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Modeling long-term variability and change of soil moisture and groundwater level - from catchment to global scale
Stockholm University, Faculty of Science, Department of Physical Geography.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The water stored in and flowing through the subsurface is fundamental for sustaining human activities and needs, feeding water and its constituents to surface water bodies and supporting the functioning of their ecosystems. Quantifying the changes that affect the subsurface water is crucial for our understanding of its dynamics and changes driven by climate change and other changes in the landscape, such as in land-use and water-use. It is inherently difficult to directly measure soil moisture and groundwater levels over large spatial scales and long times. Models are therefore needed to capture the soil moisture and groundwater level dynamics over such large spatiotemporal scales.

This thesis develops a modeling framework that allows for long-term catchment-scale screening of soil moisture and groundwater level changes. The novelty in this development resides in an explicit link drawn between catchment-scale hydroclimatic and soil hydraulics conditions, using observed runoff data as an approximation of soil water flux and accounting for the effects of snow storage-melting dynamics on that flux. Both past and future relative changes can be assessed by use of this modeling framework, with future change projections based on common climate model outputs. By direct model-observation comparison, the thesis shows that the developed modeling framework can reproduce the temporal variability of large-scale changes in soil water storage, as obtained from the GRACE satellite product, for most of 25 large study catchments around the world. Also compared with locally measured soil water content and groundwater level in 10 U.S. catchments, the modeling approach can reasonably well reproduce relative seasonal fluctuations around long-term average values.

The developed modeling framework is further used to project soil moisture changes due to expected future climate change for 81 catchments around the world. The future soil moisture changes depend on the considered radiative forcing scenario (RCP) but are overall large for the occurrence frequency of dry and wet events and the inter-annual variability of seasonal soil moisture. These changes tend to be higher for the dry events and the dry season, respectively, than for the corresponding wet quantities, indicating increased drought risk for some parts of the world.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography, Stockholm University , 2016. , 36 p.
Series
Dissertations from the Department of Physical Geography, ISSN 1653-7211 ; 57
Keyword [en]
hydrology, physically-based model, groundwater, soil moisture
National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-128322ISBN: 978-91-7649-387-8OAI: oai:DiVA.org:su-128322DiVA: diva2:950832
Public defence
2016-09-22, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2016-08-30 Created: 2016-03-23 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Screening variability and change of soil moisture under wide-ranging climate conditions: Snow dynamics effects
Open this publication in new window or tab >>Screening variability and change of soil moisture under wide-ranging climate conditions: Snow dynamics effects
2015 (English)In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, 6-16 p.Article in journal (Refereed) Published
Abstract [en]

Soil moisture influences and is influenced by water, climate, and ecosystem conditions, affecting associated ecosystem services in the landscape. This paper couples snow storage-melting dynamics with an analytical modeling approach to screening basin-scale, long-term soil moisture variability and change in a changing climate. This coupling enables assessment of both spatial differences and temporal changes across a wide range of hydro-climatic conditions. Model application is exemplified for two major Swedish hydrological basins, Norrstrom and Pitealven. These are located along a steep temperature gradient and have experienced different hydro-climatic changes over the time period of study, 1950-2009. Spatially, average intra-annual variability of soil moisture differs considerably between the basins due to their temperature-related differences in snow dynamics. With regard to temporal change, the long-term average state and intra-annual variability of soil moisture have not changed much, while inter-annual variability has changed considerably in response to hydro-climatic changes experienced so far in each basin.

