Weather describes conditions now. Climate describes the long-term pattern and how much it varies.
Weather is the state of the atmosphere at a particular place and time. Its elements include air temperature, cloud cover, precipitation (such as rain), wind speed and wind direction. An afternoon thunderstorm is weather. Rainfall patterns over many years describe climate.
A standard climate normal is an average over 30 years, such as 1991-2020. Individual months can still be wetter or drier than this average. Before reading a climate graph, check its location, period and units.
Tropical equatorial climates stay warm all year, with a small annual temperature range and abundant rainfall. Tropical monsoon climates are also warm, but have more distinct wet and relatively dry seasons. Cool temperate climates are cooler, with a larger seasonal temperature change. Their rainfall patterns vary by location. Use the whole pattern to identify a climate type.
Climatic hazards can harm people and ecosystems. Heat waves bring prolonged heat, while drought reduces water supplies. Floods cover normally dry land and can damage homes, crops and habitats.
Tropical cyclones bring strong winds, heavy rain and sometimes a storm surge. Hot, dry weather favours wildfire where fuel and an ignition source are present. Whether a hazard becomes a disaster also depends on who or what is exposed and how vulnerable they are.
Step by step
Read the axes
Check the place, period and units. Rainfall and temperature use different axes.
Describe the year
State the main temperature and rainfall patterns, using months and values.
Calculate the range
Subtract the lowest monthly mean temperature from the highest.
Worked example: A precise graph description
Changi is warm throughout the year: monthly mean temperatures range from 26.8 to 28.6 degrees C. Rain falls in every month; December averages 331.9 mm compared with 105.1 mm in February. This describes the normal pattern, not the weather on a particular December day.
Watch out for this
A dry February means Singapore has a dry climate.
Relatively dry means drier than other months. Use the whole annual pattern and the stated long-term period before classifying climate.
Check your understanding
Which statement is evidence about climate?
- The wind changed direction at 2 pm today.
- Tomorrow afternoon may have thunderstorms.
- Monthly rainfall averaged over 1991-2020 is highest in December.