Over the course of the last weeks both Italian and international press reported on the current drought situation in Italy (the Guardian, die Zeit, la Repubblica). The spring of 2017 was one of the driest, in Italy, in about 60 years with rainfall totals 80% below normal, in some regions. The effects of this situation on agricultural production (especially dairy, tomatoes, and wine) are already starting to show now. The Italian farmers’ lobby Coldiretti are estimating damages of up to €2bn, for this year (link to the report). In some areas, even the supply of drinking water is getting short. In Rome, for example, the mayor has restricted the use of water for the filling of swimming pools or the cleaning of cars and motorbikes.
Besides rainfall, the soil water content (or soil moisture content), defined as the quantity of water held in the soil against gravity, is one important indicator for drought. The knowledge of this parameter plays a role in the observation of the climate system and the hydrological cycle. In the case of agriculture, the soil moisture content is directly related to the availability of water for plants.
The soil moisture content can be measured from space using satellite observations of the Earth in the microwave spectrum. In the framework of Eurac Research’s SAO initiative, we developed an approach that allows the mapping of soil moisture, based on data from the Copernicus satellite Sentinel-1, with high spatial resolution (for a detailed description of the retrieval algorithm see here).
Figure 1: The temporal evolution of the spatially averaged soil moisture (blue line) and precipitation (green line). The red vertical lines indicate June 2015, 2016, and 2017, respectively.
Our data allows us to take a closer look at the situation in our region, the province of South Tyrol in Italy. The figure above shows the temporal evolution of the average soil moisture content over the course of the last three years. While the Sentinel-1 time-series is still too short to assess the magnitude of a drought, compared to the long term averages, we clearly see how it responds to shortage of rainfall this spring. The real strength of the satellite based methods is the potential of spatially continuous mapping, which allows us to gain better understanding of the spatial variations and the development of local phenomena. The next figure contains three maps showing monthly averages for June 2015, 2016, and 2017. They demonstrate how highly variable the soil moisture content can be (white pixels correspond to “no-data” areas), in all three maps we can see local patterns of very low and very high values at the same time but, also, they do clearly show that June 2017 is overall drier than 2015 and 2016.
Figure 2: The spatial distribution of the soil moisture index for June 2015, 2016, and 2017. Credit: Contains modified Copernicus Sentinel data (2015-2017)/ESA