News Drought
'The term drought is very complex'
"The term drought is more complex than people think," said Richard de Jeu, founder and technical director of space technology company VanderSat. "For most people it's a lack of rain, but there's more to it." It is currently 30% drier than average, the company calculated based on its own satellite images.
VanderSat calculated last year it was 20% drier than normal in the Netherlands at the end of June. Founder and CTO Richard de Jeu called it the worst drought in 15 years. However, enough rain fell shortly afterwards, so 2017 didn't end so dry after all.
Drought just gets
We are more than 1 week later this year and again it is very dry. "Compared to the past 15 years, the drought of 2018 is one of the worst in the Netherlands," said De Jeu. "In 2013 and 2017 it was also quite dry. It seems to be getting more and more normal." Based on its own satellite data, the company calculated that it will be 30% drier than normal at the beginning of July.
Several American, European and Japanese satellites are used by the company to measure how dry it is worldwide. Not only the precipitation is considered, but also the influence of the soil type and the available groundwater is taken into account, as well as the temperature of the soil and the crop.
groundwater
Director of Water Management Jaap Schellekens: "Which point of view do you use when assessing drought? Are precipitation or evaporation looking purely at it? However, the soil type and availability of water for irrigation also play a role. The satellite images show the influence of the groundwater. The Groene Hart is a good example of this; despite little precipitation, it is not dry there, because there is still enough water in the soil."
"The KNMI map, which shows the continuous potential precipitation surplus, looks at the radiation for evaporation. If there is no water available, it will not evaporate. This determines the real drought. If irrigated on a large scale, we see This is reflected in the images. This is not (yet) the case for each plot. Moreover, measurements are taken at night, so that the effect is somewhat leveled out," says Schellekens.
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Left: the average for June 2018. - Right: versus the previous 5 years.
VanderSat made a map of the average soil moisture status in the month of June. The influence of the groundwater is clearly visible on this. However, if the month is compared with the previous 5 years, the picture is more even. The dry Achterhoek and the southeast of North Brabant remain clearly visible as bone-dry areas. The influence of evaporation by different crops is relatively uniform.
Huge differences
The claim that it is 30% drier than average varies greatly locally. "It really goes from 0% to 100%", says Schellekens. "Last year it was 20% drier at the end of June, compared to the previous 15 years. This year we took a shorter period of 5 years. Another factor is the changing water quality as a result of the drought."
The satellite measures the soil moisture content to a depth of 5 centimeters. That doesn't seem like much, but according to the company, the top layer has a good predictive value for the groundwater level. The amount of moisture in the root zone is measured using calculation models. "Farmers are indirectly our customer," explains Robbert Mica, co-founder of VanderSat.
"Insurance companies worldwide use the data, but so do manufacturers of crop protection products. When using NDVI images, you suffer from clouds. That does not apply to this technology. We use passive microwaves. That sounds complicated, but the technology has been around for 40 years. Meteorologists use it to make weather models, filtering out the soil data, while we actually apply it," says Mica.
Niels van der Boom
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