Water / Hydrosphere

Mapping and monitoring of sea surface temperatures

Sea surface temperatures have a large influence on climate and weather. For example, the periodical warming of a wide swath of the Pacific Ocean is a hallmark of the climate pattern El Niño, which changes rainfall patterns around the globe, causing heavy rainfall in the southern United States and severe drought in Australia, Indonesia, and southern Asia. With remote sensing you can not only monitor the spatial and temporal variations of sea temperatures on a global scale but also on smaller scales, such as the fair degree of temperature variation in the waters of the Mediterranean, which is generally significantly warmer as you travel east and there is around 10°C range between winter and summer high and lows.

Spatio-temporal variations of sea surface temperature in the Mediterranean.
Spatio-temporal variations of sea surface temperature in the Mediterranean. (Image: UZH/NPOC/P. Jörg)


Assessment of snow properties and dynamics of snow coverage

Snow is one of the most relevant natural water resources present in nature. It stores water in winter and releases it in spring during the melting season. Monitoring snow cover and its variability is thus of great importance for a proactive management of water-resources. Of particular interest is the identification of snowmelt processes, which could significantly support water administration, flood prediction and prevention. Present operational satellite systems are not only limited to determining the area of snow cover but are also suitable to derive information about snow physical parameters, such as the snow water, to a certain extent.

Average duration of snow coverage between 2005 and 2016 with bright colors representing short term snow coverage and darker colors representing longer coverage including glaciers.
Average duration of snow coverage between 2005 and 2016 with bright colors representing short term snow coverage and darker colors representing longer coverage including glaciers. (Image: UZH/NPOC/P. Jörg)

Measuring of water transparency

Water transparency can be affected by the colour of the water, algae, and suspended sediments but can also be an indicator of the impact of human activity on the land surrounding the lake. For example, transparency can be affected by the amount of plant nutrients coming into the lake from sources such as sewage treatment plants, septic tanks, and lawn and agricultural fertilizer. Suspended sediments often come from sources such as resuspension from the lake bottom, construction sites, agricultural fields, and urban storm runoff. With remote sensing, you can measure, among other things, optical properties of the water which allows getting comparable results to the traditionally applied in-situ Secchi depth measurements, which is related to water turbidity.

Calculation of the Secchi depth for open water bodies in Switzerland based on optical remote sensing data.
Calculation of the Secchi depth for open water bodies in Switzerland based on optical remote sensing data. (Image: UZH/NPOC/D. Fawcett)


Observation of coupled precipitation-vegetation variability

With climate change, alterations of the seasonal distribution of precipitation patterns and a higher frequency of extreme events are expected. Vegetation dynamics are likely to respond to these changes and thus ecosystem services will be affected. Recent studies indicate that water availability is the most dominant factor driving vegetation globally: about 61% of the vegetated surface was primarily water-limited during 1981–2010. In this context, Earth Observation contributes greatly to an improved understanding of vegetation sensitivity to precipitation anomalies and corresponding temporal reaction patterns at regional scale.

Interrelationship between rainfall anomalies (top) and the state of vegetation in Eastern Africa for the reference period June 2010-June 2016 and the comparison period June 2016-June 2017.
Interrelationship between rainfall anomalies (top) and the state of vegetation in Eastern Africa for the reference period June 2010-June 2016 and the comparison period June 2016-June 2017. (Image: UZH/NPOC/P. Jörg)