New yellow health heat alerts have come into force as the UK is set to be gripped by its fifth heatwave of the summer, with temperatures set to soar to 36C.The alerts run from 9am on Saturday to 9pm on Tuesday across all of England except the North East and North West and warn that the hot weather is likely to affect the wellbeing of the population, particularly those who are vulnerable or have health conditions.The warning comes after a string of record-breaking hot spells and the driest July on record, which have left half of England and the whole of Wales in drought and 26 million customers subject to a hosepipe ban.On Friday, the Environment Agency suggested several more areas could move towards or into drought next week after England received less than 10mm of rainfall for the seventh consecutive week.The Met Office said temperatures will climb through the weekend as heatwave conditions return, with a high of 36C expected in parts of East Anglia and south-east England by Thursday.The two record-breaking heatwaves of May and June led to more than 2,800 excess deaths, and two more heatwaves in July that have caused river levels to plummet and sparked wildfires.The highest temperature of the year was 38C recorded at Lingwood in Norfolk on June 28. There have been 33 days so far this year when temperatures have exceeded 30C somewhere in the UK. The record of 34 days – set in 1995 – is likely to be broken this week.UK temperatures are set to soar again this week in the fifth heatwave of the summerForecasters said the weekend will see a north-south split in the weather with Scotland and Northern Ireland likely to see spells of heavy rain, while England and Wales will remain largely dry, sunny and increasingly warm.Temperatures could reach 30C on Saturday, before climbing into the low 30s in southern and south-east England on Sunday.Highs of up to 30C are possible across parts of England and Wales on Tuesday, increasing to 32C to 34C on Wednesday, with the highest temperatures currently expected on Thursday.The UK Health Security Agency (UKHSA) has issued yellow heat health alerts for the East Midlands, West Midlands, South East, South West, East of England, Yorkshire and the Humber and London.Wildfires have left parts of the UK scorchedMeanwhile, the National Trust is asking people to sign a petition calling on the government to make tackling climate change a national mission.It comes after several wildfires have broken out in the UK over recent weeks, with large blazes at Dunwich Heath in Suffolk, Headon Warren on the Isle of Wight, Llanwonno in the Rhondda Valleys, South Wales, and the Cairngorms National Park in Scotland.Fires are likely to become exceptionally severe on Sunday for almost all of the east and south-east of England, according to the Fire Severity Index. “Exceptional” severity is its highest ranking.The Met Office data includes rainfall, temperature and humidity and agencies use the index to assess the severity of fire if it starts. It does not cover the chances of wildfires occurring.A cyclist in Richmond Park, London (Ben Whitley/PA)Reservoir storage in England has dropped to 69 per cent, down from 72 per cent a week ago and nearly 12 percentage points below the long-term average for the time of year, the Environment Agency said on Friday.Storage stood at 85 per cent at the end of June, which was the average for that point in the year, but has fallen steadily in recent weeks.Five reservoirs are now classed as having “exceptionally low” levels: Blagdon in Somerset (54 per cent full); Clywedog in Powys, which provides water for central and north-west England (62 per cent); the Dove group of reservoirs in Derbyshire (74 per cent); Hanningfield in Essex (60 per cent); and Wimbleball in Somerset (50 per cent).Last month was the driest July for England and Wales since records began in 1836, according to provisional figures released by the Met Office.Nineteen counties across England recorded effectively no rainfall – 1mm or less – across the whole of the month, Met Office figures show.