As we all know, remote sensing means are appropriate for examining problems on a large scale and in areas that are difficultly accessible. Also, remote sensing data provide area-wide information on a certain question and therefore deliver complete (area-wide) solutions.

Droughts are natural hazards not solely caused by precipitation deficits, but also may be induced by humans when elevated amounts of surface water are used for human activities (tourism, industry and agriculture) or by general atmospheric circulation patterns, which act as top (most important) regulators on local weather occurrences. In any case, droughts imply a (considerable) harm for society reducing crop harvests and production of electricity (water power). During the last half a year I tried to find out the potential of predicting local drought events by using information of such macro (climatic) variables in advance on the one hand and remote sensing data on the other hand. The Iberian Peninsula is frequently hit by droughts and at the same time highly influenced by the atmospheric circulation pattern of North Atlantic Oscillation (NAO – difference between sea level pressure around the Azores and Iceland). Researchers found out that especially precipitation patterns in Iberia alternate with a modification of NAO index (NAO is specified by a certain value, which can be positive or negative). The purpose of the study was to investigate if droughts in Iberia are influenced by NAO and under which NAO index they are most likely to occur in which part of Iberia. I used MODIS satellite products to calculate an established drought index, the Vegetation Temperature Condition Index (VTCI), and in this way directly obtained information on droughts.

Indeed, droughts during spring and summer as the most important seasons for plant growth are spatially influenced by the NAO winter index (D,J,F,M). The information at a local scale can be useful for developing an outlook system for soil moisture conditions especially for spring months, which would be of great interest for agriculture in terms of drought management. The map at the bottom shows the correlation between NAO and VTCI in April and June.

The maps exemplify the correlation between VTCI and NAO for one month in spring (April) and summer (June). The dark red areas indicate highly negatively correlated areas between VTCI and NAO, blue areas delineate positively correlated areas. Interestingly the pattern flips between April and June and remains similar during the other summer months. Source: Stefan Mühlbauer

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