Keyword
Soil moisture, Groundwater, Snow dynamics, Climate change, Landscape scale, Hydrological basin
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-114257 (URN)10.1007/s13280-014-0583-y (DOI)000347680100002 ()25576276 (PubMedID)
Note

AuthorCount:2;

Available from: 2015-03-26 Created: 2015-02-25 Last updated: 2016-08-03Bibliographically approved
2. Screening long-term variability and change of soil moisture in a changing climate
Open this publication in new window or tab >>Screening long-term variability and change of soil moisture in a changing climate
2014 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 516, 131-139 p.Article in journal (Refereed) Published
Abstract [en]

Soil moisture is an essential component of water variability and change in the landscape. This paper develops a conceptual and analytical framework for linking hydro-climatic change at the surface and soil-groundwater conditions in the subsurface, and quantifying long-term development of soil moisture statistics in a changing climate. Soil moisture is evaluated both in the unsaturated zone and over a fixed soil depth that may also include a variable groundwater table. Long-term variability and change of soil moisture are assessed for a hydro-climatic observation record that extends over the whole 20th century in a major Swedish drainage basin. Frequencies of particularly dry and wet soil moisture events are investigated for different 20-year climatic periods. Results show major increase in the frequency of dry events from the beginning to the end of the 20th century. This indicates increased risk for hydrological and agricultural drought even though the risk for meteorological drought, in terms of precipitation, has decreased in the region. The developed quantification framework can also be used to screen future scenarios of soil moisture change under projected climate change.

Keyword
Soil moisture, Groundwater table, Climate change, Hydro-climate, Drought
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-106739 (URN)10.1016/j.jhydrol.2014.01.059 (DOI)000339036100012 ()
Note

AuthorCount:2;

Available from: 2014-08-20 Created: 2014-08-19 Last updated: 2016-08-03Bibliographically approved
3. Data-model comparison of temporal variability in long-term time series of large-scale soil moisture
Open this publication in new window or tab >>Data-model comparison of temporal variability in long-term time series of large-scale soil moisture
2016 (English)In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996Article in journal (Refereed) Epub ahead of print
Abstract [en]

Soil moisture is at the heart of many processes connected to water cycle, climate, ecosystem and societal conditions. This paper investigates the ability of a relatively simple analytical soil-moisture model to reproduce temporal variability dynamics in long-term data series for: (i) remotely sensed large-scale water storage change in twenty-five large catchments around the world, and (ii) measured soil water content and groundwater level in individual stations within ten smaller catchments across the United States. The model-data comparison for large-scale water storage change (i) shows good model ability to reproduce the observed temporal variability around long-term average conditions in most of the large study catchments. Also the model comparison with locally measured data for soil water content and groundwater level in the smaller U.S. catchments (ii) shows good representation of relative seasonal and longer-term fluctuations and their timings and frequencies. Overall, the model results tend to underestimate rather than exaggerate the range of temporal soil moisture fluctuations and storage changes. The model synthesis of large-scale hydro-climatic data is based on fundamental catchment-scale water balance and is as such useful for identifying flux imbalance biases in the hydro-climatic data series that are used as model inputs.

National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-132250 (URN)10.1002/2016JD025209 (DOI)
Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-14
4. Worldwide soil moisture changes driven by future hydro-climatic change scenarios
Open this publication in new window or tab >>Worldwide soil moisture changes driven by future hydro-climatic change scenarios
2016 (English)In: Hydrology and Earth System Sciences Discussions, ISSN 1812-2108, E-ISSN 1812-2116Article in journal (Refereed) Epub ahead of print
Abstract [en]

Soil moisture is a key variable in hydrology, ecology, and climate change science. It is also of primary importance for the agricultural and water resource sectors of society. This paper investigates how hydro-climatic changes, projected by 14 CMIP5 models and for different radiative forcing (RCP) scenarios to occur from 2006-2025 to 2080-2099, may affect different soil moisture aspects in 81 large catchments worldwide. Overall, for investigated changes in dry/wet event occurrence and in average value and inter-annual variability of seasonal water content, different RCP scenarios imply opposite directions of change in around half or more of the study catchments. Regardless of RCP scenario, the greatest projected changes are found for the inter-annual variability of seasonal soil water content. Especially for the dry-season water content, large increases in inter-annual variability emerge for several large catchments over the world; the considered RCP scenario determines precisely which these catchments are.

National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-132249 (URN)10.5194/hess-2016-165 (DOI)
Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-14

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