Access to water is the biggest limiting factor for population growth. Without water, life (as we know it) cannot survive. Excessive heat and drought can limit population growth by lowering the availability of fresh, usable water to a population. Luckily, we humans are a very resourceful bunch, and have developed ways to manipulate our environment - so we are not in as much danger as animals. Nevertheless, this is an important reason to conserve water!

Weather conditions don't really limit the growth of a population. Climate does - the amount of water limits how dense plants can live in deserts, etc. Weather, however, only really affects populations through something called disturbance: storms, frosts, etc. kill off populations, but they don't limit them, because the population can recover from these types of events.

To think about weather conditions that limit population growth, let's look at how us humans have colonized the earth to see what trends we can find. If we imagine a hot day where it's hard to run and work, where we need to be drinking lots of water because we sweat to keep cool and avoid getting sick from heat stroke, we can imagine that it would be more difficult to survive in the heat than it would be somewhere with a moderate temperature. The same thing applies for very cold places, where we get frost bite and hypothermia if we stay outside in the cold. Let's look at some places on the earth that are very hot. In Australia some people have lived in the desert, but it's much more difficult to find food and water so most of Australia's population is in areas that are in cooler areas such as beside the ocean. In Canada, where it gets very cold in the winter, most of the population is located in the southern part of the country where it's slightly warmer instead of in the northern parts where it's the coldest (and thus hardest) place to live.

Just by looking at where humans have made cities, we can tell that heat and cold temperatures limit our populations. With today's modern technology it has become a little easier to survive in severe climate, by using air conditioning in the summer and heating our houses in the winter but it's much easier when you can be outside in the weather.