 neighboring and rather similar catchments to changing climate conditions. Current (1982-2010) and future (2062-2090) streamflow was simulated with the HBV model. A diagnostic approach was used, which considered major behavioral catchment functions by using hydrologically relevant signatures related to overall water balance, flow duration curves and hydrograph attributes. Projected increases in temperature and precipitation resulted in increased total available streamflow, with lower spring and summer flows, but substantially higher winter streamflow. Furthermore, significant changes in flow durations with lower chances of both high and low flows can be expected in boreal Sweden in the future. This overall trend in projected streamflow pattern changes was comparable among the analyzed catchments but the magnitude of change differed considerably. This suggests that catchments belonging to the same region can show distinctly different degrees of hydrological responses to the same external climate change signal. We reason that differences in spatially distributed physical catchment properties within catchments are not only of great importance for current streamflow behavior, but also play a major role in the sensitivity of catchments to changing climate conditions.

Keyword
Climate Change, Hydrology, Streamflow, Sweden, HBV
National Category
Oceanography, Hydrology, Water Resources Climate Research
Research subject
Earth Science with specialization in Environmental Analysis; Earth Science with specialization in Physical Geography; Hydrology
Identifiers
urn:nbn:se:uu:diva-266270 (URN)10.1002/2015WR017337 (DOI)000368421500003 ()
Funder
Swedish Research Council FormasMistra - The Swedish Foundation for Strategic Environmental ResearchThe Kempe Foundations
Available from: 2015-11-05 Created: 2015-11-05 Last updated: 2017-12-01Bibliographically approved
4. The role of catchment physiography, storage and evapotranspiration on variability in streamflow recessions
Open this publication in new window or tab >>The role of catchment physiography, storage and evapotranspiration on variability in streamflow recessions
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(English)Manuscript (preprint) (Other academic)
National Category
Oceanography, Hydrology, Water Resources
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-302399 (URN)
External cooperation:
Available from: 2016-09-03 Created: 2016-09-01 Last updated: 2016-09-04

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Karlsen, Reinert Huseby

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