Understanding soil moisture in the Northern Areas: Toward an integrated representation of the Arctic Hydrological Cycle

Climate research shows that the northern latitudes could face an increase in risk of extreme weather events in the future, such as heavy precipitation and droughts. The PhD-student has in this project applied data assimilation to combine satellite observations and model derived soil moisture estimates, with the potential to improve numerical weather prediction as well as forecast of flood and drought. By combining information of soil moisture from satellites and model data, we are able to reduce the uncertainty related to the two datasets. This is done by exploiting what we know about the uncertainty in remote sensing and modelling of soil moisture, in a framework called data assimilation. This could potentially improve our estimates of soil moisture in unobserved parts of the modelling framework, e.g., root-zone soil moisture. Soil moisture is defined as the amount of water in the unsaturated zone of the soil, i.e., from the surface to around 2 m depth. Even though soil moisture only constitutes a small fraction of the total water cycle it plays an important role in for example water available for plants, numerical weather prediction, climate, flood and drought. Thus, soil moisture is an important variable to monitor. There are several approaches to monitor soil moisture, for example, through in situ stations, satellites or models. The PhD-student has, among other things, applied satellite derived soil moisture observations from the European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) satellite to monitor the Nordic drought 2018. The results from this project opens for opportunities to use satellite data directly to monitor drought over northern latitudes, or indirectly through data assimilation of satellite derived soil moisture.

The PhD-student is successfully trained in EO and land DA, resulting in 2 peer-reviewed journal articles, 1 manuscript in preparation and a PhD-thesis, which has been accepted for defense. The 3 articles investigate the error characteristics of SMOS soil moisture observations and land surface models. By applying DA soil moisture information on regional scale has been improved. We have used satellite observations of surface soil moisture and land surface models to map and monitor the 2018 drought in Scandinavia. This study demonstrates the benefits of land surface mapping over northern latitudes. The links between Norwegian research institutions and the international community were strengthen through a three months visit to Princeton University, USA and a shorter visit to KU Leuven, Belgium. This project has provided the foundation for an application to the NRC Mobility Grant, demonstrating transfer of information and knowledge from this project to future projects on coupled DA.

This project funds a PhD studentship to use SMOS and other satellite soil moisture observations to build a novel multi-year data resource that will provide information for land surface mapping of Northern Areas. It will augment SMOS soil moisture data with satellite soil moisture datasets compiled under the Soil Moisture ESA Climate Change Initiative (ESA-CCI): e.g., ASCAT, AMSR-E. The project will use data assimilation (DA) to improve spatio-temporal information provided by satellite soil moisture datasets and provide a soil moisture analysis for Northern Areas in line with user needs for land surface mapping (spatial resolution, c. 5 km; temporal resolution, c. 3 hours). This analysis will incorporate SMOS/ASCAT soil moisture data from Jan 2010 to the present; AMSR-E soil moisture data from Jan 2010 to Oct 2011; and other available data. The DA system will form the basis for an integrated coupled atmosphere-land-ocean DA system to study the Arctic Hydrological Cycle. The student will use cutting-edge DA ideas/techniques. He/she will strongly benefit from being in an experienced, dynamic, well-resourced and well-managed research group at NILU, with access to a state-of-the-art land DA set-up, and strong national/international links to key actors in the hydrological cycle. The project is relevant to the proposal call - it involves: PhD training; validation, SMOS soil moisture observations; use of satellite soil moisture observations for land surface mapping, with potential for climate monitoring, monitoring of environmental threats; networking among Norwegian institutions (NERSC/NILU/UiB), including the NORDFORSK CoE in DA; strong links with international institutions and projects (Soil Moisture/Ocean Colour ESA CCIs). The project is strongly aligned with NFR strategy document "Visjon for 2015-Rom for forskning", notably: (i) research from space; (ii) development of novel algorithms; (iii) key issues for Norway; and (iv) government departments in Norway.