World weather review: April 2018

World weather review: April 2018

Mon, 14/05/2018 - 21:45
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The global surface temperatures of April 2018 were close to 0.5 °C above average compared to the reference period of 1981-2010. Although Europe was still experiencing cold, wet and windy conditions in early April, the month averaged out to be the warmest European April on record. The anomaly map below shows the temperature difference of April compared to the reference period of 1981-2010, with it notably warm over central parts of Europe.

Surface air temperature anomaly for April 2018 relative to the April average (1981-2010).  Red colours indicate higher, and blue colours lower than average temperature. Source: ERA-Interim. (Credit: ECMWF, Copernicus Climate Change Service)
Surface air temperature anomaly for April 2018 relative to the April average (1981-2010).  Red colours indicate higher, and blue colours lower than average temperature. Source: ERA-Interim. (Credit: ECMWF, Copernicus Climate Change Service)

 

During the Easter Bank Holiday Weekend (30th March - 2nd April), the UK experienced unsettled weather, including heavy rain and snow that resulted in an increase in river water levels in early April. The Environment Agency issued numerous flood warnings with the West Midlands, Northamptonshire, Cambridgeshire, Yorkshire and North Eastern England being amongst the most affected areas. The remainder of the month was warmer than average for most places in the UK.

Sea-ice cover for April 2018 is shown in the map below. Except for a stretch from north-eastern Greenland to Novaya Zemlya (Russia), where sea-ice cover was slightly above average, the Arctic Ocean and its adjacent land masses were warmer than normal. The average Arctic sea-ice extent for April 2018 was 13.7 million square kilometres, which was 980 000 square kilometres lower than the 1981-2010 average. This value is close to the low April record measured in 2016. Above average temperatures were also observed along the coasts of Antarctica and over the Ross and Weddell Seas, with sea-ice cover here below average.

Arctic sea-ice extent for April 2018 (white) in relation to the median ice edge of the reference period of 1981-2010 (National Snow and Ice Data Center, University of Colorado Boulder)
Arctic sea-ice extent for April 2018 (white) in relation to the median ice edge of the reference period of 1981-2010 (National Snow and Ice Data Center, University of Colorado Boulder)

 

Sydney, Australia, was threatened by severe bushfires in April 2018. Extreme heat together with strong winds in south-eastern Australia allowed the fires to spread quickly. April 2018 was the second warmest ever recorded April in Australia. In Nicaragua, Central America, the country also suffered from severe forest fires in the Indio Maíz biological reserve on Nicaragua’s Caribbean coast. The fire consumed over 50 km2 tropical rainforest – an area approximately as large as Oxford, England. Exceptionally hot temperatures were further recorded in eastern and central Pakistan, where the highest ever recorded April temperature of 50.2 °C was measured at the station Shaheed Benazirabad in south-eastern Pakistan.  

The severe droughts in Argentina that began in November 2017 continued into April 2018, where unusually high temperatures were present. As a result, the corn and soybean harvest are expected to be the poorest in at least a decade. NASA’s “Soil Moisture Active Passive” (SMAP) satellite is able to capture the drought, as it can detect the severe reduction in soil moisture that goes hand in hand with drought. The effect of the drought is visible between both images. 

The above image compares soil moisture content of the fertile Pampas region of central Argentina between April 2017 (left) and April 2018 (right). Dark green and blue colours indicate a high soil moisture content. Credit: NASA Earth Observatory images by Joshua Stevens (Data: JPL, SMAP Science Team)
The above image compares soil moisture content of the fertile Pampas region of central Argentina between April 2017 (left) and April 2018 (right). Dark green and blue colours indicate a high soil moisture content. Credit: NASA Earth Observatory images by Joshua Stevens (Data: JPL, SMAP Science Team)

 

Mexico, the Southwest of the US, North Africa, China and Mongolia also experienced markedly above-average temperatures, by approximately. In contrast, the central US and large parts of Canada experienced a colder than average April with frequent snowstorms and blizzards. Over the oceans, colder than normal conditions dominated the eastern tropical Pacific and large parts of the tropical Atlantic.

Above average rainfall and flooding occurred in the East and Horn of Africa. Hundreds of thousands of people in Ethiopia, Kenya, Somalia, Tanzania and Uganda are affected by severe flash and river flooding. The heaviest 24-hour rainfall ever recorded in the USA occurred between April 14 and 15 at a rain gauge in Kauai, Hawaii. 1 262 mm of rain were reported at that site.