Drought brings water shortage to parts of Italy

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Following an extremely dry spring causing a drought, parts of Italy suffered from water shortages in 2017.

Drought brings water shortage to parts of Italy
Date & Time
Period June–July 2016 and 2017
Satellites
Metop-A, Meteosat-10
Instruments
ASCAT, SEVIRI
Channels/Products
ASCAT Soil Moisture Index, Leaf Area Index, monthly minimum Natural Colour RGB

By Jose Prieto and Sancha Lancaster (EUMETSAT)

Spring 2017 in parts of Italy was the driest for 60 years, with rainfall 80% below average. Rainfall in the first six months of the year was down 33%.

In July it was reported that the historic fountains in Saint Peter’s Square at the Vatican, Rome, were switched off and 10 regions had declared a state of emergency due to the prolonged drought.

The level of the Lago di Bracciano (the main water resource for Rome) was reported (La Stampa, in Italian) to be well below minimum critical value, at least 165 cm below normal.

 
Figure 2: Soil moisture mosaic as retrieved from Metop-B ASCAT for 1st and 2nd August 2017, evening northbound Metop passes. The relative moisture values indicate a very low water reserve in the soil, compared with a humid central Europe.

The EUMETSAT Satellite application facilities (SAF) take raw satellite information and generate products on different fields of societal benefit, including energy, water and climate.

In this case we use examples from the SAF on Support to Operational Hydrology and Water Management (H SAF) and the Land Surface Analysis SAF (LSA SAF)

The H SAF uses the backscatter data from ASCAT to produce an estimate of the surface soil moisture. Radar backscatter values are scaled between 0% (dry soil) and 100% (wet soil, saturated with water).

The obtained relative soil moisture estimates represent the moisture in the topmost five centimetres of the soil.

In Figure 2 it can be seen that the soil moisture at the end of July 2017 was poor, compared to 2016.

The central part of Italy seems most affected by evaporation and vegetation drying due to the hot conditions.

The soil humidity (7 to 28 cm under the surface) in Europe on 3 August 2017, as computed from models, is more extreme in parts of Eastern Europe and Spain than in Italy, though.

The degree of saturation is influenced by recent precipitation and is not informative in the long run.

The values spike after precipitation events, so the choice of a similar precipitation history is a needed step in comparisons.

Figure 3 is the comparison of the Land SAF's leaf area index from earlier in the year (start of June), prior to the summer dry weather and current vegetation wilting in hot places.

This second index is less sensitive to precipitation events and a better proxy for accumulated humidity. Here we can see low values in 2017 in the central Italian region of Lazio (left hand image), which might explain the water restrictions under consideration.

Leaf index comparison
Image from 1 June 2016 Image from 1 June 2017
Figure 3: Leaf area index on 1 June of 2016 and 2017. As a vegetation index, the readings are more indicative of long term precipitation in the area than volatile readings of soil moisture. Scale from 0 (0%) to 10 (100%).

Figure 4 compares an image obtained from a July summary on 2016 and 2017 for solar information. The Meteosat-10 solar channels at 0.6, 0.8 and 1.6 µm provide an excellent monitoring tool for the soil. Gaps were covered to provide the vegetation maximum during the month.

Sardegna, Sicily, Puglia and Lazio appear much drier in July than one year ago. Lazio shows less vegetation growth too, although to a lesser extent.

Solar comparison
Summary for July 2016 Summary for July 2017
Figure 4: After declouding the scenes, a monthly summary of the soil albedo emerges from solar composites. Pink indicates soil dryness, bright yellowish marks vegetation growth.

July is typically dry in Italy, as can be seen in the Meteosat-10 Natural Colour RGB animation, 1 July 2016 11:57 UTC –30 July 2017 11:57 UTC (MP4, 5 MB), which encompasses two successive months of July (2016/2017), where very short episodes of rain can be spotted.

 
 

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