With an October heat wave and temperatures soaring into the high-30s and 40s, it is a timely reminder to make sure before you leave the carpark that everyone has at least 3 litres of water, and that you plan to finish the walk before midday.

Also, as leader, you should take the satellite phone and/or PLB with you in case of emergency.

Why we walk early and recommend to drink 3+ litres on summer bushwalks

In hot weather, we maintain a safe body temperature by evaporating sweat from bare skin. On really hot days, water loss from the body by sweating may reach 1.5 litres / hour.

The table below indicates the minimum water intake to maintain body fluid while at rest in the shade. There is generally little shade where we walk, and temperatures in the sun can be 10-15°C higher than that in the shade. Walking may double the stated water requirement.

Our normal (internal) body temperature is 37.2°C. A slight increase in body temperature is not unusual for people bushwalking under a hot sun. A body temperature of 38-39°C can be tolerated, but higher temperatures can lead to serious injury and death.

When the air temperature rises above skin temperature, heat loss can only be achieved by sweating.

Ongoing hydration: before, during & after the bushwalk

Begin hydration the night before the walk, and drink 0.5-1 litre of water in the morning before starting the walk. You will then be well hydrated at the start of the walk.

On the walk, it is better to drink small volumes regularly and often (250-350 mL every 20 minutes) to maintain fluid levels rather than drink a larger volume every hour.

Have additional cool water in the car to drink at the end of the walk, and keep drinking regularly for the rest of the day until your urine is clear.

Hyperthermia (heat illnesses)

Heat-related illnesses range from cramps to heat exhaustion and the life-threatening heat stroke.

Heat cramps are (often painful) muscle spasms caused by exercise and heavy sweating.

Treatment: Cramps can be relieved by rest in the shade, gentle massage, and taking oral fluids containing sodium (such as common salt, or gastrolyte).

Heat exhaustion is caused by a loss of salt and water from the body, usually by heavy sweating. Symptoms include headache, dizziness, nausea, chills and drowsiness. The skin may be warm or cool, with sweating. If left untreated, heat exhaustion can lead to heat stroke.

Treatment: The focus is on cooling and rehydration. The person should cease all activity and rest in the shade. Cool the skin by wetting and fanning. Give the person cool, lightly salted water (or electrolyte replacement). Fluid replacement of 1-2 litres over 2-4 hours is recommended. The person should rest over the next 24 hours, and not resume the activity until fully recovered.

If one person is suffering, then consider how others in the group are feeling as well.

If heat exhaustion is untreated, heat stroke may develop.

Heat stroke is a medical emergency with a mortality rate of 80% if not promptly and effectively treated. In this state, the body systems loses its ability to regulate body temperature (so sweating stops) resulting in an elevated core temperature. The organs literally ‘cook’ in our ‘body oven’. Signs and symptoms for heat exhaustion may be present, as well as a hot, red and dry skin, rapid pulse and breathing, and especially altered moods (irritability, confusion) and poor coordination.

Treatment: Immediate rapid cooling. Rest in shade, loosen and remove excess clothing, sprinkle with tepid water and fan aggressively, regularly towel dry skin, apply cold packs where blood vessels are close to the skin (neck, armpit, groin). Most patients with heat stroke are initially unconscious or semi-conscious and should not be given oral fluids.

Organise evacuation immediately.

Information sourced from Bushwalking and Ski Touring Leadership (2000) published by Bushwalking and Mountaincraft Training Advisory Board Inc.