Heat waves

What a heat dome is

A heat dome is an area of extremely high pressure that settles over a region for several days, pressing hot air downwards and stopping it from circulating. The effect is like a closed oven: temperatures rise day after day, and night brings no relief because the hot air does not escape.

Portugal has been recording heat domes increasingly early, with temperatures close to 40°C already in May in some events over the last decade — several weeks before the traditional July/August peak. These episodes have shifted from "rare" to recurring.

Why it is more dangerous than a normal heatwave

• No night-time relief: the body does not recover overnight (minimums above 25°C)
• Lasts 5-14 days: mortality climbs sharply after the 3rd consecutive day
• Portuguese homes cope badly with heat (built for the cold, not the heat — without proper insulation)
• Electrical overload: blackouts from excessive AC use
• Wildfires in parallel: dry air and wind
• Drought makes it worse: low rivers and wells, livestock affected

Very high risk

• Elderly (over 65): reduced thermoregulation, diminished sense of thirst
• Babies and young children (under 5): dehydrate rapidly
• Chronic illness: cardiovascular, renal, diabetes, respiratory conditions
• Bedridden individuals: unable to seek cooler environments

High risk

• Outdoor workers: construction, agriculture, waste collection
• People exercising outdoors
• Obese individuals: greater difficulty dissipating heat
• Homeless people: no access to shelter or water

Check on your neighbours

• Visit elderly people living alone at least twice a day
• Make sure they drink water regularly
• Take them to cool spaces if they do not have air conditioning
• Check their medication, it may need adjusting (see guide)

Heat exhaustion

Severity: Moderate, needs attention

• Heavy sweating
• Cool, clammy skin
• Weakness, dizziness, nausea
• Headache
• Muscle cramps
• Rapid but weak pulse

Heat stroke

Severity: MEDICAL EMERGENCY, can be fatal

• Body temperature above 40°C
• Hot, red, and DRY skin (no sweating)
• Confusion, delirium
• Loss of consciousness
• Seizures
• Rapid and strong pulse

Hydration

• Drink 2-3 litres of water per day even if you are not thirsty
• Avoid alcohol, coffee, and sugary drinks (they dehydrate)
• Eat water-rich fruit: watermelon, melon, oranges, cucumber
• Cold soups (gazpacho) and salads
• Avoid heavy, hot meals
• Children and elderly: offer water every 20-30 minutes

Behaviour

• Avoid sun exposure between 11:00 and 17:00
• Lightweight, light-coloured, loose clothing (cotton or linen)
• Wide-brimmed hat and sunglasses
• Sunscreen SPF 50+ (reapply every 2 hours)
• Cool baths or showers (not ice-cold)
• Exercise: only early morning or late evening
• NEVER leave children or animals in a car

Protecting your home

• Close shutters and blinds on the sunny side
• Ventilate at night and early morning (open windows)
• Close windows in the morning as the temperature rises
• Hang damp cloths in front of fans
• If you do not have AC: spend the hottest hours in an air-conditioned public space (shopping centre, library)
• Plants outside south-facing windows provide natural shade

Pets

• Fresh water always available and in the shade
• NEVER walk dogs on hot tarmac (test: if you cannot hold your hand on the ground for 5 seconds, it is too hot for their paws)
• Walks only early morning or in the evening
• Signs of heat stroke in dogs: excessive panting, thick drool, disorientation
• Cats: ensure access to cool rooms
• See the full guide for pets

Insulin — essential rules

• Unopened (sealed vial/pen): 2-8°C (fridge), until the expiry date
• In use (opened pen): can stay at room temperature up to 25-30°C for 28 days (check the leaflet — variants such as Lantus and some analogues have their own rules)
• Above 30°C or in direct sunlight: loses effectiveness, discard
• NEVER freeze: the molecule's structure is destroyed — useless even if thawed
• NEVER leave in the car (interior temperatures reach 60-70°C in summer)
• When travelling, use a medication cool pouch

Other refrigerated medications

• GLP-1 (Ozempic, Saxenda, Trulicity): ideal at 2-8°C; once opened, withstands up to 30°C for 28-56 days (check the leaflet)
• Vaccines (kept at home, e.g. for campaigns): always 2-8°C — use a fridge thermometer
• Adrenaline (EpiPen, Anapen): 15-25°C — do not refrigerate (cold also degrades it). Cloudy or yellowish liquid = discard
• Eye drops once opened: some need refrigeration (check the leaflet)
• Antibiotics in suspension (paediatric, once reconstituted): usually 2-8°C, 7-14 days
• Thyroid hormones and oral contraceptives: below 30°C is enough, no fridge needed

Without a fridge (blackout or breakdown)

• Closed fridge: stays safe for about 4 hours
• Cool pouch + ice packs (supermarket cool bag): holds 4-8°C for 12-24 hours
• Do not place insulin in direct contact with ice (risk of freezing): wrap it in cloth or a tea towel
• Frozen 1.5-litre bottles work as homemade ice packs
• Large camping cool box + 2-3 eutectic plates: 24-48 hours at 4-10°C
• Neighbour/friend with a generator or power: move refrigerated medication there

Cooling without electricity — the zeer pot method

An ancient evaporative cooling technique that needs no power. Keeps things 5-10°C below the ambient temperature:

• 2 clay pots: 1 larger, 1 smaller that fits inside with 3-5 cm clearance
• Fill that gap with damp sand
• Cover the inner pot with a damp cloth
• Keep in the shade, in a breeze, off the ground
• Wet the sand 1-2 times a day
• Useful for food, vegetables, eggs and non-refrigerated medication
• Does not replace a fridge for insulin — only a partial alternative

Emergency

• 112, Emergency
• E-REDES (power outages): 800 506 506
• SNS 24 (health line): 808 24 24 24

Alerts

• IPMA (weather and geophysics institute): ipma.pt
• IPMA alerts guide
• IPMA app (temperature alerts)

Support

• Linha do Idoso (elderly helpline): 800 203 531
• ANEPC (Civil Protection): 800 246 246
• All contacts